- 新增 .drone.yml 文件用于定义 CI/CD 流程 - 配置了基于 Docker 的部署步骤 - 设置了工作区和卷映射以支持持久化数据 - 添加了构建准备阶段和 Docker 部署阶段 - 定义了环境变量和代理设置 - 配置了 artifacts 目录的处理逻辑 - 添加了 timezone 映射以确保时间同步 - 设置了 docker.sock 映射以支持 Docker in Docker
1 line
363 KiB
JavaScript
1 line
363 KiB
JavaScript
(window.webpackJsonp=window.webpackJsonp||[]).push([[20],{502:function(s,a,t){"use strict";t.r(a);var n=t(2),e=Object(n.a)({},(function(){var s=this,a=s._self._c;return a("ContentSlotsDistributor",{attrs:{"slot-key":s.$parent.slotKey}},[a("h2",{attrs:{id:"_1-类文件结构"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-类文件结构"}},[s._v("#")]),s._v(" 1 类文件结构")]),s._v(" "),a("p",[s._v("一个简单的 HelloWorld.java 文件")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("HelloWorld")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"Hello World"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br")])]),a("p",[s._v("将其执行 "),a("code",[s._v("javac -parameters -d . HelloWorld.java")]),s._v(" 编译后的 HelloWorld.class 文件如下(Notepad++使用十六进制进行查看)")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670046032461.png",alt:"1670046032461"}})]),s._v(" "),a("p",[s._v("根据 JVM 规范,类文件结构如下,这是在 JVM 运行中的所有字节码文件都需要遵循的")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("class-file {\n u4 magic;\t//魔数\n u2 minor_version;\t//小版本号\n u2 major_version;\t//大版本号\n u2 constant_pool_count;\t//常量池中常量个数+1\n cp_info constant_pool[constant_pool_count-1];\t//常量池\n u2 access_flags;\t//类的访问控制符标识(public,static,final,abstract等)\n u2 this_class;\t//该类的描述(值为对常量池的引用,引用的值为CONSTANT_Class_info)\n u2 super_class;\t//父类的描述(值为对常量池的引用,引用的值为CONSTANT_Class_info)\n u2 interfaces_count;\t//接口数量\n u2 interfaces[interfaces_count];\t//接口的描述(每个都是对常量池的引用)\n u2 fields_count;\t//变量数,包括该类中或接口中类变量和实例变量\n field_info fields[fields_count];\t//变量表集合\n u2 methods_count;\t//方法数,包括该类中或接口中定义的所有方法\n method_info methods[methods_count];\t//方法表集合\n u2 attributes_count;\t//属性数,包括InnerClasses,EnclosingMethod,SourceFile等\n attribute_info attributes[attributes_count];\t//属性表集合\n}\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br")])]),a("h3",{attrs:{id:"_1-1-魔数"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-1-魔数"}},[s._v("#")]),s._v(" 1.1 魔数")]),s._v(" "),a("p",[s._v("0-3 字节,表示它是否是【class】类型的文件")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670046677428.png",alt:"1670046677428"}})]),s._v(" "),a("h3",{attrs:{id:"_1-2-版本"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-2-版本"}},[s._v("#")]),s._v(" 1.2 版本")]),s._v(" "),a("p",[s._v("4-7 字节,表示类的版本 00 34(52) 表示是 Java 8")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670046787159.png",alt:"1670046787159"}})]),s._v(" "),a("h3",{attrs:{id:"_1-3-常量池"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-3-常量池"}},[s._v("#")]),s._v(" 1.3 常量池")]),s._v(" "),a("p",[s._v("8-9 字节,表示常量池长度,00 1f (31) 表示常量池有 #1- #30 项,注意 #0 项不计入,也没有值,可以发现一个 Class 文件中最多具备 65535(2^16) 个常量,它包括了以下所有类型。")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670047109146.png",alt:"1670047109146"}})]),s._v(" "),a("p",[s._v("常量池类型映射表,目前为止 JVM 一共定义了 14 种类型的常量。")]),s._v(" "),a("table",[a("thead",[a("tr",[a("th",[s._v("Constant Type")]),s._v(" "),a("th",[s._v("Value")]),s._v(" "),a("th",[s._v("Length(Byte)")]),s._v(" "),a("th",[s._v("Tip")])])]),s._v(" "),a("tbody",[a("tr",[a("td",[s._v("CONSTANT_Class")]),s._v(" "),a("td",[s._v("7")]),s._v(" "),a("td",[s._v("2")]),s._v(" "),a("td",[s._v("Class信息")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_Fieldref")]),s._v(" "),a("td",[s._v("9")]),s._v(" "),a("td",[s._v("4")]),s._v(" "),a("td",[s._v("成员变量信息,前2为 CONSTANT_Class,后2为 CONSTANT_NameAndType")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_Methodref")]),s._v(" "),a("td",[s._v("10")]),s._v(" "),a("td",[s._v("4")]),s._v(" "),a("td",[s._v("方法信息,前2为 CONSTANT_Class,后2为 CONSTANT_NameAndType")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_InterfaceMethodref")]),s._v(" "),a("td",[s._v("11")]),s._v(" "),a("td",[s._v("4")]),s._v(" "),a("td",[s._v("接口方法信息,前2为 CONSTANT_Class,后2为 CONSTANT_NameAndType")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_String")]),s._v(" "),a("td",[s._v("8")]),s._v(" "),a("td",[s._v("2")]),s._v(" "),a("td",[s._v("字符串常量名称")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_Integer")]),s._v(" "),a("td",[s._v("3")]),s._v(" "),a("td",[s._v("4")]),s._v(" "),a("td",[s._v("int值")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_Float")]),s._v(" "),a("td",[s._v("4")]),s._v(" "),a("td",[s._v("4")]),s._v(" "),a("td",[s._v("float值")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_Long")]),s._v(" "),a("td",[s._v("5")]),s._v(" "),a("td",[s._v("8")]),s._v(" "),a("td",[s._v("long值")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_Double")]),s._v(" "),a("td",[s._v("6")]),s._v(" "),a("td",[s._v("8")]),s._v(" "),a("td",[s._v("double值")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_NameAndType")]),s._v(" "),a("td",[s._v("12")]),s._v(" "),a("td",[s._v("4")]),s._v(" "),a("td",[s._v("名称和类型信息,前2为 命名信息,后2为 类型信息")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_Utf8")]),s._v(" "),a("td",[s._v("1")]),s._v(" "),a("td",[s._v("2")]),s._v(" "),a("td",[s._v("长度记录了该字符串的长度,通过该记录的长度来读取后续相应字节长度信息")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_MethodHandle")]),s._v(" "),a("td",[s._v("15")]),s._v(" "),a("td",[s._v("-")]),s._v(" "),a("td",[s._v("表示方法句柄(后续遇到再补充)")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_MethodType")]),s._v(" "),a("td",[s._v("16")]),s._v(" "),a("td",[s._v("-")]),s._v(" "),a("td",[s._v("表示方法类型(后续遇到再补充)")])]),s._v(" "),a("tr",[a("td",[s._v("CONSTANT_InvokeDynamic")]),s._v(" "),a("td",[s._v("18")]),s._v(" "),a("td",[s._v("-")]),s._v(" "),a("td",[s._v("表示一个动态方法调用点(后续遇到再补充)")])])])]),s._v(" "),a("p",[s._v("根据以上映射表来对其余字节码的分析")]),s._v(" "),a("p",[s._v("常量池中 #1 项 0a(10),由映射表得知是一个 Method 信息,其通过后续的 00 06(6) 和 00 11(17) 分别表示该方法的【所属类】引用常量池中 #6 项、【方法名】引用常量池中 #17 项。")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670048081295.png",alt:"1670048081295"}})]),s._v(" "),a("p",[s._v("常量池中 #2 项 09(9),由映射表得知是一个 Field 信息,其通过后续的 00 12(18) 和 00 13(19) 分别表示该成员变量的【所属类】引用常量池中 #18 项、【成员变量名】引用常量池中 #19 项。")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670048493839.png",alt:"1670048493839"}})]),s._v(" "),a("p",[s._v("常量池中 #3 项 08(8),由映射表得知是一个字符串常量名称,其通过后续的 00 14(20)表示其引用了常量池中 #20 项。")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670048714141.png",alt:"1670048714141"}})]),s._v(" "),a("p",[s._v("依此类推进行其他常量池的解析,这里就不演示了,了解一个解析形式即可。")]),s._v(" "),a("p",[s._v("以上分析结果的常量池大概就是使用反编译后的常量池结果,而且可以看到所有的字符串常量池中的信息一一对应")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v('#1 = Methodref #6.#17 // java/lang/Object."<init>":()V\n#2 = Fieldref #18.#19 // java/lang/System.out:Ljava/io/PrintStream;\n#3 = String #20 // Hello World\n#4 = Methodref #21.#22 // java/io/PrintStream.println:(Ljava/lang/String;)V\n#5 = Class #23 // HelloWorld\n#6 = Class #24 // java/lang/Object\n#7 = Utf8 <init>\n#8 = Utf8 ()V\n#9 = Utf8 Code\n#10 = Utf8 LineNumberTable\n#11 = Utf8 main\n#12 = Utf8 ([Ljava/lang/String;)V\n#13 = Utf8 MethodParameters\n#14 = Utf8 args\n#15 = Utf8 SourceFile\n#16 = Utf8 HelloWorld.java\n#17 = NameAndType #7:#8 // "<init>":()V\n#18 = Class #25 // java/lang/System\n#19 = NameAndType #26:#27 // out:Ljava/io/PrintStream;\n#20 = Utf8 Hello World\n#21 = Class #28 // java/io/PrintStream\n#22 = NameAndType #29:#30 // println:(Ljava/lang/String;)V\n#23 = Utf8 HelloWorld\n#24 = Utf8 java/lang/Object\n#25 = Utf8 java/lang/System\n#26 = Utf8 out\n#27 = Utf8 Ljava/io/PrintStream;\n#28 = Utf8 java/io/PrintStream\n#29 = Utf8 println\n#30 = Utf8 (Ljava/lang/String;)V\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br"),a("span",{staticClass:"line-number"},[s._v("28")]),a("br"),a("span",{staticClass:"line-number"},[s._v("29")]),a("br"),a("span",{staticClass:"line-number"},[s._v("30")]),a("br")])]),a("h3",{attrs:{id:"_1-4-访问标识与继承信息"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-4-访问标识与继承信息"}},[s._v("#")]),s._v(" 1.4 访问标识与继承信息")]),s._v(" "),a("p",[s._v("解析完常量池后的8的字节,就是该部分的信息")]),s._v(" "),a("ul",[a("li",[s._v("2:该class类型和访问修饰符Flag")]),s._v(" "),a("li",[s._v("2:通过常量池找到本类全限定名")]),s._v(" "),a("li",[s._v("2:通过常量池找到父类全限定名")]),s._v(" "),a("li",[s._v("2:表示接口数量")])]),s._v(" "),a("table",[a("thead",[a("tr",[a("th",[s._v("Flag Name")]),s._v(" "),a("th",[s._v("Value")]),s._v(" "),a("th",[s._v("Interpretation")])])]),s._v(" "),a("tbody",[a("tr",[a("td",[s._v("ACC_PUBLIC")]),s._v(" "),a("td",[s._v("0x0001")]),s._v(" "),a("td",[s._v("public 访问权限")])]),s._v(" "),a("tr",[a("td",[s._v("ACC_FINAL")]),s._v(" "),a("td",[s._v("0x0010")]),s._v(" "),a("td",[s._v("final 修饰符")])]),s._v(" "),a("tr",[a("td",[s._v("ACC_SUPER")]),s._v(" "),a("td",[s._v("0x0020")]),s._v(" "),a("td",[s._v("Treat "),a("code",[s._v("superclass")]),s._v(" methods specially when invoked by the invokespecial instruction. 父类调用方式")])]),s._v(" "),a("tr",[a("td",[s._v("ACC_INTERFACE")]),s._v(" "),a("td",[s._v("0x0200")]),s._v(" "),a("td",[s._v("interface 类型")])]),s._v(" "),a("tr",[a("td",[s._v("ACC_ABSTRACT")]),s._v(" "),a("td",[s._v("0x0400")]),s._v(" "),a("td",[s._v("abstract 类型")])]),s._v(" "),a("tr",[a("td",[s._v("ACC_SYNTHETIC")]),s._v(" "),a("td",[s._v("0x1000")]),s._v(" "),a("td",[s._v("通过合成/生成的代码,没有源代码")])]),s._v(" "),a("tr",[a("td",[s._v("ACC_ANNOTATION")]),s._v(" "),a("td",[s._v("0x2000")]),s._v(" "),a("td",[s._v("annotation 类型")])]),s._v(" "),a("tr",[a("td",[s._v("ACC_ENUM")]),s._v(" "),a("td",[s._v("0x4000")]),s._v(" "),a("td",[s._v("enum 类型")])])])]),s._v(" "),a("h3",{attrs:{id:"_1-5-field-信息"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-5-field-信息"}},[s._v("#")]),s._v(" 1.5 Field 信息")]),s._v(" "),a("p",[s._v("解析完以上的信息的后续2字节,表示成员变量的数量,此案例文件并没有成员变量")]),s._v(" "),a("table",[a("thead",[a("tr",[a("th",[s._v("FieldType")]),s._v(" "),a("th",[s._v("Type")]),s._v(" "),a("th",[s._v("Interpretation")])])]),s._v(" "),a("tbody",[a("tr",[a("td",[s._v("B")]),s._v(" "),a("td",[s._v("byte")]),s._v(" "),a("td")]),s._v(" "),a("tr",[a("td",[s._v("C")]),s._v(" "),a("td",[s._v("char")]),s._v(" "),a("td")]),s._v(" "),a("tr",[a("td",[s._v("D")]),s._v(" "),a("td",[s._v("double")]),s._v(" "),a("td")]),s._v(" "),a("tr",[a("td",[s._v("F")]),s._v(" "),a("td",[s._v("float")]),s._v(" "),a("td")]),s._v(" "),a("tr",[a("td",[s._v("I")]),s._v(" "),a("td",[s._v("int")]),s._v(" "),a("td")]),s._v(" "),a("tr",[a("td",[s._v("J")]),s._v(" "),a("td",[s._v("long")]),s._v(" "),a("td")]),s._v(" "),a("tr",[a("td",[s._v("L"),a("code",[s._v("ClassName")]),s._v(";")]),s._v(" "),a("td",[s._v("reference")]),s._v(" "),a("td",[s._v("引用类型")])]),s._v(" "),a("tr",[a("td",[s._v("S")]),s._v(" "),a("td",[s._v("short")]),s._v(" "),a("td")]),s._v(" "),a("tr",[a("td",[s._v("Z")]),s._v(" "),a("td",[s._v("boolean")]),s._v(" "),a("td")]),s._v(" "),a("tr",[a("td",[s._v("[")]),s._v(" "),a("td",[s._v("reference")]),s._v(" "),a("td",[s._v("一维数组")])])])]),s._v(" "),a("h3",{attrs:{id:"_1-6-method-信息"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-6-method-信息"}},[s._v("#")]),s._v(" 1.6 Method 信息")]),s._v(" "),a("p",[s._v("解析完以上的信息的后续2字节,表示方法的数量")]),s._v(" "),a("p",[s._v("一个方法由 访问修饰符,名称,参数描述,方法属性数量,方法属性组成")]),s._v(" "),a("p",[s._v("就是解析为以下反编译文件(使用十六进制分析过程过于庞大)")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v('{\n public HelloWorld();\n descriptor: ()V\n flags: ACC_PUBLIC\n Code:\n stack=1, locals=1, args_size=1\n 0: aload_0\n 1: invokespecial #1 // Method java/lang/Object."<init>":()V\n 4: return\n LineNumberTable:\n line 1: 0\n\n public static void main(java.lang.String[]);\n descriptor: ([Ljava/lang/String;)V\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=2, locals=1, args_size=1\n 0: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;\n 3: ldc #3 // String Hello World\n 5: invokevirtual #4 // Method java/io/PrintStream.println:(Ljava/lang/String;)V\n 8: return\n LineNumberTable:\n line 3: 0\n line 4: 8\n MethodParameters:\n Name Flags\n args\n}\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br"),a("span",{staticClass:"line-number"},[s._v("28")]),a("br")])]),a("h3",{attrs:{id:"_1-7-附加属性"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-7-附加属性"}},[s._v("#")]),s._v(" 1.7 附加属性")]),s._v(" "),a("p",[s._v("解析为以下反编译文件的内容")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v('SourceFile: "HelloWorld.java"\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br")])]),a("p",[s._v("参考文献 https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html")]),s._v(" "),a("h2",{attrs:{id:"_2-字节码指令"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-字节码指令"}},[s._v("#")]),s._v(" 2 字节码指令")]),s._v(" "),a("h3",{attrs:{id:"_2-1-入门"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-1-入门"}},[s._v("#")]),s._v(" 2.1 入门")]),s._v(" "),a("p",[s._v("分析方法中的字节码指令信息")]),s._v(" "),a("p",[s._v("构造方法对应的字节码信息如下图,对应的反编译信息如下文本块所示")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670054933674.png",alt:"1670054933674"}})]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v(' public HelloWorld();\n descriptor: ()V\n flags: ACC_PUBLIC\n Code:\n stack=1, locals=1, args_size=1\n 0: aload_0\n 1: invokespecial #1 // Method java/lang/Object."<init>":()V\n 4: return\n LineNumberTable:\n line 1: 0\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br")])]),a("p",[s._v("有以下对应关系")]),s._v(" "),a("ul",[a("li",[s._v("2a => aload_0:加载 slot 0 的局部变量,即 this,做为下面的 invokespecial 构造方法调用的参数")]),s._v(" "),a("li",[s._v("b7 => invokespecial:预备调用构造方法,哪个方法呢?")]),s._v(" "),a("li",[s._v('00 01:引用常量池中 #1 项,即【 Method java/lang/Object.""😦)V 】')]),s._v(" "),a("li",[s._v("b1:表示返回")])]),s._v(" "),a("p",[s._v("main方法对应的字节码信息如下图,对应的反编译信息如下文本块所示")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670055197971.png",alt:"1670055197971"}})]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v(" public static void main(java.lang.String[]);\n descriptor: ([Ljava/lang/String;)V\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=2, locals=1, args_size=1\n 0: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;\n 3: ldc #3 // String Hello World\n 5: invokevirtual #4 // Method java/io/PrintStream.println:(Ljava/lang/String;)V\n 8: return\n LineNumberTable:\n line 3: 0\n line 4: 8\n MethodParameters:\n Name Flags\n args\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br")])]),a("p",[s._v("有以下对应关系")]),s._v(" "),a("ul",[a("li",[s._v("b2 => getstatic:用来加载静态变量,哪个静态变量呢?")]),s._v(" "),a("li",[s._v("00 02:引用常量池中 #2 项,即【Field java/lang/System.out:Ljava/io/PrintStream;】")]),s._v(" "),a("li",[s._v("12 => ldc:加载参数,哪个参数呢?")]),s._v(" "),a("li",[s._v("03:引用常量池中 #3 项,即 【String Hello World】")]),s._v(" "),a("li",[s._v("b6 => invokevirtual:预备调用成员方法,哪个方法呢?")]),s._v(" "),a("li",[s._v("00 04:引用常量池中 #4 项,即【Method java/io/PrintStream.println:(Ljava/lang/String;)V】")]),s._v(" "),a("li",[s._v("b1:表示返回")])]),s._v(" "),a("p",[s._v("请参考 "),a("a",{attrs:{href:"https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-6.html#jvms-6.5",target:"_blank",rel:"noopener noreferrer"}},[s._v("https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-6.html#jvms-6.5"),a("OutboundLink")],1)]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670055453251.png",alt:"1670055453251"}})]),s._v(" "),a("h3",{attrs:{id:"_2-2-javap-工具"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-2-javap-工具"}},[s._v("#")]),s._v(" 2.2 javap 工具")]),s._v(" "),a("p",[s._v("自己分析类文件结构太麻烦了,Oracle 提供了 javap 工具来反编译 class 文件")]),s._v(" "),a("p",[s._v("使用命令 "),a("code",[s._v("javap -v HelloWorld.class")]),s._v(",查看完整的反编译信息")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v('Classfile /G:/Idea_workspace/JVM/src/main/java/HelloWorld.class\n Last modified 2022-12-3; size 462 bytes\n MD5 checksum f882f9f216fff39f1b95dd6b16b209a7\n Compiled from "HelloWorld.java"\npublic class HelloWorld\n minor version: 0\n major version: 52\n flags: ACC_PUBLIC, ACC_SUPER\nConstant pool:\n #1 = Methodref #6.#17 // java/lang/Object."<init>":()V\n #2 = Fieldref #18.#19 // java/lang/System.out:Ljava/io/PrintStream;\n #3 = String #20 // Hello World\n #4 = Methodref #21.#22 // java/io/PrintStream.println:(Ljava/lang/String;)V\n #5 = Class #23 // HelloWorld\n #6 = Class #24 // java/lang/Object\n #7 = Utf8 <init>\n #8 = Utf8 ()V\n #9 = Utf8 Code\n #10 = Utf8 LineNumberTable\n #11 = Utf8 main\n #12 = Utf8 ([Ljava/lang/String;)V\n #13 = Utf8 MethodParameters\n #14 = Utf8 args\n #15 = Utf8 SourceFile\n #16 = Utf8 HelloWorld.java\n #17 = NameAndType #7:#8 // "<init>":()V\n #18 = Class #25 // java/lang/System\n #19 = NameAndType #26:#27 // out:Ljava/io/PrintStream;\n #20 = Utf8 Hello World\n #21 = Class #28 // java/io/PrintStream\n #22 = NameAndType #29:#30 // println:(Ljava/lang/String;)V\n #23 = Utf8 HelloWorld\n #24 = Utf8 java/lang/Object\n #25 = Utf8 java/lang/System\n #26 = Utf8 out\n #27 = Utf8 Ljava/io/PrintStream;\n #28 = Utf8 java/io/PrintStream\n #29 = Utf8 println\n #30 = Utf8 (Ljava/lang/String;)V\n{\n public HelloWorld();\n descriptor: ()V\n flags: ACC_PUBLIC\n Code:\n stack=1, locals=1, args_size=1\n 0: aload_0\n 1: invokespecial #1 // Method java/lang/Object."<init>":()V\n 4: return\n LineNumberTable:\n line 1: 0\n\n public static void main(java.lang.String[]);\n descriptor: ([Ljava/lang/String;)V\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=2, locals=1, args_size=1\n 0: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;\n 3: ldc #3 // String Hello World\n 5: invokevirtual #4 // Method java/io/PrintStream.println:(Ljava/lang/String;)V\n 8: return\n LineNumberTable:\n line 3: 0\n line 4: 8\n MethodParameters:\n Name Flags\n args\n}\nSourceFile: "HelloWorld.java"\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br"),a("span",{staticClass:"line-number"},[s._v("28")]),a("br"),a("span",{staticClass:"line-number"},[s._v("29")]),a("br"),a("span",{staticClass:"line-number"},[s._v("30")]),a("br"),a("span",{staticClass:"line-number"},[s._v("31")]),a("br"),a("span",{staticClass:"line-number"},[s._v("32")]),a("br"),a("span",{staticClass:"line-number"},[s._v("33")]),a("br"),a("span",{staticClass:"line-number"},[s._v("34")]),a("br"),a("span",{staticClass:"line-number"},[s._v("35")]),a("br"),a("span",{staticClass:"line-number"},[s._v("36")]),a("br"),a("span",{staticClass:"line-number"},[s._v("37")]),a("br"),a("span",{staticClass:"line-number"},[s._v("38")]),a("br"),a("span",{staticClass:"line-number"},[s._v("39")]),a("br"),a("span",{staticClass:"line-number"},[s._v("40")]),a("br"),a("span",{staticClass:"line-number"},[s._v("41")]),a("br"),a("span",{staticClass:"line-number"},[s._v("42")]),a("br"),a("span",{staticClass:"line-number"},[s._v("43")]),a("br"),a("span",{staticClass:"line-number"},[s._v("44")]),a("br"),a("span",{staticClass:"line-number"},[s._v("45")]),a("br"),a("span",{staticClass:"line-number"},[s._v("46")]),a("br"),a("span",{staticClass:"line-number"},[s._v("47")]),a("br"),a("span",{staticClass:"line-number"},[s._v("48")]),a("br"),a("span",{staticClass:"line-number"},[s._v("49")]),a("br"),a("span",{staticClass:"line-number"},[s._v("50")]),a("br"),a("span",{staticClass:"line-number"},[s._v("51")]),a("br"),a("span",{staticClass:"line-number"},[s._v("52")]),a("br"),a("span",{staticClass:"line-number"},[s._v("53")]),a("br"),a("span",{staticClass:"line-number"},[s._v("54")]),a("br"),a("span",{staticClass:"line-number"},[s._v("55")]),a("br"),a("span",{staticClass:"line-number"},[s._v("56")]),a("br"),a("span",{staticClass:"line-number"},[s._v("57")]),a("br"),a("span",{staticClass:"line-number"},[s._v("58")]),a("br"),a("span",{staticClass:"line-number"},[s._v("59")]),a("br"),a("span",{staticClass:"line-number"},[s._v("60")]),a("br"),a("span",{staticClass:"line-number"},[s._v("61")]),a("br"),a("span",{staticClass:"line-number"},[s._v("62")]),a("br"),a("span",{staticClass:"line-number"},[s._v("63")]),a("br"),a("span",{staticClass:"line-number"},[s._v("64")]),a("br"),a("span",{staticClass:"line-number"},[s._v("65")]),a("br"),a("span",{staticClass:"line-number"},[s._v("66")]),a("br"),a("span",{staticClass:"line-number"},[s._v("67")]),a("br"),a("span",{staticClass:"line-number"},[s._v("68")]),a("br")])]),a("h3",{attrs:{id:"_2-3-图解方法执行流程"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-3-图解方法执行流程"}},[s._v("#")]),s._v(" 2.3 图解方法执行流程")]),s._v(" "),a("h4",{attrs:{id:"_1-原始-java-代码"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-原始-java-代码"}},[s._v("#")]),s._v(" 1) 原始 Java 代码")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("package")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token namespace"}},[s._v("com"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("zhuhjay"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("demo3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" b "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Short")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("MAX_VALUE")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" c "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br")])]),a("h4",{attrs:{id:"_2-编译后的字节码文件"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-编译后的字节码文件"}},[s._v("#")]),s._v(" 2) 编译后的字节码文件")]),s._v(" "),a("p",[s._v("使用命令 "),a("code",[s._v("javap -v Demo3_1.class")]),s._v(" 进行反编译,查看字节码")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v('Classfile /G:/Idea_workspace/JVM/target/classes/com/zhuhjay/demo3/Demo3_1.class\n Last modified 2022-12-3; size 619 bytes\n MD5 checksum 2f036be3ec6ee9204c53f83b17dacc1f\n Compiled from "Demo3_1.java"\npublic class com.zhuhjay.demo3.Demo3_1\n minor version: 0\n major version: 52\n flags: ACC_PUBLIC, ACC_SUPER\nConstant pool:\n #1 = Methodref #7.#25 // java/lang/Object."<init>":()V\n #2 = Class #26 // java/lang/Short\n #3 = Integer 32768\n #4 = Fieldref #27.#28 // java/lang/System.out:Ljava/io/PrintStream;\n #5 = Methodref #29.#30 // java/io/PrintStream.println:(I)V\n #6 = Class #31 // com/zhuhjay/demo3/Demo3_1\n #7 = Class #32 // java/lang/Object\n #8 = Utf8 <init>\n #9 = Utf8 ()V\n #10 = Utf8 Code\n #11 = Utf8 LineNumberTable\n #12 = Utf8 LocalVariableTable\n #13 = Utf8 this\n #14 = Utf8 Lcom/zhuhjay/demo3/Demo3_1;\n #15 = Utf8 main\n #16 = Utf8 ([Ljava/lang/String;)V\n #17 = Utf8 args\n #18 = Utf8 [Ljava/lang/String;\n #19 = Utf8 a\n #20 = Utf8 I\n #21 = Utf8 b\n #22 = Utf8 c\n #23 = Utf8 SourceFile\n #24 = Utf8 Demo3_1.java\n #25 = NameAndType #8:#9 // "<init>":()V\n #26 = Utf8 java/lang/Short\n #27 = Class #33 // java/lang/System\n #28 = NameAndType #34:#35 // out:Ljava/io/PrintStream;\n #29 = Class #36 // java/io/PrintStream\n #30 = NameAndType #37:#38 // println:(I)V\n #31 = Utf8 com/zhuhjay/demo3/Demo3_1\n #32 = Utf8 java/lang/Object\n #33 = Utf8 java/lang/System\n #34 = Utf8 out\n #35 = Utf8 Ljava/io/PrintStream;\n #36 = Utf8 java/io/PrintStream\n #37 = Utf8 println\n #38 = Utf8 (I)V\n{\n public com.zhuhjay.demo3.Demo3_1();\n descriptor: ()V\n flags: ACC_PUBLIC\n Code:\n stack=1, locals=1, args_size=1\n 0: aload_0\n 1: invokespecial #1 // Method java/lang/Object."<init>":()V\n 4: return\n LineNumberTable:\n line 7: 0\n LocalVariableTable:\n Start Length Slot Name Signature\n 0 5 0 this Lcom/zhuhjay/demo3/Demo3_1;\n\n public static void main(java.lang.String[]);\n descriptor: ([Ljava/lang/String;)V\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=2, locals=4, args_size=1\n 0: bipush 10\n 2: istore_1\n 3: ldc #3 // int 32768\n 5: istore_2\n 6: iload_1\n 7: iload_2\n 8: iadd\n 9: istore_3\n 10: getstatic #4 // Field java/lang/System.out:Ljava/io/PrintStream;\n 13: iload_3\n 14: invokevirtual #5 // Method java/io/PrintStream.println:(I)V\n 17: return\n LineNumberTable:\n line 9: 0\n line 10: 3\n line 11: 6\n line 12: 10\n line 13: 17\n LocalVariableTable:\n Start Length Slot Name Signature\n 0 18 0 args [Ljava/lang/String;\n 3 15 1 a I\n 6 12 2 b I\n 10 8 3 c I\n}\nSourceFile: "Demo3_1.java"\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br"),a("span",{staticClass:"line-number"},[s._v("28")]),a("br"),a("span",{staticClass:"line-number"},[s._v("29")]),a("br"),a("span",{staticClass:"line-number"},[s._v("30")]),a("br"),a("span",{staticClass:"line-number"},[s._v("31")]),a("br"),a("span",{staticClass:"line-number"},[s._v("32")]),a("br"),a("span",{staticClass:"line-number"},[s._v("33")]),a("br"),a("span",{staticClass:"line-number"},[s._v("34")]),a("br"),a("span",{staticClass:"line-number"},[s._v("35")]),a("br"),a("span",{staticClass:"line-number"},[s._v("36")]),a("br"),a("span",{staticClass:"line-number"},[s._v("37")]),a("br"),a("span",{staticClass:"line-number"},[s._v("38")]),a("br"),a("span",{staticClass:"line-number"},[s._v("39")]),a("br"),a("span",{staticClass:"line-number"},[s._v("40")]),a("br"),a("span",{staticClass:"line-number"},[s._v("41")]),a("br"),a("span",{staticClass:"line-number"},[s._v("42")]),a("br"),a("span",{staticClass:"line-number"},[s._v("43")]),a("br"),a("span",{staticClass:"line-number"},[s._v("44")]),a("br"),a("span",{staticClass:"line-number"},[s._v("45")]),a("br"),a("span",{staticClass:"line-number"},[s._v("46")]),a("br"),a("span",{staticClass:"line-number"},[s._v("47")]),a("br"),a("span",{staticClass:"line-number"},[s._v("48")]),a("br"),a("span",{staticClass:"line-number"},[s._v("49")]),a("br"),a("span",{staticClass:"line-number"},[s._v("50")]),a("br"),a("span",{staticClass:"line-number"},[s._v("51")]),a("br"),a("span",{staticClass:"line-number"},[s._v("52")]),a("br"),a("span",{staticClass:"line-number"},[s._v("53")]),a("br"),a("span",{staticClass:"line-number"},[s._v("54")]),a("br"),a("span",{staticClass:"line-number"},[s._v("55")]),a("br"),a("span",{staticClass:"line-number"},[s._v("56")]),a("br"),a("span",{staticClass:"line-number"},[s._v("57")]),a("br"),a("span",{staticClass:"line-number"},[s._v("58")]),a("br"),a("span",{staticClass:"line-number"},[s._v("59")]),a("br"),a("span",{staticClass:"line-number"},[s._v("60")]),a("br"),a("span",{staticClass:"line-number"},[s._v("61")]),a("br"),a("span",{staticClass:"line-number"},[s._v("62")]),a("br"),a("span",{staticClass:"line-number"},[s._v("63")]),a("br"),a("span",{staticClass:"line-number"},[s._v("64")]),a("br"),a("span",{staticClass:"line-number"},[s._v("65")]),a("br"),a("span",{staticClass:"line-number"},[s._v("66")]),a("br"),a("span",{staticClass:"line-number"},[s._v("67")]),a("br"),a("span",{staticClass:"line-number"},[s._v("68")]),a("br"),a("span",{staticClass:"line-number"},[s._v("69")]),a("br"),a("span",{staticClass:"line-number"},[s._v("70")]),a("br"),a("span",{staticClass:"line-number"},[s._v("71")]),a("br"),a("span",{staticClass:"line-number"},[s._v("72")]),a("br"),a("span",{staticClass:"line-number"},[s._v("73")]),a("br"),a("span",{staticClass:"line-number"},[s._v("74")]),a("br"),a("span",{staticClass:"line-number"},[s._v("75")]),a("br"),a("span",{staticClass:"line-number"},[s._v("76")]),a("br"),a("span",{staticClass:"line-number"},[s._v("77")]),a("br"),a("span",{staticClass:"line-number"},[s._v("78")]),a("br"),a("span",{staticClass:"line-number"},[s._v("79")]),a("br"),a("span",{staticClass:"line-number"},[s._v("80")]),a("br"),a("span",{staticClass:"line-number"},[s._v("81")]),a("br"),a("span",{staticClass:"line-number"},[s._v("82")]),a("br"),a("span",{staticClass:"line-number"},[s._v("83")]),a("br"),a("span",{staticClass:"line-number"},[s._v("84")]),a("br"),a("span",{staticClass:"line-number"},[s._v("85")]),a("br"),a("span",{staticClass:"line-number"},[s._v("86")]),a("br"),a("span",{staticClass:"line-number"},[s._v("87")]),a("br"),a("span",{staticClass:"line-number"},[s._v("88")]),a("br"),a("span",{staticClass:"line-number"},[s._v("89")]),a("br"),a("span",{staticClass:"line-number"},[s._v("90")]),a("br"),a("span",{staticClass:"line-number"},[s._v("91")]),a("br"),a("span",{staticClass:"line-number"},[s._v("92")]),a("br"),a("span",{staticClass:"line-number"},[s._v("93")]),a("br")])]),a("h4",{attrs:{id:"_3-常量池载入运行时常量池"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-常量池载入运行时常量池"}},[s._v("#")]),s._v(" 3) 常量池载入运行时常量池")]),s._v(" "),a("p",[s._v("JVM 通过类加载器将以上字节码数据读入,将常量池数据存储到运行时常量池(属于方法区的一部分)中")]),s._v(" "),a("ul",[a("li",[s._v("#3 这个数据的来源是 "),a("code",[s._v("Short.MAX_VALUE + 1")]),s._v(",java源码中比较小的数值并不会存储在常量池中,而是与方法的字节码指令存储在一起,一旦超出了 "),a("code",[s._v("Short.MAX_VALUE(32767)")]),s._v(" 就会存储到常量池中。")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670221697470.png",alt:"1670221697470"}}),s._v(" "),a("h4",{attrs:{id:"_4-方法字节码载入方法区"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_4-方法字节码载入方法区"}},[s._v("#")]),s._v(" 4) 方法字节码载入方法区")]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670222538332.png",alt:"1670222538332"}}),s._v(" "),a("h4",{attrs:{id:"_5-main-线程开始运行-分配栈帧内存"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_5-main-线程开始运行-分配栈帧内存"}},[s._v("#")]),s._v(" 5) main 线程开始运行,分配栈帧内存")]),s._v(" "),a("p",[s._v("会根据以下信息来进行栈帧分配,操作数栈深度为2,局部变量表长度为4")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("stack=2, locals=4, args_size=1\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br")])]),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670222781062.png",alt:"1670222781062"}}),s._v(" "),a("h4",{attrs:{id:"_6-执行引擎开始执行字节码"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_6-执行引擎开始执行字节码"}},[s._v("#")]),s._v(" 6) 执行引擎开始执行字节码")]),s._v(" "),a("p",[a("strong",[s._v("bipush 10")])]),s._v(" "),a("ul",[a("li",[s._v("将一个 byte 压入操作数栈(其长度会补齐 4 个字节),类似的指令还有\n"),a("ul",[a("li",[s._v("sipush 将一个 short 压入操作数栈(其长度会补齐 4 个字节)")]),s._v(" "),a("li",[s._v("ldc 将一个 int 压入操作数栈")]),s._v(" "),a("li",[s._v("ldc2_w 将一个 long 压入操作数栈(分两次压入,因为 long 是 8 个字节)")])])]),s._v(" "),a("li",[s._v("这里小的数字都是和字节码指令存在一起,超过 short 范围的数字存入了常量池")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670223128743.png",alt:"1670223128743"}}),s._v(" "),a("p",[a("strong",[s._v("istore_1")])]),s._v(" "),a("ul",[a("li",[s._v("将操作数栈顶数据弹出,存入局部变量表的 slot 1")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670223335018.png",alt:"1670223335018"}}),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670223376535.png",alt:"1670223376535"}}),s._v(" "),a("p",[s._v("以上操作代表源代码的 "),a("code",[s._v("int a = 10;")]),s._v(" 这个赋值操作")]),s._v(" "),a("p",[a("strong",[s._v("ldc #3")])]),s._v(" "),a("ul",[a("li",[s._v("从常量池加载 #3 数据到操作数栈")]),s._v(" "),a("li",[a("strong",[s._v("注意")]),s._v(" "),a("code",[s._v("Short.MAX_VALUE")]),s._v(" 是 32767,所以 "),a("code",[s._v("32768 = Short.MAX_VALUE + 1")]),s._v(" 实际是在编译期间计算好的(常量折叠优化)")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670223577473.png",alt:"1670223577473"}}),s._v(" "),a("p",[a("strong",[s._v("istore_2")])]),s._v(" "),a("ul",[a("li",[s._v("将操作数栈顶数据弹出,存入局部变量表的 slot 2")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670223846251.png",alt:"1670223846251"}}),s._v(" "),a("p",[s._v("以上操作代表源代码的 "),a("code",[s._v("int b = Short.MAX_VALUE + 1;")]),s._v(" 这个赋值操作")]),s._v(" "),a("p",[a("strong",[s._v("iload_1")])]),s._v(" "),a("ul",[a("li",[s._v("将局部变量表中的 slot 1 数据读取复制到操作数栈中")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670223953960.png",alt:"1670223953960"}}),s._v(" "),a("p",[a("strong",[s._v("iload_2")])]),s._v(" "),a("ul",[a("li",[s._v("将局部变量表中的 slot 2 数据读取复制到操作数栈中")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670224060014.png",alt:"1670224060014"}}),s._v(" "),a("p",[a("strong",[s._v("iadd")])]),s._v(" "),a("ul",[a("li",[s._v("将操作数栈中的数据进行相加的操作")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670224223804.png",alt:"1670224223804"}}),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670224265031.png",alt:"1670224265031"}}),s._v(" "),a("p",[a("strong",[s._v("istore_3")])]),s._v(" "),a("ul",[a("li",[s._v("将操作数栈顶数据弹出,存入局部变量表的 slot 3")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670224443009.png",alt:"1670224443009"}}),s._v(" "),a("p",[s._v("以上操作代表源代码的 "),a("code",[s._v("int c = a + b;")]),s._v(" 这个操作")]),s._v(" "),a("p",[a("strong",[s._v("getstatic #4")])]),s._v(" "),a("ul",[a("li",[s._v("从常量池中获取成员变量 #4 找到堆中的对象,将该对象的引用放入到操作数栈中")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670224527319.png",alt:"1670224527319"}}),s._v(" "),a("p",[a("strong",[s._v("iload_3")])]),s._v(" "),a("ul",[a("li",[s._v("将局部变量表中的 slot 3 数据读取复制到操作数栈中")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670224818125.png",alt:"1670224818125"}}),s._v(" "),a("p",[a("strong",[s._v("invokevirtual #5")])]),s._v(" "),a("ul",[a("li",[s._v("找到常量池 #5 项")]),s._v(" "),a("li",[s._v("定位到方法区 "),a("code",[s._v("java/io/PrintStream.println:(I)V")]),s._v(" 方法")]),s._v(" "),a("li",[s._v("生成新的栈帧(分配 locals、stack等,每执行一个方法都会有新的栈帧)")]),s._v(" "),a("li",[s._v("传递参数,执行新栈帧中的字节码")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670225026514.png",alt:"1670225026514"}}),s._v(" "),a("ul",[a("li",[s._v("执行完毕,弹出栈帧")]),s._v(" "),a("li",[s._v("清除 main 操作数栈内容")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670225112947.png",alt:"1670225112947"}}),s._v(" "),a("p",[a("strong",[s._v("return")])]),s._v(" "),a("ul",[a("li",[a("p",[s._v("完成 main 方法调用,弹出 main 栈帧")])]),s._v(" "),a("li",[a("p",[s._v("程序结束")])])]),s._v(" "),a("h3",{attrs:{id:"_2-4-练习-分析i"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-4-练习-分析i"}},[s._v("#")]),s._v(" 2.4 练习 - 分析i++")]),s._v(" "),a("p",[s._v("从字节码角度分析 i++ 相关题目")]),s._v(" "),a("p",[s._v("源码")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("package")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token namespace"}},[s._v("com"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("zhuhjay"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("demo3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_2")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" b "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" a"),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),s._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" a"),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("--")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br")])]),a("p",[s._v("字节码")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("public static void main(java.lang.String[]);\n descriptor: ([Ljava/lang/String;)V\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=2, locals=3, args_size=1\n 0: bipush 10\n 2: istore_1\n 3: iload_1\n 4: iinc 1, 1\n 7: iinc 1, 1\n 10: iload_1\n 11: iadd\n 12: iload_1\n 13: iinc 1, -1\n 16: iadd\n 17: istore_2\n 18: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;\n 21: iload_1\n 22: invokevirtual #3 // Method java/io/PrintStream.println:(I)V\n 25: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;\n 28: iload_2\n 29: invokevirtual #3 // Method java/io/PrintStream.println:(I)V\n 32: return\n LineNumberTable:\n line 9: 0\n line 10: 3\n line 11: 18\n line 12: 25\n line 13: 32\n LocalVariableTable:\n Start Length Slot Name Signature\n 0 33 0 args [Ljava/lang/String;\n 3 30 1 a I\n 18 15 2 b I\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br"),a("span",{staticClass:"line-number"},[s._v("28")]),a("br"),a("span",{staticClass:"line-number"},[s._v("29")]),a("br"),a("span",{staticClass:"line-number"},[s._v("30")]),a("br"),a("span",{staticClass:"line-number"},[s._v("31")]),a("br"),a("span",{staticClass:"line-number"},[s._v("32")]),a("br"),a("span",{staticClass:"line-number"},[s._v("33")]),a("br"),a("span",{staticClass:"line-number"},[s._v("34")]),a("br")])]),a("p",[s._v("分析:")]),s._v(" "),a("ul",[a("li",[a("p",[a("strong",[s._v("注意")]),s._v(" iinc 指令是直接在局部变量 slot 上进行运算")])]),s._v(" "),a("li",[a("p",[s._v("a++ 和 ++a 的区别是 先执行 iload 还是 先执行 iinc")])]),s._v(" "),a("li",[a("p",[s._v("将一个 byte 数值类型 10 压入到操作数栈中")])])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670225735794.png",alt:"1670225735794"}}),s._v(" "),a("ul",[a("li",[s._v("将操作数栈顶数据弹出,存入局部变量表的 slot 1,此时完成了代码 "),a("code",[s._v("int a = 10")]),s._v(" 的操作")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670225834483.png",alt:"1670225834483"}}),s._v(" "),a("ul",[a("li",[s._v("将局部变量表中的 slot 1 的数据读取复制到操作数栈中,"),a("code",[s._v("a++")]),s._v(" 执行顺序是先读取复制,再进行自增的操作")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670225887463.png",alt:"1670225887463"}}),s._v(" "),a("ul",[a("li",[s._v("对局部变量表中的 slot 1 进行长度为 1 的自增,是直接在局部变量表中直接进行操作,而不是在操作数栈中进行")]),s._v(" "),a("li",[s._v("此时局部变量表中的 a 和 操作数栈中的数值不是一个相等的值")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670225973371.png",alt:"1670225973371"}}),s._v(" "),a("ul",[a("li",[s._v("现将进行 "),a("code",[s._v("++a")]),s._v(" 的运算,会先对局部变量表中的 slot 1 中的数值进行自增,而后才将该结果读取复制到操作数栈中")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670226003812.png",alt:"1670226003812"}}),s._v(" "),a("ul",[a("li",[s._v("读取局部变量表中 slot 1 的数值到操作数栈中")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670226078219.png",alt:"1670226078219"}}),s._v(" "),a("ul",[a("li",[s._v("计算完 "),a("code",[s._v("a++")]),s._v(" 和 "),a("code",[s._v("++a")]),s._v(" 过后,操作数栈中已经存在两个数据了,所以会先对操作数栈中的数据进行相加的操作")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670226107200.png",alt:"1670226107200"}}),s._v(" "),a("ul",[a("li",[s._v("现将进行 "),a("code",[s._v("a--")]),s._v(" 的运算,先将局部变量表中 slot 1 读取复制到操作数栈中")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670226176345.png",alt:"1670226176345"}}),s._v(" "),a("ul",[a("li",[s._v("将局部变量表中的 slot 1 进行自减操作")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670226329153.png",alt:"1670226329153"}}),s._v(" "),a("ul",[a("li",[s._v("将操作数栈中的数据进行相加,到此为止 "),a("code",[s._v("a++ + ++a + a--")]),s._v(" 的运算结束")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670226379924.png",alt:"1670226379924"}}),s._v(" "),a("ul",[a("li",[s._v("最后将操作数栈中的数据存放到局部变量表中对应的位置上去")])]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670226433126.png",alt:"1670226433126"}}),s._v(" "),a("h3",{attrs:{id:"_2-5-条件判断指令"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-5-条件判断指令"}},[s._v("#")]),s._v(" 2.5 条件判断指令")]),s._v(" "),a("table",[a("thead",[a("tr",[a("th",[s._v("指令")]),s._v(" "),a("th",[s._v("助记符")]),s._v(" "),a("th",[s._v("含义")])])]),s._v(" "),a("tbody",[a("tr",[a("td",[s._v("0x99")]),s._v(" "),a("td",[s._v("ifeq")]),s._v(" "),a("td",[s._v("判断是否 == 0")])]),s._v(" "),a("tr",[a("td",[s._v("0x9a")]),s._v(" "),a("td",[s._v("ifne")]),s._v(" "),a("td",[s._v("判断是否 != 0")])]),s._v(" "),a("tr",[a("td",[s._v("0x9b")]),s._v(" "),a("td",[s._v("iflt")]),s._v(" "),a("td",[s._v("判断是否 < 0")])]),s._v(" "),a("tr",[a("td",[s._v("0x9c")]),s._v(" "),a("td",[s._v("ifge")]),s._v(" "),a("td",[s._v("判断是否 >= 0")])]),s._v(" "),a("tr",[a("td",[s._v("0x9d")]),s._v(" "),a("td",[s._v("ifgt")]),s._v(" "),a("td",[s._v("判断是否 > 0")])]),s._v(" "),a("tr",[a("td",[s._v("0x9e")]),s._v(" "),a("td",[s._v("ifle")]),s._v(" "),a("td",[s._v("判断是否 <= 0")])]),s._v(" "),a("tr",[a("td",[s._v("0x9f")]),s._v(" "),a("td",[s._v("if_icmpeq")]),s._v(" "),a("td",[s._v("两个int是否 ==")])]),s._v(" "),a("tr",[a("td",[s._v("0xa0")]),s._v(" "),a("td",[s._v("if_icmpne")]),s._v(" "),a("td",[s._v("两个int是否 !=")])]),s._v(" "),a("tr",[a("td",[s._v("0xa1")]),s._v(" "),a("td",[s._v("if_icmplt")]),s._v(" "),a("td",[s._v("两个int是否 <")])]),s._v(" "),a("tr",[a("td",[s._v("0xa2")]),s._v(" "),a("td",[s._v("if_icmpge")]),s._v(" "),a("td",[s._v("两个int是否 >=")])]),s._v(" "),a("tr",[a("td",[s._v("0xa3")]),s._v(" "),a("td",[s._v("if_icmpgt")]),s._v(" "),a("td",[s._v("两个int是否 >")])]),s._v(" "),a("tr",[a("td",[s._v("0xa4")]),s._v(" "),a("td",[s._v("if_icmple")]),s._v(" "),a("td",[s._v("两个int是否 <=")])]),s._v(" "),a("tr",[a("td",[s._v("0xa5")]),s._v(" "),a("td",[s._v("if_acmpeq")]),s._v(" "),a("td",[s._v("两个引用是否 ==")])]),s._v(" "),a("tr",[a("td",[s._v("0xa6")]),s._v(" "),a("td",[s._v("if_acmpne")]),s._v(" "),a("td",[s._v("两个引用是否 !=")])]),s._v(" "),a("tr",[a("td",[s._v("0xc6")]),s._v(" "),a("td",[s._v("ifnull")]),s._v(" "),a("td",[s._v("判断是否 == null")])]),s._v(" "),a("tr",[a("td",[s._v("0xc7")]),s._v(" "),a("td",[s._v("ifnonnull")]),s._v(" "),a("td",[s._v("判断是否 != null")])])])]),s._v(" "),a("ul",[a("li",[a("p",[s._v("几点说明:")]),s._v(" "),a("ul",[a("li",[s._v("byte,short,char 都会按 int 比较,因为操作数栈都是 4 字节")]),s._v(" "),a("li",[s._v("goto 用来进行跳转到指定行号的字节码")])])]),s._v(" "),a("li",[a("p",[s._v("源码")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("package")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token namespace"}},[s._v("com"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("zhuhjay"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("demo3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_3")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("==")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("else")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br")])])]),s._v(" "),a("li",[a("p",[s._v("字节码")]),s._v(" "),a("ul",[a("li",[s._v("比较小的数是通过 "),a("code",[s._v("iconst")]),s._v(" 指令")]),s._v(" "),a("li",[a("code",[s._v("ifne")]),s._v(" 指令判断操作数栈中的两个数值是否不相等,如果不相等,则跳转到序号为 "),a("code",[s._v("12")]),s._v(" 的指令,否则继续往下执行")]),s._v(" "),a("li",[s._v("该程序 if 判断有两个执行路径\n"),a("ul",[a("li",[a("code",[s._v("3 -> 6 -> 8 -> 9 -> 15")]),s._v(":执行到 "),a("code",[s._v("goto")]),s._v(" 指令后会跳转到对应的序号指令继续执行")]),s._v(" "),a("li",[a("code",[s._v("3 -> 12 -> 14 0> 15")]),s._v(":通过了 if 判断跳转到对应的序号指令继续执行")])])])]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("0: iconst_0\n1: istore_1\n2: iload_1\n3: ifne 12\n6: bipush 10\n8: istore_1\n9: goto 15\n12: bipush 20\n14: istore_1\n15: return\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br")])])])]),s._v(" "),a("blockquote",[a("p",[s._v("Tip:")]),s._v(" "),a("p",[s._v("\t以上比较指令中没有 long,float,double 的比较,那么它们要比较怎么办?")]),s._v(" "),a("p",[s._v("参考 "),a("a",{attrs:{href:"https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-6.html#jvms-6.5.lcmp",target:"_blank",rel:"noopener noreferrer"}},[s._v("https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-6.html#jvms-6.5.lcmp"),a("OutboundLink")],1)])]),s._v(" "),a("h3",{attrs:{id:"_2-6-循环控制指令"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-6-循环控制指令"}},[s._v("#")]),s._v(" 2.6 循环控制指令")]),s._v(" "),a("p",[s._v("其实循环控制还是前面介绍的那些指令,例如 while 循环:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("package")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token namespace"}},[s._v("com"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("zhuhjay"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("demo3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_4")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("while")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n a"),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br")])]),a("p",[s._v("字节码,通过指令 "),a("code",[s._v("if_icmpge")]),s._v(" 判断是否大于等于,是则跳出当前 while 循环,否则继续自增")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("0: iconst_0\n1: istore_1\n2: iload_1\n3: bipush 10\n5: if_icmpge 14\n8: iinc 1, 1\n11: goto 2\n14: return\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br")])]),a("p",[s._v("再比如 do while 循环:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("package")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token namespace"}},[s._v("com"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("zhuhjay"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("demo3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_5")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("do")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n a"),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("while")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br")])]),a("p",[s._v("字节码,与 while 循环不同的地方就是,do while 会先进行自增操作,之后才进行判断")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("0: iconst_0\n1: istore_1\n2: iinc 1, 1\n5: iload_1\n6: bipush 10\n8: if_icmplt 2\n11: return\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br")])]),a("p",[s._v("最后再看看 for 循环:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("package")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token namespace"}},[s._v("com"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("zhuhjay"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("demo3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_6")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br")])]),a("p",[s._v("字节码,会发现 for 循环编译后的字节码和 while 循环是"),a("strong",[s._v("一模一样")]),s._v("的")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("0: iconst_0\n1: istore_1\n2: iload_1\n3: bipush 10\n5: if_icmpge 14\n8: iinc 1, 1\n11: goto 2\n14: return\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br")])]),a("h3",{attrs:{id:"_2-7-练习-判断结果"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-7-练习-判断结果"}},[s._v("#")]),s._v(" 2.7 练习 - 判断结果")]),s._v(" "),a("p",[s._v("请从字节码角度分析,下列代码运行的结果:")]),s._v(" "),a("ul",[a("li",[s._v("问题出现在 "),a("code",[s._v("x = x++")]),s._v(",这部分代码的字节码运行流程如下\n"),a("ul",[a("li",[s._v("从局部变量表中先获取 x 的数值并复制到操作数栈中,此时:"),a("code",[s._v("slot x:0; stack x:0")])]),s._v(" "),a("li",[s._v("对局部变量表中的 x 所在的槽位数值自增1,此时:"),a("code",[s._v("slot x:1; stack x:0")])]),s._v(" "),a("li",[s._v("将操作数栈中的值赋值给局部变量表中 x ,此时:"),a("code",[s._v("slot x:0; stack null")])]),s._v(" "),a("li",[s._v("一直重复以上操作,x 的结果永远都是 0")])])]),s._v(" "),a("li",[s._v("若将以上问题代码改为 "),a("code",[s._v("x = ++x")]),s._v(",将不会出现以上的问题")])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("package")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token namespace"}},[s._v("com"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("zhuhjay"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("demo3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_7")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" x "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("while")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n x "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" x"),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n i"),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 0")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br")])]),a("h3",{attrs:{id:"_2-8-构造方法"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-8-构造方法"}},[s._v("#")]),s._v(" 2.8 构造方法")]),s._v(" "),a("h4",{attrs:{id:"_1-clinit-v"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-clinit-v"}},[s._v("#")]),s._v(" 1) "),a("code",[s._v("<clinit>()V")])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_8")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("30")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br")])]),a("p",[s._v("编译器会按从上至下的顺序,收集所有 static 静态代码块和静态成员赋值的代码,合并为一个特殊的方法"),a("code",[s._v("<clinit>()V")]),s._v(" ,该方法会在类加载的初始化阶段被调用")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("static {};\n descriptor: ()V\n flags: ACC_STATIC\n Code:\n stack=1, locals=0, args_size=0\n 0: bipush 10\n 2: putstatic #2 // Field i:I\n 5: bipush 20\n 7: putstatic #2 // Field i:I\n 10: bipush 30\n 12: putstatic #2 // Field i:I\n 15: return\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br")])]),a("h4",{attrs:{id:"_2-init-v"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-init-v"}},[s._v("#")]),s._v(" 2) "),a("code",[s._v("<init>()V")])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_9")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"s1"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n b "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" b "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"s2"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_9")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("b "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_9")]),s._v(" d "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_9")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"s3"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("30")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("d"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\t"),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// s3")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("d"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\t"),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 30")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br")])]),a("p",[s._v("编译器会按从上至下的顺序,收集所有 {} 代码块和成员变量赋值的代码,形成新的构造方法,但原始构造方法内的代码总是在最后")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v('public com.zhuhjay.demo3.Demo3_9(java.lang.String, int);\n descriptor: (Ljava/lang/String;I)V\n flags: ACC_PUBLIC\n Code:\n stack=2, locals=3, args_size=3\n 0: aload_0\n 1: invokespecial #1 // 调用父类的构造方法(Object)\n 4: aload_0\n 5: ldc #2 // <- "s1"\n 7: putfield #3 // -> this.a\n 10: aload_0\n 11: bipush 20\t\t\t\t // <- 20\n 13: putfield #4 // -> this.b\n 16: aload_0\n 17: bipush 10\t\t\t\t // <- 10\n 19: putfield #4 // -> this.b\n 22: aload_0\n 23: ldc #5 // <- "s2"\n 25: putfield #3 // -> this.a\n 28: aload_0\n 29: aload_1\t\t\t\t\t\t\t // <- "s3"\n 30: putfield #3 // -> this.a\n 33: aload_0\n 34: iload_2\t\t\t\t\t\t\t // <- 30\n 35: putfield #4 // -> this.b\n 38: return\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br")])]),a("h3",{attrs:{id:"_2-9-方法调用"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-9-方法调用"}},[s._v("#")]),s._v(" 2.9 方法调用")]),s._v(" "),a("p",[s._v("看一下几种不同的方法调用对应的字节码指令")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_10")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("final")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test4")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_10")]),s._v(" d "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n d"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n d"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n d"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n d"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test4")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test4")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br")])]),a("p",[s._v("字节码")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v('0: new #2 // class com/zhuhjay/demo3/Demo3_10\n3: dup\n4: invokespecial #3 // Method "<init>":()V\n7: astore_1\n8: aload_1\n9: invokespecial #4 // Method test1:()V\n12: aload_1\n13: invokespecial #5 // Method test2:()V\n16: aload_1\n17: invokevirtual #6 // Method test3:()V\n20: aload_1\n21: pop\n22: invokestatic #7 // Method test4:()V\n25: invokestatic #7 // Method test4:()V\n28: return\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br")])]),a("ul",[a("li",[a("p",[a("code",[s._v("new")]),s._v(" 是创建【对象】,给对象分配堆内存,执行成功会将【对象引用】压入操作数栈")])]),s._v(" "),a("li",[a("p",[a("code",[s._v("dup")]),s._v(" 是赋值操作数栈栈顶的内容,本例即为【对象引用】,为什么需要两份引用呢,一个是要配合 "),a("code",[s._v("invokespecial")]),s._v(" 调用该对象的构造方法 "),a("code",[s._v('"<init>":()V')]),s._v(" (会消耗掉栈顶一个引用),另一个要配合 "),a("code",[s._v("astore_1")]),s._v(" 赋值给局部变量")])]),s._v(" "),a("li",[a("p",[s._v("最终方法(final),私有方法(private),构造方法都是由 "),a("code",[s._v("invokespecial")]),s._v(" 指令来调用,属于 静态绑定")])]),s._v(" "),a("li",[a("p",[s._v("普通成员方法是由 "),a("code",[s._v("invokevirtual")]),s._v(" 调用,属于动态绑定,即支持多态成员方法与静态方法调用的另一个区别是,执行方法前是否需要【对象引用】")])]),s._v(" "),a("li",[a("p",[s._v("比较有意思的是 "),a("code",[s._v("d.test4();")]),s._v(" 是通过【对象引用】调用一个静态方法,可以看到在调用 "),a("code",[s._v("invokestatic")]),s._v(" 之前执行了 "),a("code",[s._v("pop")]),s._v(" 指令,把【对象引用】从操作数栈弹掉了")])]),s._v(" "),a("li",[a("p",[s._v("还有一个执行 "),a("code",[s._v("invokespecial")]),s._v(" 的情况是通过 "),a("code",[s._v("super")]),s._v(" 调用父类方法")])])]),s._v(" "),a("h3",{attrs:{id:"_2-10-多态的原理"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-10-多态的原理"}},[s._v("#")]),s._v(" 2.10 多态的原理")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("package")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token namespace"}},[s._v("com"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("zhuhjay"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("demo3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_11")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Animal")]),s._v(" animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("eat")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("toString")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("throws")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("IOException")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Dog")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Cat")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("read")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("abstract")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Animal")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("abstract")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("eat")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[s._v("@Override")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("toString")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"我是"')]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("getClass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("getSimpleName")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Dog")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("extends")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Animal")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[s._v("@Override")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("eat")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"啃骨头"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Cat")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("extends")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Animal")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[s._v("@Override")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("eat")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"吃鱼"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br")])]),a("h4",{attrs:{id:"_1-运行代码"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-运行代码"}},[s._v("#")]),s._v(" 1) 运行代码")]),s._v(" "),a("p",[a("strong",[s._v("注意")]),s._v(":运行代码前需要添加虚拟机参数 "),a("code",[s._v("-XX:-UseCompressedOops -XX:-UseCompressedClassPointers")]),s._v(",禁止指针压缩,省去了地址换算")]),s._v(" "),a("p",[s._v("停在 "),a("code",[s._v("System.in.read()")]),s._v(" 方法上,这时运行 "),a("code",[s._v("jps")]),s._v(" 获取进程 id")]),s._v(" "),a("h4",{attrs:{id:"_2-运行-hsdb-工具"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-运行-hsdb-工具"}},[s._v("#")]),s._v(" 2) 运行 HSDB 工具")]),s._v(" "),a("p",[s._v("进入 JDK 目录,执行命令 "),a("code",[s._v("java -cp ./lib/sa-jdi.jar sun.jvm.hotspot.HSDB")])]),s._v(" "),a("p",[s._v("进入图形界面后 Attach 到对应的 进程id,效果如下")]),s._v(" "),a("img",{staticStyle:{zoom:"50%"},attrs:{src:"/jvm/1670338229940.png",alt:"1670338229940"}}),s._v(" "),a("h4",{attrs:{id:"_3-查找内存中的对象"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-查找内存中的对象"}},[s._v("#")]),s._v(" 3) 查找内存中的对象")]),s._v(" "),a("p",[s._v("打开 "),a("code",[s._v("Tools -> Find Object By Query")]),s._v(" 工具")]),s._v(" "),a("p",[s._v("输入 "),a("code",[s._v("select d from com.zhuhjay.demo3.Dog d")]),s._v(" 并执行,语法同 SQL 一般,查询结果就是在内存中存在的 Dog 对象内存地址。")]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670338644448.png",alt:"1670338644448"}})]),s._v(" "),a("h4",{attrs:{id:"_4-查看对象内存结构"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_4-查看对象内存结构"}},[s._v("#")]),s._v(" 4) 查看对象内存结构")]),s._v(" "),a("p",[s._v("点击超链接可以看到对象的内存结构,此对象没有任何属性,因此只有对象头的 16 字节,前 8 字节是 MarkWord,后 8 字节就是对象的 Class 指针")]),s._v(" "),a("p",[s._v("但目前看不到它的实际地址,在底层是 C++ 的数据结构,可以看到类中的一些数据,子类父类等等,虚引用表长度 "),a("code",[s._v("_vtable_len")])]),s._v(" "),a("img",{staticStyle:{zoom:"80%"},attrs:{src:"/jvm/1670338857348.png",alt:"1670338857348"}}),s._v(" "),a("h4",{attrs:{id:"_5-查看对象的内存地址"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_5-查看对象的内存地址"}},[s._v("#")]),s._v(" 5) 查看对象的内存地址")]),s._v(" "),a("p",[s._v("通过 "),a("code",[s._v("Windows -> Console")]),s._v(" 进入命令行模式,执行 "),a("code",[s._v("mem 0x0000023338896cd0 2")])]),s._v(" "),a("ul",[a("li",[a("code",[s._v("mem")]),s._v(" 有两个参数,参数 1 是对象地址,参数 2 是查看 2 行(即 16 字节)")])]),s._v(" "),a("p",[s._v("在结果中的第二行即为 Class 的内存地址")]),s._v(" "),a("img",{staticStyle:{zoom:"80%"},attrs:{src:"/jvm/1670339471963.png",alt:"1670339471963"}}),s._v(" "),a("h4",{attrs:{id:"_6-查看类的-vtable"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_6-查看类的-vtable"}},[s._v("#")]),s._v(" 6) 查看类的 vtable")]),s._v(" "),a("ul",[a("li",[a("p",[s._v("方法一:"),a("code",[s._v("Alt+R")]),s._v(" 进入 "),a("code",[s._v("Inspector")]),s._v(" 工具,输入刚刚查询到的 Class 内存地址")]),s._v(" "),a("img",{staticStyle:{zoom:"80%"},attrs:{src:"/jvm/1670339740477.png",alt:"1670339740477"}})]),s._v(" "),a("li",[a("p",[s._v("方法二:打开 "),a("code",[s._v("Tools -> Class Browser")]),s._v(" 输入 Dog 查找,也一样可以找到该 Class 对应的内存地址,然后使用方法一进行查询")]),s._v(" "),a("img",{staticStyle:{zoom:"67%"},attrs:{src:"/jvm/1670339913417.png",alt:"1670339913417"}})])]),s._v(" "),a("p",[s._v("无论通过哪种方法,都可以找到 "),a("code",[s._v("Dog Class")]),s._v(" 的 "),a("code",[s._v("vtable")]),s._v(" 长度为 6,意思就是 "),a("code",[s._v("Dog")]),s._v(" 类有 6 个虚方法(多态相关的,final,static 不会列入)")]),s._v(" "),a("p",[s._v("那么这 6 个方法都是谁呢?从 Class 的起始地址开始算,偏移 "),a("code",[s._v("0x1b8")]),s._v(" 就是 "),a("code",[s._v("vtable")]),s._v(" 的起始地址,进行计算得到:")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("0x00000233675d3c90\n\t\t\t 0x1b8 +\n---------------------\n0x00000233675d3e48\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br")])]),a("p",[s._v("然后使用 "),a("code",[s._v("Windows -> Console")]),s._v(" 工具执行命令,就能够得到这 6 个虚方法的入口地址了")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("mem 0x00000233675d3e48 6\n0x00000233675d3e48: 0x00000233671d1b10 \n0x00000233675d3e50: 0x00000233671d15e8 \n0x00000233675d3e58: 0x00000233675d3758 \n0x00000233675d3e60: 0x00000233671d1540 \n0x00000233675d3e68: 0x00000233671d1678 \n0x00000233675d3e70: 0x00000233675d3c38 \n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br")])]),a("h4",{attrs:{id:"_7-验证方法地址"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_7-验证方法地址"}},[s._v("#")]),s._v(" 7) 验证方法地址")]),s._v(" "),a("p",[s._v("通过 "),a("code",[s._v("Tools -> Class Browser")]),s._v(" 查看每个类的方法定义,比较可知每一个地址都对上了查询到的所有虚方法地址")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("Dog - public void eat() @0x00000233675d3c38;\nAnimal - public java.lang.String toString() @0x00000233675d3758;\nObject - protected void finalize() @0x00000233671d1b10;\nObject - public boolean equals(java.lang.Object) @0x00000233671d15e8;\nObject - public native int hashCode() @0x00000233671d1540;\nObject - protected native java.lang.Object clone() @0x00000233671d1678;\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br")])]),a("h4",{attrs:{id:"_8-小结"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_8-小结"}},[s._v("#")]),s._v(" 8) 小结")]),s._v(" "),a("p",[s._v("当执行 "),a("code",[s._v("invokevirtual")]),s._v(" 指令时")]),s._v(" "),a("ol",[a("li",[s._v("先通过栈帧中的对象引用找到对象")]),s._v(" "),a("li",[s._v("分析对象头,找到对象的实际 Class")]),s._v(" "),a("li",[s._v("Class 结构中有 "),a("code",[s._v("vtable")]),s._v(",它在类加载的链接阶段就已经根据方法的重写规则生成好了")]),s._v(" "),a("li",[s._v("查表得到方法的具体地址")]),s._v(" "),a("li",[s._v("执行方法的字节码")])]),s._v(" "),a("h3",{attrs:{id:"_2-11-异常处理"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-11-异常处理"}},[s._v("#")]),s._v(" 2.11 异常处理")]),s._v(" "),a("h4",{attrs:{id:"_1-try-catch"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-try-catch"}},[s._v("#")]),s._v(" 1) try-catch")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_12_1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Exception")]),s._v(" e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br")])]),a("p",[s._v("部分字节码如下")]),s._v(" "),a("ul",[a("li",[s._v("可以看到多出来一个 "),a("code",[s._v("Exception table")]),s._v(" 的结构,"),a("code",[s._v("[from, to)")]),s._v(" 是前闭后开的检测范围,一旦这个范围内的字节码执行出现异常,则通过 "),a("code",[s._v("type")]),s._v(" 匹配异常类型,如果一致,进入 "),a("code",[s._v("target")]),s._v(" 所指示行号")]),s._v(" "),a("li",[s._v("8 行的字节码指令 "),a("code",[s._v("astore_2")]),s._v(" 是将异常对象引用存入局部变量表的 "),a("code",[s._v("slot 2")]),s._v(" 位置,记录异常对象信息")])]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("public static void main(java.lang.String[]);\n descriptor: ([Ljava/lang/String;)V\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=1, locals=3, args_size=1\n 0: iconst_0\n 1: istore_1\n 2: bipush 10\n 4: istore_1\n 5: goto 12\n 8: astore_2\n 9: bipush 20\n 11: istore_1\n 12: return\n Exception table:\n from to target type\n 2 5 8 Class java/lang/Exception\n LineNumberTable: ...\n LocalVariableTable:\n Start Length Slot Name Signature\n 9 3 2 e Ljava/lang/Exception;\n 0 13 0 args [Ljava/lang/String;\n 2 11 1 i I\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br")])]),a("h4",{attrs:{id:"_2-多个-single-catch-块的情况"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-多个-single-catch-块的情况"}},[s._v("#")]),s._v(" 2) 多个 single-catch 块的情况")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_12_2")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArithmeticException")]),s._v(" e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("NullPointerException")]),s._v(" e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("30")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Exception")]),s._v(" e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("40")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br")])]),a("p",[s._v("部分字节码信息如下")]),s._v(" "),a("ul",[a("li",[s._v("因为异常出现时,只能进入 "),a("code",[s._v("Exception table")]),s._v(" 中一个分支,所以局部变量表 "),a("code",[s._v("Slot 2")]),s._v(" 位置被共用")])]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("public static void main(java.lang.String[]);\n descriptor: ([Ljava/lang/String;)V\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=1, locals=3, args_size=1\n 0: iconst_0\n 1: istore_1\n 2: bipush 10\n 4: istore_1\n 5: goto 26\n 8: astore_2\n 9: bipush 20\n 11: istore_1\n 12: goto 26\n 15: astore_2\n 16: bipush 30\n 18: istore_1\n 19: goto 26\n 22: astore_2\n 23: bipush 40\n 25: istore_1\n 26: return\n Exception table:\n from to target type\n 2 5 8 Class java/lang/ArithmeticException\n 2 5 15 Class java/lang/NullPointerException\n 2 5 22 Class java/lang/Exception\n LineNumberTable: ...\n LocalVariableTable:\n Start Length Slot Name Signature\n 9 3 2 e Ljava/lang/ArithmeticException;\n 16 3 2 e Ljava/lang/NullPointerException;\n 23 3 2 e Ljava/lang/Exception;\n 0 27 0 args [Ljava/lang/String;\n 2 25 1 i I\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br"),a("span",{staticClass:"line-number"},[s._v("28")]),a("br"),a("span",{staticClass:"line-number"},[s._v("29")]),a("br"),a("span",{staticClass:"line-number"},[s._v("30")]),a("br"),a("span",{staticClass:"line-number"},[s._v("31")]),a("br"),a("span",{staticClass:"line-number"},[s._v("32")]),a("br"),a("span",{staticClass:"line-number"},[s._v("33")]),a("br"),a("span",{staticClass:"line-number"},[s._v("34")]),a("br"),a("span",{staticClass:"line-number"},[s._v("35")]),a("br")])]),a("h4",{attrs:{id:"_3-multi-catch-的情况"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-multi-catch-的情况"}},[s._v("#")]),s._v(" 3) multi-catch 的情况")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_12_3")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArithmeticException")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("|")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("NullPointerException")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("|")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("NumberFormatException")]),s._v(" e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br")])]),a("p",[s._v("部分字节码如下")]),s._v(" "),a("ul",[a("li",[s._v("将异常入口进行一次收集,局部变量表 "),a("code",[s._v("Slot 2")]),s._v(" 只收集一个,并且是这些异常的父类型")])]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("public static void main(java.lang.String[]);\n descriptor: ([Ljava/lang/String;)V\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=1, locals=3, args_size=1\n 0: iconst_0\n 1: istore_1\n 2: bipush 10\n 4: istore_1\n 5: goto 12\n 8: astore_2\n 9: bipush 20\n 11: istore_1\n 12: return\n Exception table:\n from to target type\n 2 5 8 Class java/lang/ArithmeticException\n 2 5 8 Class java/lang/NullPointerException\n 2 5 8 Class java/lang/NumberFormatException\n LineNumberTable: ...\n LocalVariableTable:\n Start Length Slot Name Signature\n 9 3 2 e Ljava/lang/RuntimeException;\n 0 13 0 args [Ljava/lang/String;\n 2 11 1 i I\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br")])]),a("h4",{attrs:{id:"_4-finally"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_4-finally"}},[s._v("#")]),s._v(" 4) finally")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_12_4")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Exception")]),s._v(" e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("finally")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("30")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br")])]),a("p",[s._v("部分字节码如下")]),s._v(" "),a("ul",[a("li",[s._v("可以看到 finally 中的代码被"),a("strong",[s._v("复制")]),s._v("了 3 份,分别放入 try 流程,catch 流程以及 catch 剩余的异常类型流程")]),s._v(" "),a("li",[s._v("JVM 会自动捕捉其没有被 catch 块捕获的异常,且如果真的捕获到了这部分异常,同样也会执行 finally 中的代码,并且使用 "),a("code",[s._v("athrow")]),s._v(" 指令将异常向外抛出")])]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("public static void main(java.lang.String[]);\n descriptor: ([Ljava/lang/String;)V\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=1, locals=4, args_size=1\n 0: iconst_0\n 1: istore_1\t\t\t// 0 -> i\n 2: bipush 10\t// try ----------------------\n 4: istore_1\t\t\t// 10 -> i\t\t \t\t|\n 5: bipush 30\t// finally \t\t \t\t|\n 7: istore_1\t\t\t// 30 -> i\t\t \t\t|\n 8: goto 27\t// return -------------------\t\n 11: astore_2\t\t\t// catch Exception -> e\t-----\n 12: bipush 20\t// \t\t\t\t\t\t\t|\n 14: istore_1\t\t\t// 20 -> i \t\t\t\t\t|\n 15: bipush 30\t// finally\t\t\t\t\t|\n 17: istore_1\t\t\t// 30 -> i\t\t\t\t\t|\n 18: goto 27\t// return -------------------\n 21: astore_3\t\t\t// catch any -> slot 3 ------\n 22: bipush 30\t// finally \t\t\t\t\t|\n 24: istore_1\t\t\t// 30 -> i\t\t\t\t\t|\n 25: aload_3\t\t\t\t// <- slot 3\t\t\t\t|\n 26: athrow\t\t\t\t// throw --------------------\n 27: return\n Exception table:\n from to target type\n 2 5 11 Class java/lang/Exception\n 2 5 21 any\n 11 15 21 any\n LineNumberTable: ...\n LocalVariableTable:\n Start Length Slot Name Signature\n 12 3 2 e Ljava/lang/Exception;\n 0 28 0 args [Ljava/lang/String;\n 2 26 1 i I\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br"),a("span",{staticClass:"line-number"},[s._v("28")]),a("br"),a("span",{staticClass:"line-number"},[s._v("29")]),a("br"),a("span",{staticClass:"line-number"},[s._v("30")]),a("br"),a("span",{staticClass:"line-number"},[s._v("31")]),a("br"),a("span",{staticClass:"line-number"},[s._v("32")]),a("br"),a("span",{staticClass:"line-number"},[s._v("33")]),a("br"),a("span",{staticClass:"line-number"},[s._v("34")]),a("br"),a("span",{staticClass:"line-number"},[s._v("35")]),a("br")])]),a("h3",{attrs:{id:"_2-12-练习-finally-面试题"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-12-练习-finally-面试题"}},[s._v("#")]),s._v(" 2.12 练习 - finally 面试题")]),s._v(" "),a("h4",{attrs:{id:"_1-finally-出现了-return"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_1-finally-出现了-return"}},[s._v("#")]),s._v(" 1) finally 出现了 return")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_13_1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("finally")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br")])]),a("p",[s._v("部分字节码如下")]),s._v(" "),a("ul",[a("li",[s._v("由于 finally 中的 "),a("code",[s._v("ireturn")]),s._v(" 被插入了所有可能的流程,因此返回结果肯定以 finally 的为准")]),s._v(" "),a("li",[s._v("至于字节码中第 2 行,似乎没啥用,且留个伏笔,看下个例子")]),s._v(" "),a("li",[s._v("跟上例中的 finally 相比,发现没有 "),a("code",[s._v("athrow")]),s._v(" 了,这告诉我们:"),a("strong",[s._v("如果在 finally 中出现了 return,会吞掉异常")])])]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("public static int test();\n descriptor: ()I\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=1, locals=2, args_size=0\n 0: bipush 10\t// <- 10 放入栈顶\n 2: istore_0\t\t\t// 10 -> slot 0 (从栈顶移除)\n 3: bipush 20\t// <- 20 放入栈顶 (finally代码)\n 5: ireturn\t\t\t\t// 返回栈顶 int(20)\n 6: astore_1\t\t\t// catch any -> slot 1\n 7: bipush 20\t// <- 20 放入栈顶 (finally代码)\n 9: ireturn\t\t\t\t// 返回栈顶 int(20)\n Exception table:\n from to target type\n 0 3 6 any\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br")])]),a("p",[s._v("若将案例代码改为如下")]),s._v(" "),a("ul",[a("li",[s._v("制造一个异常 "),a("code",[s._v("int i = 1/0")]),s._v(",运行后发现不会有异常出现,且结果与上个例子相同")])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_13_1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("/")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("finally")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("20")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br")])]),a("h4",{attrs:{id:"_2-finally-对返回值影响"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-finally-对返回值影响"}},[s._v("#")]),s._v(" 2) finally 对返回值影响")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_13_2")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("finally")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("100")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br")])]),a("p",[s._v("部分字节码如下")]),s._v(" "),a("ul",[a("li",[s._v("finally 中不带 return,就可以正常的捕获异常了(从字节码中 "),a("code",[s._v("athrow")]),s._v(" 看出)")])]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("public static int test();\n descriptor: ()I\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=1, locals=3, args_size=0\n 0: iconst_0\t\t\t// <- 0 放入栈顶\n 1: istore_0\t\t\t// 0 -> i\n 2: iload_0\t\t\t\t// <- i(0)\n 3: istore_1\t\t\t// 0 -> slot 1,暂存至 slot 1,目的是为了固定返回值\n 4: bipush 100\t// <- 100 放入栈顶\n 6: istore_0\t\t\t// 100 -> i\n 7: iload_1\t\t\t\t// <- i(0),读取返回值放置栈顶\n 8: ireturn\t\t\t\t// 返回栈顶 i(0)\n 9: astore_2\t\t\t// catch 部分\n 10: bipush 100\n 12: istore_0\n 13: aload_2\n 14: athrow\n Exception table:\n from to target type\n 2 4 9 any\n LineNumberTable: ...\n LocalVariableTable:\n Start Length Slot Name Signature\n 2 13 0 i I\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br")])]),a("h3",{attrs:{id:"_2-13-synchronized"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_2-13-synchronized"}},[s._v("#")]),s._v(" 2.13 synchronized")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Demo3_14")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Object")]),s._v(" lock "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Object")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("synchronized")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("lock"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"ok"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br")])]),a("p",[s._v("部分字节码如下")]),s._v(" "),a("ul",[a("li",[s._v("JVM 会自动给 "),a("code",[s._v("synchronized")]),s._v(" 代码块中的代码进行异常捕获,当捕获到异常或者 "),a("code",[s._v("synchronized")]),s._v(" 代码块运行结束时,都会进行锁的释放,并且锁的释放过程也会进行异常的捕获,确保锁的释放")])]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v('public static void main(java.lang.String[]);\n descriptor: ([Ljava/lang/String;)V\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=2, locals=4, args_size=1\n 0: new #2 // new Object\n 3: dup\t\t\t\t\t\t\t\t // 复制一份,用来初始化\n 4: invokespecial #1 // invokespecial -> <init>:()V\n 7: astore_1\t\t\t\t\t\t // 将 Object 引用 -> lock\n 8: aload_1\t\t\t\t\t\t\t // <- lock (synchronized开始)\n 9: dup\t\t\t\t\t\t\t\t // 复制一份,一个用于加锁指令一个用于解锁指令\n 10: astore_2\t\t\t\t\t\t // 将 Object 引用 -> slot 2\n 11: monitorenter\t\t\t\t\t // 加锁指令\n 12: getstatic #3 // <- System.out\n 15: ldc #4 // <- "ok"\n 17: invokevirtual #5 // Method java/io/PrintStream.println:(Ljava/lang/String;)V\n 20: aload_2\t\t\t\t\t\t\t // <- slot 2(解锁指令使用的 lock引用)\n 21: monitorexit\t\t\t\t\t\t // 解锁指令\n 22: goto 30\n 25: astore_3\t\t\t\t\t\t // catch any -> slot 3\n 26: aload_2\t\t\t\t\t\t\t // <- slot 2(解锁指令使用的 lock引用)\n 27: monitorexit\t\t\t\t\t\t // 解锁指令\n 28: aload_3\n 29: athrow\t\t\t\t\t\t\t // 异常抛出\n 30: return\n Exception table:\n from to target type\n 12 22 25 any\n 25 28 25 any\n LineNumberTable: ...\n LocalVariableTable:\n Start Length Slot Name Signature\n 0 31 0 args [Ljava/lang/String;\n 8 23 1 lock Ljava/lang/Object;\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br"),a("span",{staticClass:"line-number"},[s._v("28")]),a("br"),a("span",{staticClass:"line-number"},[s._v("29")]),a("br"),a("span",{staticClass:"line-number"},[s._v("30")]),a("br"),a("span",{staticClass:"line-number"},[s._v("31")]),a("br"),a("span",{staticClass:"line-number"},[s._v("32")]),a("br"),a("span",{staticClass:"line-number"},[s._v("33")]),a("br"),a("span",{staticClass:"line-number"},[s._v("34")]),a("br")])]),a("blockquote",[a("p",[a("strong",[s._v("注意")]),s._v(":方法级别的 "),a("code",[s._v("synchronized")]),s._v(" 不会在字节码指令中有所体现")])]),s._v(" "),a("h2",{attrs:{id:"_3-编译器处理"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-编译器处理"}},[s._v("#")]),s._v(" 3 编译器处理")]),s._v(" "),a("p",[s._v("所谓的 "),a("code",[s._v("语法糖")]),s._v(" ,其实就是指 java 编译器把 "),a("code",[s._v("*.java")]),s._v(" 源码编译为 "),a("code",[s._v("*.class")]),s._v(" 字节码的过程中,自动生成和转换的一些代码,主要是为了减轻程序员的负担,算是 java 编译器给我们的一个额外福利")]),s._v(" "),a("p",[s._v("注意,以下代码的分析,借助了 "),a("code",[s._v("javap")]),s._v(" 工具,idea 的反编译功能,idea 插件 "),a("code",[s._v("jclasslib")]),s._v(" 等工具。另外, 编译器转换的结果直接就是 class 字节码,只是为了便于阅读,给出了几乎等价 的 java 源码方式,并不是编译器还会转换出中间的 java 源码,切记。")]),s._v(" "),a("h3",{attrs:{id:"_3-1-默认构造器"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-1-默认构造器"}},[s._v("#")]),s._v(" 3.1 默认构造器")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br")])]),a("p",[s._v("编译成class后的代码:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 这个无参构造是编译器帮助我们加上的")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("super")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v('// 即调用父类 Object 的无参构造方法,即调用 java/lang/Object."<init>":()V')]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br")])]),a("h3",{attrs:{id:"_3-2-自动拆装箱"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-2-自动拆装箱"}},[s._v("#")]),s._v(" 3.2 自动拆装箱")]),s._v(" "),a("p",[s._v("这个特性是 "),a("code",[s._v("JDK 5")]),s._v(" 开始加入的:"),a("code",[s._v("代码一")])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy2")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),s._v(" x "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" y "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br")])]),a("p",[s._v("这段代码在 "),a("code",[s._v("JDK 5")]),s._v(" 之前是无法编译通过的,必须改写为:"),a("code",[s._v("代码二")])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy2")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),s._v(" x "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("valueOf")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" y "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("intValue")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br")])]),a("p",[s._v("显然之前版本的代码太麻烦了,需要在基本类型和包装类型直接来回转换(尤其是集合类中操作的都是包装类型),因此这些转换的事情在 "),a("code",[s._v("JDK 5")]),s._v(" 以后都由编译器在编译阶段完成,即 "),a("code",[s._v("代码一")]),s._v(" 都会在编译阶段被转为 "),a("code",[s._v("代码二")])]),s._v(" "),a("h3",{attrs:{id:"_3-3-泛型集合取值"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-3-泛型集合取值"}},[s._v("#")]),s._v(" 3.3 泛型集合取值")]),s._v(" "),a("p",[s._v("泛型也是在 "),a("code",[s._v("JDK 5")]),s._v(" 开始加入的特性,但 java 在编译泛型代码后会执行 "),a("code",[s._v("泛型擦除")]),s._v(" 的动作,即泛型信息在编译为字节码之后就丢失了,实际的类型都当做了 "),a("code",[s._v("Object")]),s._v(" 类型来处理:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy3")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("List")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(">")])]),s._v(" list "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ArrayList")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("<")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(">")])]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("add")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 实际调用的是 List.add(Object e)")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),s._v(" x "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("get")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 实际调用的是 Object obj = List.get(int index);")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br")])]),a("p",[s._v("所以在取值时,编译器真正生成的字节码中,还要额外做一个类型转换的操作:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 需要将 Object 转为 Integer")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),s._v(" x "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("get")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br")])]),a("p",[s._v("如果前面的 x 变量类型修改为 int 基本类型那么最终生成的字节码是:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 需要将 Object 转为 Integer, 并执行拆箱操作")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" x "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("get")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("intValue")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br")])]),a("p",[s._v("擦除的是字节码上的泛型信息,可以看到 "),a("code",[s._v("LocalVariableTypeTable")]),s._v(" 仍然保留了方法参数泛型的信息")]),s._v(" "),a("ul",[a("li",[s._v("JVM 将代码 "),a("code",[s._v("Integer x = list.get(0);")]),s._v(" 通过 "),a("code",[s._v("Object obj = List.get(int index);")]),s._v(" 方式获取出来后,会使用 "),a("code",[s._v("checkcast")]),s._v(" 指令对照泛型信息表来进行类型的转换")])]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v('public static void main(java.lang.String[]);\n descriptor: ([Ljava/lang/String;)V\n flags: ACC_PUBLIC, ACC_STATIC\n Code:\n stack=2, locals=3, args_size=1\n 0: new #2 // class java/util/ArrayList\n 3: dup\n 4: invokespecial #3 // Method java/util/ArrayList."<init>":()V\n 7: astore_1\n 8: aload_1\n 9: bipush 10\n 11: invokestatic #4 // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;\n 14: invokeinterface #5, 2 // InterfaceMethod java/util/List.add:(Ljava/lang/Object;)Z\n 19: pop\n 20: aload_1\n 21: iconst_0\n 22: invokeinterface #6, 2 // InterfaceMethod java/util/List.get:(I)Ljava/lang/Object;\n 27: checkcast #7 // class java/lang/Integer\n 30: astore_2\n 31: return\n LineNumberTable: ...\n LocalVariableTable:\n Start Length Slot Name Signature\n 0 32 0 args [Ljava/lang/String;\n 8 24 1 list Ljava/util/List;\n 31 1 2 x Ljava/lang/Integer;\n LocalVariableTypeTable:\n Start Length Slot Name Signature\n 8 24 1 list Ljava/util/List<Ljava/lang/Integer;>;\n')])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br"),a("span",{staticClass:"line-number"},[s._v("28")]),a("br"),a("span",{staticClass:"line-number"},[s._v("29")]),a("br")])]),a("p",[s._v("使用反射,仍然能够获得这些信息(只能获取到方法参数上和返回值的泛型信息):")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Set")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(">")])]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("test")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("List")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(">")])]),s._v(" list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Map")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Object")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(">")])]),s._v(" map"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("null")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br")])]),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Method")]),s._v(" test "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("getMethod")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"test"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("List")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Map")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Type")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" types "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" test"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("getGenericParameterTypes")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Type")]),s._v(" type "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" types"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("type "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("instanceof")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ParameterizedType")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ParameterizedType")]),s._v(" parameterizedType "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("ParameterizedType")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" type"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"原始类型 - "')]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" parameterizedType"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("getRawType")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Type")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" arguments "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" parameterizedType"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("getActualTypeArguments")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" arguments"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i"),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("printf")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"\\t泛型参数[%d] - %s\\n"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" arguments"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br")])]),a("p",[s._v("输出")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("原始类型 - interface java.util.List\n\t泛型参数[0] - class java.lang.String\n原始类型 - interface java.util.Map\n\t泛型参数[0] - class java.lang.Integer\n\t泛型参数[1] - class java.lang.Object\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br")])]),a("h3",{attrs:{id:"_3-4-可变参数"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-4-可变参数"}},[s._v("#")]),s._v(" 3.4 可变参数")]),s._v(" "),a("p",[s._v("可变参数也是 "),a("code",[s._v("JDK 5")]),s._v(" 开始加入的新特性: 例如:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy4")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" array "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 直接赋值")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("array"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"hello"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"world"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br")])]),a("p",[s._v("可变参数 "),a("code",[s._v("String... args")]),s._v(" 其实是一个 "),a("code",[s._v("String[] args")]),s._v(" ,从代码中的赋值语句中就可以看出来。 同样 java 编译器会在编译期间将上述代码变换为:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy4")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" array "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 直接赋值")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("array"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"hello"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"world"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br")])]),a("blockquote",[a("p",[a("strong",[s._v("注意")]),s._v(" 如果调用了 "),a("code",[s._v("foo()")]),s._v(" 则等价代码为 "),a("code",[s._v("foo(new String[]{})")]),s._v(" ,创建了一个空的数组,而不会传递 "),a("code",[s._v("null")]),s._v(" 进去")])]),s._v(" "),a("h3",{attrs:{id:"_3-5-foreach-循环"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-5-foreach-循环"}},[s._v("#")]),s._v(" 3.5 foreach 循环")]),s._v(" "),a("p",[s._v("仍是 "),a("code",[s._v("JDK 5")]),s._v(" 开始引入的语法糖,数组的循环:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy5_1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" array "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" e "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" array"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br")])]),a("p",[s._v("字节码信息如下")]),s._v(" "),a("ul",[a("li",[s._v("数组赋初值的简化写法也是语法糖")]),s._v(" "),a("li",[s._v("数组的 "),a("code",[s._v("foreach")]),s._v(" 会被编译成 "),a("code",[s._v("fori")])])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy5_1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy5_1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" array "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("<")]),s._v(" array"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("++")]),s._v("i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" e "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" array"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br")])]),a("p",[s._v("而集合的循环:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy5_2")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("List")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(">")])]),s._v(" list "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Arrays")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("asList")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br")])]),a("p",[s._v("实际被编译器转换为对迭代器的调用:")]),s._v(" "),a("ul",[a("li",[s._v("使用迭代器进行遍历(只有实现了 "),a("code",[s._v("Iterable")]),s._v(" 接口的集合才能使用 "),a("code",[s._v("foreach")]),s._v(" 语法糖 )")])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy5_2")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy5_2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("List")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(">")])]),s._v(" list "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Arrays")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("asList")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("3")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("4")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Iterator")]),s._v(" iter "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("iterator")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("while")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("iter"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("hasNext")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),s._v(" e "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v("iter"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("next")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br")])]),a("blockquote",[a("p",[a("strong",[s._v("注意")]),s._v(" foreach 循环写法,能够配合数组,以及所有实现了 "),a("code",[s._v("Iterable")]),s._v(" 接口的集合类一起使用,其 中 "),a("code",[s._v("Iterable")]),s._v(" 用来获取集合的迭代器( "),a("code",[s._v("Iterator")]),s._v(" )")])]),s._v(" "),a("h3",{attrs:{id:"_3-6-switch-字符串"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-6-switch-字符串"}},[s._v("#")]),s._v(" 3.6 switch 字符串")]),s._v(" "),a("p",[s._v("从 "),a("code",[s._v("JDK 7")]),s._v(" 开始,switch 可以作用于字符串和枚举类,这个功能其实也是语法糖,例如:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy6_1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("choose")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("switch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"hello"')]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"h"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("break")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"world"')]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"w"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("break")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br")])]),a("blockquote",[a("p",[a("strong",[s._v("注意")]),s._v(" switch 配合 String 和枚举使用时,变量不能为 "),a("code",[s._v("null")]),s._v(",原因分析完语法糖转换后的代码应当自然清楚")])]),s._v(" "),a("p",[s._v("会被编译器转换为:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy6_1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy6_1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("choose")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("byte")]),s._v(" x "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("-")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("switch")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("hashCode")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("99162322")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// hello 的 hashCode")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("equals")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"hello"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \tx "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("break")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("113318802")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// world 的 hashCode")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("equals")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"world"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \tx "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("switch")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"h"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("break")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"w"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br")])]),a("p",[s._v("可以看到,执行了两遍 switch,第一遍是根据字符串的 "),a("code",[s._v("hashCode")]),s._v(" 和 "),a("code",[s._v("equals")]),s._v(" 将字符串的转换为相应 byte 类型,第二遍才是利用 byte 执行进行比较。")]),s._v(" "),a("p",[s._v("为什么第一遍时必须既比较 "),a("code",[s._v("hashCode")]),s._v(",又利用 "),a("code",[s._v("equals")]),s._v(" 比较呢?"),a("code",[s._v("hashCode")]),s._v(" 是为了提高效率,减少可能的比较;而 "),a("code",[s._v("equals")]),s._v(" 是为了防止 "),a("code",[s._v("hashCode")]),s._v(" 冲突,例如 "),a("code",[s._v("BM")]),s._v(" 和 "),a("code",[s._v("C.")]),s._v(" 这两个字符串的 "),a("code",[s._v("hashCode")]),s._v(" 值都是 2123 ,如果有如下代码:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy6_1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("choose")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("switch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"BM"')]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"h"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("break")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"C."')]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"w"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("break")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br")])]),a("p",[s._v("编译结果为")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy6_1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy6_1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("choose")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("byte")]),s._v(" var2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("-")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("switch")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("hashCode")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("2123")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("equals")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"C."')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n var2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("else")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("equals")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"BM"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n var2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("default")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("switch")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("var2"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"h"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("break")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"w"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br")])]),a("h3",{attrs:{id:"_3-7-switch-枚举"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-7-switch-枚举"}},[s._v("#")]),s._v(" 3.7 switch 枚举")]),s._v(" "),a("p",[s._v("switch 枚举的例子,原始代码")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("enum")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("MALE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("FEMALE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br")])]),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy7")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),s._v(" sex"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("switch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("sex"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("MALE")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"男"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("break")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("FEMALE")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"女"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("break")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br")])]),a("p",[s._v("编译后会生成以下文件")]),s._v(" "),a("ul",[a("li",[s._v("其中 "),a("code",[s._v("Candy7$1.class")]),s._v(" 文件是用来映射枚举类 Sex 的一个静态内部类")])]),s._v(" "),a("p",[a("img",{attrs:{src:"/jvm/1670415162524.png",alt:"1670415162524"}})]),s._v(" "),a("p",[s._v("字节码如下")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("static final int[] $SwitchMap$com$zhuhjay$jit$Sex;\n descriptor: [I\n flags: ACC_STATIC, ACC_FINAL, ACC_SYNTHETIC\n\nstatic {};\n descriptor: ()V\n flags: ACC_STATIC\n Code:\n stack=3, locals=1, args_size=0\n 0: invokestatic #1 // Method com/zhuhjay/jit/Sex.values:()[Lcom/zhuhjay/jit/Sex;\n 3: arraylength\n 4: newarray int\n 6: putstatic #2 // Field $SwitchMap$com$zhuhjay$jit$Sex:[I\n 9: getstatic #2 // Field $SwitchMap$com$zhuhjay$jit$Sex:[I\n 12: getstatic #3 // Field com/zhuhjay/jit/Sex.MALE:Lcom/zhuhjay/jit/Sex;\n 15: invokevirtual #4 // Method com/zhuhjay/jit/Sex.ordinal:()I\n 18: iconst_1\n 19: iastore\n 20: goto 24\n 23: astore_0\n 24: getstatic #2 // Field $SwitchMap$com$zhuhjay$jit$Sex:[I\n 27: getstatic #6 // Field com/zhuhjay/jit/Sex.FEMALE:Lcom/zhuhjay/jit/Sex;\n 30: invokevirtual #4 // Method com/zhuhjay/jit/Sex.ordinal:()I\n 33: iconst_2\n 34: iastore\n 35: goto 39\n 38: astore_0\n 39: return\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br"),a("span",{staticClass:"line-number"},[s._v("28")]),a("br")])]),a("p",[s._v("也就是会生成以下代码")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy7")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("/**\n * 定义一个合成类(仅 jvm 使用,对我们不可见)\n * 用来映射枚举的 ordinal 与数组元素的关系\n * 枚举的 ordinal 表示枚举对象的序号,从 0 开始\n * 即 MALE 的 ordinal()=0,FEMALE 的 ordinal()=1\n */")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy7")]),s._v("$"),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 数组大小即为枚举元素个数,里面存储case用来对比的数字")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("final")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" $"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("SwitchMap")]),s._v("$com$zhuhjay$jit$"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n $"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("SwitchMap")]),s._v("$com$zhuhjay$jit$"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("MALE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("ordinal")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n $"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("SwitchMap")]),s._v("$com$zhuhjay$jit$"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("FEMALE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("ordinal")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),s._v(" sex"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" x "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy7")]),s._v("$"),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1.")]),s._v("$"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("SwitchMap")]),s._v("$com$zhuhjay$jit$"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),s._v("sex"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("ordinal")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("switch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"男"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("break")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("case")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"女"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("break")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br")])]),a("h3",{attrs:{id:"_3-8-枚举类"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-8-枚举类"}},[s._v("#")]),s._v(" 3.8 枚举类")]),s._v(" "),a("p",[a("code",[s._v("JDK 7")]),s._v(" 新增了枚举类,以前面的性别枚举为例")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("enum")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("MALE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("FEMALE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br")])]),a("p",[s._v("转换后的代码如下")]),s._v(" "),a("ul",[a("li",[s._v("继承 "),a("code",[s._v("Enum")]),s._v(" 枚举类")]),s._v(" "),a("li",[a("code",[s._v("final")]),s._v(" 修饰类")]),s._v(" "),a("li",[s._v("实例个数都在本类中创建,并且不可修改,属于常量")]),s._v(" "),a("li",[s._v("私有构造方法,保护枚举类")]),s._v(" "),a("li",[a("code",[s._v("Enum.valueOf(Sex.class, name)")]),s._v(" 底层原理就是 "),a("code",[s._v("Map")]),s._v(",通过键查找对应的枚举")])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("final")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("extends")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Enum")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(">")])]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("final")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("MALE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("final")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("FEMALE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("final")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" $"),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("VALUES")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n \n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("MALE")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"MALE"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("FEMALE")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"FEMALE"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n $"),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("VALUES")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("MALE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("FEMALE")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n \n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" ordinal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("super")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" ordinal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n \n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("values")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" $"),a("span",{pre:!0,attrs:{class:"token constant"}},[s._v("VALUES")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("clone")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n \n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("valueOf")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Enum")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("valueOf")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Sex")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(",")]),s._v(" name"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br")])]),a("h3",{attrs:{id:"_3-9-try-with-resources"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-9-try-with-resources"}},[s._v("#")]),s._v(" 3.9 try-with-resources")]),s._v(" "),a("p",[a("code",[s._v("JDK 7")]),s._v(" 开始新增了对需要关闭的资源处理的特殊语法 "),a("code",[s._v("try-with-resources")]),s._v(":")]),s._v(" "),a("p",[s._v("其中资源对象需要实现 "),a("code",[s._v("AutoCloseable")]),s._v(" 接口,例如 "),a("code",[s._v("InputStream")]),s._v(" 、 "),a("code",[s._v("OutputStream")]),s._v(" 、 "),a("code",[s._v("Connection")]),s._v(" 、 "),a("code",[s._v("Statement")]),s._v(" 、 "),a("code",[s._v("ResultSet")]),s._v(" 等接口都实现了 "),a("code",[s._v("AutoCloseable")]),s._v(" ,使用 "),a("code",[s._v("try-with-resources")]),s._v(" 可以不用写 "),a("code",[s._v("finally")]),s._v(" 语句块,编译器会帮助生成关闭资源代码,例如:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy9")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("InputStream")]),s._v(" is "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("FileInputStream")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"E:\\\\10067\\\\Documents\\\\dist\\\\index.html"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("is"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Exception")]),s._v(" e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("printStackTrace")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br")])]),a("p",[s._v("编译后代码如下")]),s._v(" "),a("ul",[a("li",[s._v("更完整的关流操作,甚至可以保留压制异常 "),a("code",[s._v("var2.addSuppressed(var11);")])])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy9")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy9")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("InputStream")]),s._v(" is "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("FileInputStream")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"E:\\\\10067\\\\Documents\\\\dist\\\\index.html"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Throwable")]),s._v(" var2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("null")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("is"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Throwable")]),s._v(" var12"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// var2 是我们代码出现的异常")]),s._v("\n var2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" var12"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("throw")]),s._v(" var12"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("finally")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("is "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("!=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("null")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 如果我们代码有异常")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("if")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("var2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("!=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("null")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n is"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("close")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Throwable")]),s._v(" var11"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 当关流的时候也出现了异常,那么作为压制异常添加")]),s._v("\n var2"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("addSuppressed")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("var11"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("else")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 我们代码没有异常,关流出现了异常,那么 var14 关流的异常")]),s._v("\n is"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("close")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Exception")]),s._v(" var14"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n var14"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("printStackTrace")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br"),a("span",{staticClass:"line-number"},[s._v("16")]),a("br"),a("span",{staticClass:"line-number"},[s._v("17")]),a("br"),a("span",{staticClass:"line-number"},[s._v("18")]),a("br"),a("span",{staticClass:"line-number"},[s._v("19")]),a("br"),a("span",{staticClass:"line-number"},[s._v("20")]),a("br"),a("span",{staticClass:"line-number"},[s._v("21")]),a("br"),a("span",{staticClass:"line-number"},[s._v("22")]),a("br"),a("span",{staticClass:"line-number"},[s._v("23")]),a("br"),a("span",{staticClass:"line-number"},[s._v("24")]),a("br"),a("span",{staticClass:"line-number"},[s._v("25")]),a("br"),a("span",{staticClass:"line-number"},[s._v("26")]),a("br"),a("span",{staticClass:"line-number"},[s._v("27")]),a("br"),a("span",{staticClass:"line-number"},[s._v("28")]),a("br"),a("span",{staticClass:"line-number"},[s._v("29")]),a("br"),a("span",{staticClass:"line-number"},[s._v("30")]),a("br"),a("span",{staticClass:"line-number"},[s._v("31")]),a("br"),a("span",{staticClass:"line-number"},[s._v("32")]),a("br"),a("span",{staticClass:"line-number"},[s._v("33")]),a("br"),a("span",{staticClass:"line-number"},[s._v("34")]),a("br")])]),a("p",[s._v("为什么要设计一个 "),a("code",[s._v("addSuppressed(Throwable e)")]),s._v(" (添加被压制异常)的方法呢?是为了防止异常信息的丢失(想想 "),a("code",[s._v("try-with-resources")]),s._v(" 生成的 "),a("code",[s._v("fianlly")]),s._v(" 中如果抛出了异常):")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Test1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("try")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("MyResource")]),s._v(" resource "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("MyResource")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("int")]),s._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("/")]),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("catch")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Exception")]),s._v(" e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("printStackTrace")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("MyResource")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("implements")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("AutoCloseable")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[s._v("@Override")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("close")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("throws")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Exception")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("throw")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Exception")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"关流异常"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br"),a("span",{staticClass:"line-number"},[s._v("12")]),a("br"),a("span",{staticClass:"line-number"},[s._v("13")]),a("br"),a("span",{staticClass:"line-number"},[s._v("14")]),a("br"),a("span",{staticClass:"line-number"},[s._v("15")]),a("br")])]),a("p",[s._v("执行以上代码有以下结果,可以发现异常信息被完整的保留了下来")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("java.lang.ArithmeticException: / by zero\n\tat com.zhuhjay.jit.Test1.main(Test1.java:10)\n\tSuppressed: java.lang.Exception: 关流异常\n\t\tat com.zhuhjay.jit.MyResource.close(Test1.java:20)\n\t\tat com.zhuhjay.jit.Test1.main(Test1.java:11)\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br")])]),a("h3",{attrs:{id:"_3-10-方法重写时的桥接方法"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-10-方法重写时的桥接方法"}},[s._v("#")]),s._v(" 3.10 方法重写时的桥接方法")]),s._v(" "),a("p",[s._v("我们都知道,方法重写时对返回值分两种情况:")]),s._v(" "),a("ul",[a("li",[s._v("父子类的返回值完全一致")]),s._v(" "),a("li",[s._v("子类返回值可以是父类返回值的子类(比较绕口,见下面的例子)")])]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("A")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Number")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("m")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("B")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("extends")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("A")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[s._v("@Override")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("m")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br"),a("span",{staticClass:"line-number"},[s._v("11")]),a("br")])]),a("p",[s._v("对于子类,java 编译器会做如下处理:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("B")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("extends")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("A")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Integer")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("m")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 此方法才是真正重写了父类 public Number m() 方法")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" synthetic bridge "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Number")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("m")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 调用 public Integer m()")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("return")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("m")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br")])]),a("p",[s._v("其中桥接方法比较特殊,仅对 java 虚拟机可见,并且与原来的 "),a("code",[s._v("public Integer m()")]),s._v(" 没有命名冲突,可以用下面反射代码来验证:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("for")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Method")]),s._v(" declaredMethod "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v(":")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("B")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("getDeclaredMethods")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("declaredMethod"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br")])]),a("p",[s._v("发现有两个 "),a("code",[s._v("m()")]),s._v(" 方法,证明了字节码中桥接方法的存在")]),s._v(" "),a("div",{staticClass:"language- line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[s._v("public java.lang.Integer com.zhuhjay.jit.B.m()\npublic java.lang.Number com.zhuhjay.jit.B.m()\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br")])]),a("h3",{attrs:{id:"_3-11-匿名内部类"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-11-匿名内部类"}},[s._v("#")]),s._v(" 3.11 匿名内部类")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy11")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Runnable")]),s._v(" runnable "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Runnable")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[s._v("@Override")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("run")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"ok"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br")])]),a("p",[s._v("源代码编译后会生成一个额外的类")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 额外生成的类")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("final")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy11")]),s._v("$"),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("implements")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Runnable")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy11")]),s._v("$"),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("run")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"ok"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br")])]),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy11")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Runnable")]),s._v(" runnable "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy11")]),s._v("$"),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br")])]),a("p",[s._v("引用局部变量的匿名内部类,源代码:")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy11")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("final")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Runnable")]),s._v(" runnable "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Runnable")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token annotation punctuation"}},[s._v("@Override")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("run")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"ok"')]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br")])]),a("p",[s._v("会在额外生成的类中添加一个有参构造方法,通过参数的方式传递给该类的成员变量的存储,后续让方法获取成员变量的信息来达到目的")]),s._v(" "),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// 额外生成的类")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("final")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy11")]),s._v("$"),a("span",{pre:!0,attrs:{class:"token number"}},[s._v("1")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("implements")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Runnable")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("final")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" val$args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy11")]),s._v("$"),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("this")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("val$args "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("run")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"ok"')]),s._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("+")]),s._v(" val$args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(".")]),s._v("length"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br"),a("span",{staticClass:"line-number"},[s._v("6")]),a("br"),a("span",{staticClass:"line-number"},[s._v("7")]),a("br"),a("span",{staticClass:"line-number"},[s._v("8")]),a("br"),a("span",{staticClass:"line-number"},[s._v("9")]),a("br"),a("span",{staticClass:"line-number"},[s._v("10")]),a("br")])]),a("div",{staticClass:"language-java line-numbers-mode"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy11")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("static")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("void")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("final")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("]")]),s._v(" args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n \t"),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Runnable")]),s._v(" runnable "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Candy11")]),s._v("$"),a("span",{pre:!0,attrs:{class:"token function"}},[s._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),s._v("args"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n")])]),s._v(" "),a("div",{staticClass:"line-numbers-wrapper"},[a("span",{staticClass:"line-number"},[s._v("1")]),a("br"),a("span",{staticClass:"line-number"},[s._v("2")]),a("br"),a("span",{staticClass:"line-number"},[s._v("3")]),a("br"),a("span",{staticClass:"line-number"},[s._v("4")]),a("br"),a("span",{staticClass:"line-number"},[s._v("5")]),a("br")])]),a("blockquote",[a("p",[a("strong",[s._v("注意")]),s._v(" 这同时解释了为什么匿名内部类引用局部变量时,局部变量必须是 "),a("code",[s._v("final")]),s._v(" 的:因为在创建 "),a("code",[s._v("Candy11$1")]),s._v(" 对象时,将 "),a("code",[s._v("args")]),s._v(" 的值赋值给了 "),a("code",[s._v("Candy11$1")]),s._v(" 对象的 "),a("code",[s._v("val$args")]),s._v(" 属性,所以 "),a("code",[s._v("args")]),s._v(" 不应该再发生变化,如果变化了,那么 "),a("code",[s._v("val$args")]),s._v(" 属性没有机会跟着一起变化。(当不对变量进行修改时,编译器会将局部变量用 "),a("code",[s._v("final")]),s._v(" 修饰)")])])])}),[],!1,null,null,null);a.default=e.exports}}]); |