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zhuhjay 22e48d9558 build(www): 添加 Drone CI 流水线配置 
- 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
2025-11-01 13:36:00 +08:00

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<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></div> <!----></nav> <ul class="sidebar-links"><li><a href="/blogs/java/java8/java8-1.html" class="sidebar-link">JDK8 特性（一）</a></li><li><a href="/blogs/java/java8/java8-2.html" class="sidebar-link">JDK8 特性（二）</a></li><li><a href="/blogs/java/java8/java8-3.html" class="sidebar-link">JDK8 特性（三）</a></li><li><a href="/blogs/java/java8/java8-4.html" aria-current="page" class="active sidebar-link">JDK8 特性（四）</a></li></ul> </aside> <div class="password-shadow password-wrapper-in" style="display:none;" data-v-59e6cb88 data-v-7dd95ae2><h3 class="title" data-v-59e6cb88>JDK8 特性（四）</h3> <!----> <label id="box" class="inputBox" data-v-59e6cb88><input type="password" value="" data-v-59e6cb88> <span data-v-59e6cb88>Konck! Knock!</span> <button data-v-59e6cb88>OK</button></label> <div class="footer" data-v-59e6cb88><span data-v-59e6cb88><i class="iconfont reco-theme" data-v-59e6cb88></i> <a target="blank" href="https://vuepress-theme-reco.recoluan.com" data-v-59e6cb88>vuePress-theme-reco</a></span> <span data-v-59e6cb88><i class="iconfont reco-copyright" data-v-59e6cb88></i> <a data-v-59e6cb88><span data-v-59e6cb88>ZhuHJay</span>
  
<span data-v-59e6cb88>2021 - </span>
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</a></span></div></div> <div data-v-7dd95ae2><div data-v-7dd95ae2><main class="page"><section style="display:;"><div class="page-title"><h1 class="title">JDK8 特性（四）</h1> <div data-v-8a445198><i class="iconfont reco-account" data-v-8a445198><span data-v-8a445198>ZhuHJay</span></i> <i class="iconfont reco-date" data-v-8a445198><span data-v-8a445198>2022/5/26</span></i> <!----> <i class="tags iconfont reco-tag" data-v-8a445198><span class="tag-item" data-v-8a445198>JDK8</span></i></div></div> <div class="theme-reco-content content__default"><h2 id="_1-optional"><a href="#_1-optional" class="header-anchor">#</a> 1 Optional</h2> <h3 id="_1-1-optional介绍"><a href="#_1-1-optional介绍" class="header-anchor">#</a> 1.1 Optional介绍</h3> <ul><li>Optional是一个没有子类的工具类，Optional是一个可以为null的容器对象。它的作用主要就是为了解决避免Null检查，防止NullPointerException。</li></ul> <h3 id="_1-2-optional基本使用"><a href="#_1-2-optional基本使用" class="header-anchor">#</a> 1.2 Optional基本使用</h3> <ul><li><p>Optional类的创建方式</p> <div class="language-text line-numbers-mode"><pre class="language-text"><code>Optional.of(T t) : 创建一个 Optional 实例, 不能为空
Optional.empty() : 创建一个空的 Optional 实例
Optional.ofNullable(T t):若 t 不为 null,创建 Optional 实例,否则创建空实例
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div></li> <li><p>Optional类的常用方法</p> <div class="language-text line-numbers-mode"><pre class="language-text"><code>isPresent() : 判断是否包含值,包含值返回true，不包含值返回false
get() : 如果Optional有值则将其返回，否则抛出NoSuchElementException
orElse(T t) : 如果调用对象包含值，返回该值，否则返回参数t
orElseGet(Supplier s) :如果调用对象包含值，返回该值，否则返回 s 获取的值
map(Function f): 如果有值对其处理，并返回处理后的Optional，否则返回 Optional.empty()
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div></li></ul> <h3 id="_1-3-optional高级使用"><a href="#_1-3-optional高级使用" class="header-anchor">#</a> 1.3 Optional高级使用</h3> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">OptionalTest</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">ifPresent</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// Optional&lt;User&gt; op = Optional.of(new User(&quot;张三&quot;, 18));</span>
<span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">User</span><span class="token punctuation">&gt;</span></span> op <span class="token operator">=</span> <span class="token class-name">Optional</span><span class="token punctuation">.</span><span class="token function">empty</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 如果存在就做点什么, 没有就不做了</span>
op<span class="token punctuation">.</span><span class="token function">ifPresent</span><span class="token punctuation">(</span>user <span class="token operator">-&gt;</span> <span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>user<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">map</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token class-name">User</span> user <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">User</span><span class="token punctuation">(</span><span class="token string">&quot;迪丽热巴&quot;</span><span class="token punctuation">,</span> <span class="token number">20</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 判断如果存在, 那么就将名字重新拼接</span>
<span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">User</span><span class="token punctuation">&gt;</span></span> optional <span class="token operator">=</span> <span class="token class-name">Optional</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>user<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token function">getNewName</span><span class="token punctuation">(</span>optional<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">private</span> <span class="token class-name">String</span> <span class="token function">getNewName</span><span class="token punctuation">(</span><span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">User</span><span class="token punctuation">&gt;</span></span> optional<span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token keyword">return</span> optional<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token class-name">User</span><span class="token operator">::</span><span class="token function">getUsername</span><span class="token punctuation">)</span>
<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span>str <span class="token operator">-&gt;</span> str<span class="token punctuation">.</span><span class="token function">substring</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token punctuation">.</span><span class="token function">orElse</span><span class="token punctuation">(</span><span class="token string">&quot;null&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br></div></div><h2 id="_2-新的日期时间api"><a href="#_2-新的日期时间api" class="header-anchor">#</a> 2 新的日期时间API</h2> <ul><li>旧版日期时间API存在的问题
<ol><li>设计很差：在<code>java.util</code>和<code>java.sql</code>的包中都有日期类，<code>java.util.Date</code>同时包含日期和时间，而<code>java.sql.Date</code>仅包含日期。此外用于格式化和解析的类在<code>java.text</code>包中定义。</li> <li>非线程安全：<code>java.util.Date</code>是非线程安全的，所有的日期类都是可变的，这是Java日期类最大的问题之一。</li> <li>时区处理麻烦：日期类并不提供国际化，没有时区支持，因此Java引入了<code>java.util.Calendar</code>和 <code>java.util.TimeZone</code>类，但他们同样存在上述所有的问题。</li></ol></li></ul> <h3 id="_2-1-新的日期时间api介绍"><a href="#_2-1-新的日期时间api介绍" class="header-anchor">#</a> 2.1 新的日期时间API介绍</h3> <ul><li><p>JDK 8中增加了一套全新的日期时间API，这套API设计合理，是线程安全的。新的日期及时间API位于 <code>java.time</code>包中，下面是一些关键类。</p> <ul><li>LocalDate ：表示日期，包含年月日，格式为 2019-10-16</li> <li>LocalTime ：表示时间，包含时分秒，格式为 16:38:54.158549300</li> <li>LocalDateTime ：表示日期时间，包含年月日，时分秒，格式为 2018-09-06T15:33:56.750</li> <li>DateTimeFormatter ：日期时间格式化类。</li> <li>Instant：时间戳，表示一个特定的时间瞬间。</li> <li>Duration：用于计算2个时间(LocalTime，时分秒)的距离</li> <li>Period：用于计算2个日期(LocalDate，年月日)的距离</li> <li>ZonedDateTime ：包含时区的时间</li></ul></li> <li><p>Java中使用的历法是ISO 8601日历系统，它是世界民用历法，也就是我们所说的公历。平年有365天，闰年是366天。此外Java 8还提供了4套其他历法，分别是：</p> <ul><li>ThaiBuddhistDate：泰国佛教历</li> <li>MinguoDate：中华民国历</li> <li>JapaneseDate：日本历</li> <li>HijrahDate：伊斯兰历</li></ul></li></ul> <h3 id="_2-2-日期时间类"><a href="#_2-2-日期时间类" class="header-anchor">#</a> 2.2 日期时间类</h3> <ul><li><p>LocalDate、LocalTime、LocalDateTime类的实例是不可变的对象，分别表示使用 ISO-8601 日历系统的日期、时 间、日期和时间。它们提供了简单的日期或时间，并不包含当前的时间信息，也不包含与时区相关的信息。</p></li> <li><p>LocalDate: 获取日期的信息</p></li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">DateTest</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">localDate</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// 创建指定日期</span>
<span class="token class-name">LocalDate</span> localDate <span class="token operator">=</span> <span class="token class-name">LocalDate</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">2022</span><span class="token punctuation">,</span> <span class="token number">11</span><span class="token punctuation">,</span> <span class="token number">11</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;localDate = &quot;</span> <span class="token operator">+</span> localDate<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// localDate = 2022-11-11</span>
<span class="token comment">// 得到当前日期</span>
<span class="token class-name">LocalDate</span> now <span class="token operator">=</span> <span class="token class-name">LocalDate</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;now = &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// now = 2022-05-23</span>
<span class="token comment">// 获取日期信息</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;年: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getYear</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 年: 2022</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;月: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getMonthValue</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 月: 5</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;日: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getDayOfMonth</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 日: 23</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;星期: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getDayOfWeek</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 星期: MONDAY</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br></div></div><ul><li>LocalTime: 获取时间信息</li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">DateTest</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">localTime</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// 得到指定的时间</span>
<span class="token class-name">LocalTime</span> time <span class="token operator">=</span> <span class="token class-name">LocalTime</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">12</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;time = &quot;</span> <span class="token operator">+</span> time<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// time = 12:12:12</span>
<span class="token comment">// 得到当前时间</span>
<span class="token class-name">LocalTime</span> now <span class="token operator">=</span> <span class="token class-name">LocalTime</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;now = &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// now = 11:43:10.495</span>
<span class="token comment">// 获取时间信息</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;小时: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getHour</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 小时: 11</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;分钟: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getMinute</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 分钟: 43</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;秒: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getSecond</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 秒: 10</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;纳秒: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getNano</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 纳秒: 495000000</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br></div></div><ul><li>LocalDateTime: 获取日期时间类型</li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">DateTest</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">localDateTime</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token class-name">LocalDateTime</span> time <span class="token operator">=</span> <span class="token class-name">LocalDateTime</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">2022</span><span class="token punctuation">,</span> <span class="token number">11</span><span class="token punctuation">,</span> <span class="token number">11</span><span class="token punctuation">,</span> <span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">12</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;time = &quot;</span> <span class="token operator">+</span> time<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// time = 2022-11-11T12:12:12</span>
<span class="token class-name">LocalDateTime</span> now <span class="token operator">=</span> <span class="token class-name">LocalDateTime</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;now = &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// now = 2022-05-23T11:47:29.308</span>
<span class="token comment">// 获取日期信息</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;年: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getYear</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 年: 2022</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;月: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getMonthValue</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 月: 5</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;日: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getDayOfMonth</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 日: 23</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;时: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getHour</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 时: 11</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;分: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getMinute</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 分: 47</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;秒: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getSecond</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 秒: 29</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;纳秒: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">getNano</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 纳秒: 308000000</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br></div></div><ul><li>对日期时间的修改，对已存在的LocalDate对象，创建它的修改版，最简单的方式是使用withAttribute方法。 withAttribute方法会创建对象的一个副本，并按照需要修改它的属性。以下所有的方法都返回了一个修改属性的对象，他们不会影响原来的对象。</li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">DateTest</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">localDateTimeUpdate</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token class-name">LocalDateTime</span> now <span class="token operator">=</span> <span class="token class-name">LocalDateTime</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;now = &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// now = 2022-05-23T12:47:18.640</span>
<span class="token comment">// 修改年份, 每份修改后的数据都是一个新的对象, 不会与原对象冲突</span>
<span class="token class-name">LocalDateTime</span> setYear <span class="token operator">=</span> now<span class="token punctuation">.</span><span class="token function">withYear</span><span class="token punctuation">(</span><span class="token number">2025</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;修改年份后 = &quot;</span> <span class="token operator">+</span> setYear<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 修改年份后 = 2025-05-23T12:47:18.640</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;setYear == now? &quot;</span> <span class="token operator">+</span> <span class="token punctuation">(</span>setYear <span class="token operator">==</span> now<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// setYear == now? false</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;修改月份: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">withMonth</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 修改月份: 2022-01-23T12:47:18.640</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;修改日: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">withDayOfMonth</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 修改日: 2022-05-01T12:47:18.640</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;修改小时: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">withMonth</span><span class="token punctuation">(</span><span class="token number">12</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 修改小时: 2022-12-23T12:47:18.640</span>
<span class="token comment">// 在当前对象的基础上加上或减去指定的时间</span>
<span class="token class-name">LocalDateTime</span> localDateTime <span class="token operator">=</span> now<span class="token punctuation">.</span><span class="token function">plusDays</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;五天后: &quot;</span> <span class="token operator">+</span> localDateTime<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 五天后: 2022-05-28T12:47:18.640</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;10年后: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">plusYears</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 10年后: 2032-05-23T12:47:18.640</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;20年后: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">plusYears</span><span class="token punctuation">(</span><span class="token number">20</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 20年后: 2042-05-23T12:47:18.640</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;3个月前: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">minusMonths</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 3个月前: 2022-02-23T12:47:18.640</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;3分钟前: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">minusMinutes</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 3分钟前: 2022-05-23T12:44:18.640</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br></div></div><ul><li>日期比较</li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">DateTest</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">dateEqual</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// 在JDK8中，LocalDate类中使用isBefore()、isAfter()、equals()方法来比较两个日期，可直接进行比较。</span>
<span class="token class-name">LocalDate</span> now <span class="token operator">=</span> <span class="token class-name">LocalDate</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">LocalDate</span> date <span class="token operator">=</span> <span class="token class-name">LocalDate</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">2011</span><span class="token punctuation">,</span> <span class="token number">11</span><span class="token punctuation">,</span> <span class="token number">11</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>now<span class="token punctuation">.</span><span class="token function">isBefore</span><span class="token punctuation">(</span>date<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>date<span class="token punctuation">.</span><span class="token function">isBefore</span><span class="token punctuation">(</span>now<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><h3 id="_2-3-日期格式化与解析"><a href="#_2-3-日期格式化与解析" class="header-anchor">#</a> 2.3 日期格式化与解析</h3> <ul><li>通过<code>java.time.format.DateTimeFormatter</code>类可以进行日期时间解析与格式化。</li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">DateTest</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">dateFormatAndParse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// 获得当前的日期</span>
<span class="token class-name">LocalDateTime</span> now <span class="token operator">=</span> <span class="token class-name">LocalDateTime</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 自定义日期格式</span>
<span class="token class-name">DateTimeFormatter</span> dateTimeFormatter <span class="token operator">=</span> <span class="token class-name">DateTimeFormatter</span><span class="token punctuation">.</span><span class="token function">ofPattern</span><span class="token punctuation">(</span><span class="token string">&quot;yyyy.MM.dd &amp; HH:mm:ss&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 将日期转换为对应的格式</span>
<span class="token class-name">String</span> format <span class="token operator">=</span> dateTimeFormatter<span class="token punctuation">.</span><span class="token function">format</span><span class="token punctuation">(</span>now<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;format = &quot;</span> <span class="token operator">+</span> format<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 将字符串解析为时间</span>
<span class="token class-name">LocalDateTime</span> time <span class="token operator">=</span> <span class="token class-name">LocalDateTime</span><span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span>format<span class="token punctuation">,</span> dateTimeFormatter<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;time = &quot;</span> <span class="token operator">+</span> time<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br></div></div><h3 id="_2-4-instant类"><a href="#_2-4-instant类" class="header-anchor">#</a> 2.4 Instant类</h3> <ul><li>Instant 时间戳/时间线，内部保存了从1970年1月1日 00:00:00以来的秒和纳秒。</li> <li>只能操作秒以下的级别, 用来程序做一些统计的类, 比如说计算运行时间等, 不是给用户使用的</li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">InstantTest</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">instant</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token class-name">Instant</span> now <span class="token operator">=</span> <span class="token class-name">Instant</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;当前时间戳 = &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 获取从1970 01 01 00:00:00的秒</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>now<span class="token punctuation">.</span><span class="token function">getNano</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>now<span class="token punctuation">.</span><span class="token function">getEpochSecond</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>now<span class="token punctuation">.</span><span class="token function">toEpochMilli</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;5s以后: &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">.</span><span class="token function">plusSeconds</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Instant</span> instant <span class="token operator">=</span> <span class="token class-name">Instant</span><span class="token punctuation">.</span><span class="token function">ofEpochSecond</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;instant = &quot;</span> <span class="token operator">+</span> instant<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br></div></div><h3 id="_2-5-计算日期时间差的类"><a href="#_2-5-计算日期时间差的类" class="header-anchor">#</a> 2.5 计算日期时间差的类</h3> <ul><li><p>Duration/Period类: 计算日期时间差。</p> <ol><li>Duration：用于计算2个时间(LocalTime，时分秒)的距离</li> <li>Period：用于计算2个日期(LocalDate，年月日)的距离</li></ol></li> <li><p>注意: 两个类的计算都是第二个参数减去第一个参数, 所以当参数对调时会产生负数的情况</p></li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">DifferenceDateTest</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// 获取当前时间</span>
<span class="token class-name">LocalTime</span> now <span class="token operator">=</span> <span class="token class-name">LocalTime</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">LocalTime</span> of <span class="token operator">=</span> <span class="token class-name">LocalTime</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">12</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 使用Duration计算时间的间隔</span>
<span class="token class-name">Duration</span> duration <span class="token operator">=</span> <span class="token class-name">Duration</span><span class="token punctuation">.</span><span class="token function">between</span><span class="token punctuation">(</span>of<span class="token punctuation">,</span> now<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;相差的天数&quot;</span> <span class="token operator">+</span> duration<span class="token punctuation">.</span><span class="token function">toDays</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;相差的小时数&quot;</span> <span class="token operator">+</span> duration<span class="token punctuation">.</span><span class="token function">toHours</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;相差的分钟数&quot;</span> <span class="token operator">+</span> duration<span class="token punctuation">.</span><span class="token function">toMinutes</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;相差的秒数&quot;</span> <span class="token operator">+</span> duration<span class="token punctuation">.</span><span class="token function">toMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 获取当前的日期</span>
<span class="token class-name">LocalDate</span> date <span class="token operator">=</span> <span class="token class-name">LocalDate</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">LocalDate</span> localDate <span class="token operator">=</span> <span class="token class-name">LocalDate</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">2021</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 使用Period计算日期的间隔</span>
<span class="token class-name">Period</span> period <span class="token operator">=</span> <span class="token class-name">Period</span><span class="token punctuation">.</span><span class="token function">between</span><span class="token punctuation">(</span>localDate<span class="token punctuation">,</span> date<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;相差的年&quot;</span> <span class="token operator">+</span> period<span class="token punctuation">.</span><span class="token function">getYears</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;相差的月&quot;</span> <span class="token operator">+</span> period<span class="token punctuation">.</span><span class="token function">getMonths</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;相差的日&quot;</span> <span class="token operator">+</span> period<span class="token punctuation">.</span><span class="token function">getDays</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br></div></div><h3 id="_2-6-时间校正器"><a href="#_2-6-时间校正器" class="header-anchor">#</a> 2.6 时间校正器</h3> <ul><li>有时我们可能需要获取例如：将日期调整到“下一个月的第一天”等操作。可以通过时间校正器来进行。
<ul><li>TemporalAdjuster : 时间校正器。</li> <li>TemporalAdjusters : 该类通过静态方法提供了大量的常用TemporalAdjuster的实现。</li></ul></li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Demo</span><span class="token punctuation">{</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">temporalAdjuster</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token class-name">LocalDateTime</span> now <span class="token operator">=</span> <span class="token class-name">LocalDateTime</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 自定义时间调整器</span>
<span class="token class-name">LocalDateTime</span> <span class="token keyword">with</span> <span class="token operator">=</span> now<span class="token punctuation">.</span><span class="token keyword">with</span><span class="token punctuation">(</span>temporal <span class="token operator">-&gt;</span> <span class="token punctuation">{</span>
<span class="token class-name">LocalDateTime</span> dateTime <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">LocalDateTime</span><span class="token punctuation">)</span> temporal<span class="token punctuation">;</span>
<span class="token comment">// 修改到下个月1号</span>
<span class="token keyword">return</span> dateTime<span class="token punctuation">.</span><span class="token function">plusMonths</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">withDayOfMonth</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;with = &quot;</span> <span class="token operator">+</span> <span class="token keyword">with</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div><h3 id="_2-7-设置日期时间的时区"><a href="#_2-7-设置日期时间的时区" class="header-anchor">#</a> 2.7 设置日期时间的时区</h3> <ul><li>Java8 中加入了对时区的支持，LocalDate、LocalTime、LocalDateTime是不带时区的，带时区的日期时间类分别为：ZonedDate、ZonedTime、ZonedDateTime。</li> <li>其中每个时区都对应着ID，ID的格式为 “区域/城市” 。例如 ：Asia/Shanghai 等。</li> <li>ZoneId：该类中包含了所有的时区信息。</li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Demo</span><span class="token punctuation">{</span>
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// 获取所有的时区ID</span>
<span class="token class-name">ZoneId</span><span class="token punctuation">.</span><span class="token function">getAvailableZoneIds</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 不带时区获取计算机的当前时间</span>
<span class="token comment">// 中国默认时区东八区, 比标准时间快8h</span>
<span class="token class-name">LocalDateTime</span> now <span class="token operator">=</span> <span class="token class-name">LocalDateTime</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;now = &quot;</span> <span class="token operator">+</span> now<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 操作带时区的类</span>
<span class="token comment">// 创建世界标准时间, 不带参数则使用计算机默认的时区</span>
<span class="token class-name">ZonedDateTime</span> zonedDateTime <span class="token operator">=</span> <span class="token class-name">ZonedDateTime</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token class-name">Clock</span><span class="token punctuation">.</span><span class="token function">systemUTC</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;zonedDateTime = &quot;</span> <span class="token operator">+</span> zonedDateTime<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;指定时区获取时间: &quot;</span> <span class="token operator">+</span> <span class="token class-name">ZonedDateTime</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token class-name">ZoneId</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token string">&quot;Europe/London&quot;</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br></div></div><h3 id="_2-8-小结"><a href="#_2-8-小结" class="header-anchor">#</a> 2.8 小结</h3> <ul><li><p>详细学习了新的日期是时间相关类，LocalDate表示日期,包含年月日,LocalTime表示时间,包含时分 秒,<code>LocalDateTime = LocalDate + LocalTime</code>,时间的格式化和解析,通过DateTimeFormatter类型进行.</p></li> <li><p>学习了Instant类,方便操作秒和纳秒,一般是给程序使用的.学习Duration/Period计算日期或时间的距离,还使用时间调整器方便的调整时间,学习了带时区的3个类ZoneDate/ZoneTime/ZoneDateTime</p></li> <li><p>JDK 8新的日期和时间API的优势：</p> <ol><li>新版的日期和时间API中，日期和时间对象是不可变的。操纵的日期不会影响老值，而是新生成一个实例。</li> <li>新的API提供了两种不同的时间表示方式，有效地区分了人和机器的不同需求。</li> <li>TemporalAdjuster可以更精确的操纵日期，还可以自定义日期调整器。</li> <li>是线程安全的</li></ol></li></ul> <h2 id="_3-重复注解与类型注释"><a href="#_3-重复注解与类型注释" class="header-anchor">#</a> 3 重复注解与类型注释</h2> <h3 id="_3-1-重复注解的使用"><a href="#_3-1-重复注解的使用" class="header-anchor">#</a> 3.1 重复注解的使用</h3> <ul><li><p>自从Java 5中引入注解以来，注解开始变得非常流行，并在各个框架和项目中被广泛使用。不过注解有一个很大的限制是：在同一个地方不能多次使用同一个注解。JDK 8引入了重复注解的概念，允许在同一个地方多次使用同一个注解。在JDK 8中使用<code>@Repeatable</code>注解定义重复注解。</p></li> <li><p>重复注解的使用步骤：</p> <ol><li>定义重复的注解容器注解</li> <li>定义一个可以重复的注解</li> <li>配置多个重复的注解</li> <li>解析得到指定注解</li></ol></li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token comment">/** 3. 配置多个重复的注解 **/</span>
<span class="token annotation punctuation">@MyTest</span><span class="token punctuation">(</span><span class="token string">&quot;AAA&quot;</span><span class="token punctuation">)</span>
<span class="token annotation punctuation">@MyTest</span><span class="token punctuation">(</span><span class="token string">&quot;BBB&quot;</span><span class="token punctuation">)</span>
<span class="token annotation punctuation">@MyTest</span><span class="token punctuation">(</span><span class="token string">&quot;CCC&quot;</span><span class="token punctuation">)</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">RepeatableTest</span> <span class="token punctuation">{</span>
<span class="token comment">/** 3. 配置多个重复的注解 **/</span>
<span class="token annotation punctuation">@Test</span>
<span class="token annotation punctuation">@MyTest</span><span class="token punctuation">(</span><span class="token string">&quot;DD&quot;</span><span class="token punctuation">)</span>
<span class="token annotation punctuation">@MyTest</span><span class="token punctuation">(</span><span class="token string">&quot;EE&quot;</span><span class="token punctuation">)</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">NoSuchMethodException</span> <span class="token punctuation">{</span>
<span class="token comment">// 4. 解析得到指定注解</span>
<span class="token comment">// getAnnotationsByType是新增API用来获取重复注解的</span>
<span class="token comment">// 获取类上的注解</span>
<span class="token class-name">MyTest</span><span class="token punctuation">[</span><span class="token punctuation">]</span> annotation <span class="token operator">=</span> <span class="token class-name">RepeatableTest</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">.</span><span class="token function">getAnnotationsByType</span><span class="token punctuation">(</span><span class="token class-name">MyTest</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token class-name">MyTest</span> myTest <span class="token operator">:</span> annotation<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;myTest = &quot;</span> <span class="token operator">+</span> myTest<span class="token punctuation">.</span><span class="token function">value</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">// 获取方法上的注解</span>
<span class="token class-name">MyTest</span><span class="token punctuation">[</span><span class="token punctuation">]</span> tests <span class="token operator">=</span> <span class="token class-name">RepeatableTest</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">.</span><span class="token function">getMethod</span><span class="token punctuation">(</span><span class="token string">&quot;test&quot;</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getAnnotationsByType</span><span class="token punctuation">(</span><span class="token class-name">MyTest</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token class-name">MyTest</span> myTest <span class="token operator">:</span> tests<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">&quot;myTest = &quot;</span> <span class="token operator">+</span> myTest<span class="token punctuation">.</span><span class="token function">value</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token comment">/**
* 1. 定义重复的注解容器注解
*/</span>
<span class="token annotation punctuation">@Retention</span><span class="token punctuation">(</span><span class="token class-name">RetentionPolicy</span><span class="token punctuation">.</span><span class="token constant">RUNTIME</span><span class="token punctuation">)</span>
<span class="token annotation punctuation">@interface</span> <span class="token class-name">MyTests</span><span class="token punctuation">{</span>
<span class="token class-name">MyTest</span><span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token function">value</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">/**
* 2. 定义一个可以重复的注解
*/</span>
<span class="token annotation punctuation">@Retention</span><span class="token punctuation">(</span><span class="token class-name">RetentionPolicy</span><span class="token punctuation">.</span><span class="token constant">RUNTIME</span><span class="token punctuation">)</span>
<span class="token annotation punctuation">@Repeatable</span><span class="token punctuation">(</span><span class="token class-name">MyTests</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span>
<span class="token annotation punctuation">@interface</span> <span class="token class-name">MyTest</span><span class="token punctuation">{</span>
<span class="token class-name">String</span> <span class="token function">value</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br></div></div><h3 id="_3-2-类型注解的使用"><a href="#_3-2-类型注解的使用" class="header-anchor">#</a> 3.2 类型注解的使用</h3> <ul><li>JDK 8为@Target元注解新增了两种类型：TYPE_PARAMETER，TYPE_USE 。
<ul><li>TYPE_PARAMETER ：表示该注解能写在类型参数的声明语句中。</li> <li>TYPE_USE ：表示注解可以再任何用到类型的地方使用。</li></ul></li></ul> <div class="language-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">TypeAnnotationDemo</span><span class="token operator">&lt;</span><span class="token annotation punctuation">@TypeParam</span> <span class="token class-name">T</span><span class="token operator">&gt;</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span> <span class="token annotation punctuation">@NotNull</span> <span class="token keyword">int</span> one <span class="token operator">=</span> <span class="token number">10</span><span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token operator">&lt;</span><span class="token annotation punctuation">@TypeParam</span> <span class="token class-name">E</span> <span class="token keyword">extends</span> <span class="token class-name">Integer</span><span class="token operator">&gt;</span> <span class="token keyword">void</span> <span class="token function">test</span><span class="token punctuation">(</span><span class="token annotation punctuation">@NotNull</span> <span class="token class-name">E</span> ele<span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@NotNull</span> <span class="token keyword">int</span> x <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span>
<span class="token annotation punctuation">@NotNull</span> <span class="token class-name">String</span> str <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token annotation punctuation">@NotNull</span> <span class="token class-name">String</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token comment">/**
* 该注解能用到类型前面
*/</span>
<span class="token annotation punctuation">@Target</span><span class="token punctuation">(</span><span class="token class-name">ElementType</span><span class="token punctuation">.</span><span class="token constant">TYPE_USE</span><span class="token punctuation">)</span>
<span class="token annotation punctuation">@interface</span> <span class="token class-name">NotNull</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
<span class="token comment">/**
* 该注解能写在泛型上
*/</span>
<span class="token annotation punctuation">@Target</span><span class="token punctuation">(</span><span class="token class-name">ElementType</span><span class="token punctuation">.</span><span class="token constant">TYPE_PARAMETER</span><span class="token punctuation">)</span>
<span class="token annotation punctuation">@interface</span> <span class="token class-name">TypeParam</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br></div></div></div></section> <footer class="page-edit"><!----> <!----></footer> <div class="page-nav"><p class="inner"><span class="prev"><a href="/blogs/java/java8/java8-3.html" class="prev">
JDK8 特性（三）
</a></span> <!----></p></div> <div class="comments-wrapper"><!----></div></main></div> <!----></div> <ul class="sub-sidebar sub-sidebar-wrapper" style="width:12rem;" data-v-b57cc07c data-v-7dd95ae2><li class="level-2" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_1-optional" class="sidebar-link reco-side-_1-optional" data-v-b57cc07c>1 Optional</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_1-1-optional介绍" class="sidebar-link reco-side-_1-1-optional介绍" data-v-b57cc07c>1.1 Optional介绍</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_1-2-optional基本使用" class="sidebar-link reco-side-_1-2-optional基本使用" data-v-b57cc07c>1.2 Optional基本使用</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_1-3-optional高级使用" class="sidebar-link reco-side-_1-3-optional高级使用" data-v-b57cc07c>1.3 Optional高级使用</a></li><li class="level-2" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_2-新的日期时间api" class="sidebar-link reco-side-_2-新的日期时间api" data-v-b57cc07c>2 新的日期时间API</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_2-1-新的日期时间api介绍" class="sidebar-link reco-side-_2-1-新的日期时间api介绍" data-v-b57cc07c>2.1 新的日期时间API介绍</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_2-2-日期时间类" class="sidebar-link reco-side-_2-2-日期时间类" data-v-b57cc07c>2.2 日期时间类</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_2-3-日期格式化与解析" class="sidebar-link reco-side-_2-3-日期格式化与解析" data-v-b57cc07c>2.3 日期格式化与解析</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_2-4-instant类" class="sidebar-link reco-side-_2-4-instant类" data-v-b57cc07c>2.4 Instant类</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_2-5-计算日期时间差的类" class="sidebar-link reco-side-_2-5-计算日期时间差的类" data-v-b57cc07c>2.5 计算日期时间差的类</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_2-6-时间校正器" class="sidebar-link reco-side-_2-6-时间校正器" data-v-b57cc07c>2.6 时间校正器</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_2-7-设置日期时间的时区" class="sidebar-link reco-side-_2-7-设置日期时间的时区" data-v-b57cc07c>2.7 设置日期时间的时区</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_2-8-小结" class="sidebar-link reco-side-_2-8-小结" data-v-b57cc07c>2.8 小结</a></li><li class="level-2" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_3-重复注解与类型注释" class="sidebar-link reco-side-_3-重复注解与类型注释" data-v-b57cc07c>3 重复注解与类型注释</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_3-1-重复注解的使用" class="sidebar-link reco-side-_3-1-重复注解的使用" data-v-b57cc07c>3.1 重复注解的使用</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-4.html#_3-2-类型注解的使用" class="sidebar-link reco-side-_3-2-类型注解的使用" 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