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
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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" aria-current="page" class="active 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" class="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（二）</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>
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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（二）</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>2022/5/24</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-stream流"><a href="#_1-stream流" class="header-anchor">#</a> 1 Stream流</h2> <h3 id="_1-1-集合处理数据的弊端"><a href="#_1-1-集合处理数据的弊端" class="header-anchor">#</a> 1.1 集合处理数据的弊端</h3> <ul><li><p>案例引入:</p> <ol><li>首先筛选所有姓张的人；</li> <li>然后筛选名字有三个字的人；</li> <li>最后进行对结果进行打印输出。</li></ol></li> <li><p>传统实现</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">StreamDemo</span> <span class="token punctuation">{</span>
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<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>
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<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// 1. 首先筛选所有姓张的人；</span>
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<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> zhangList <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token class-name">String</span> name <span class="token operator">:</span> list<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">if</span><span class="token punctuation">(</span>name<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span><span class="token string">"张"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
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zhangList<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span>name<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token comment">// 2. 然后筛选名字有三个字的人；</span>
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<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> threeList <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token class-name">String</span> name <span class="token operator">:</span> zhangList<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">if</span><span class="token punctuation">(</span>name<span class="token punctuation">.</span><span class="token function">length</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
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threeList<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span>name<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token comment">// 3. 最后进行对结果进行打印输出。</span>
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<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token class-name">String</span> name <span class="token operator">:</span> threeList<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<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>name<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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</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>Stream流式实现</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">StreamDemo</span> <span class="token punctuation">{</span>
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<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>
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||||
<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">// 1. 首先筛选所有姓张的人; 2. 然后筛选名字有三个字的人; 3. 最后进行对结果进行打印输出</span>
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list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
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||||
<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>str <span class="token operator">-></span> str<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span><span class="token string">"张"</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
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||||
<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>str <span class="token operator">-></span> str<span class="token punctuation">.</span><span class="token function">length</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">3</span><span class="token punctuation">)</span>
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||||
<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>
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<span class="token punctuation">}</span>
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||||
<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></div></div><h3 id="_1-2-stream流式思想概述"><a href="#_1-2-stream流式思想概述" class="header-anchor">#</a> 1.2 Stream流式思想概述</h3> <p><strong>注意：Stream和IO流(InputStream/OutputStream)没有任何关系，请暂时忘记对传统IO流的固有印象</strong>！</p> <p>Stream流式思想类似于工厂车间的“生产流水线”，Stream流不是一种数据结构，不保存数据，而是对数据进行加工处理。Stream可以看作是流水线上的一个工序。在流水线上，通过多个工序让一个原材料加工成一个商品。</p> <p><img src="/java8/Stream%E6%B5%81%E5%BC%8F%E6%80%9D%E6%83%B3.png" alt=""></p> <p><img src="/java8/Stream%E6%B5%81%E5%BC%8F%E6%80%9D%E6%83%B31.png" alt=""></p> <p>Stream API能让我们快速完成许多复杂的操作，如筛选、切片、映射、查找、去除重复，统计，匹配和归约。</p> <h3 id="_1-3-获取stream流的两种方式"><a href="#_1-3-获取stream流的两种方式" class="header-anchor">#</a> 1.3 获取Stream流的两种方式</h3> <ul><li>方式一
|
||||
<ul><li>Collection集合接口中有默认方法<code>default Stream<E> stream(){...}</code></li> <li>也就是说实现该接口的集合类都可以直接调用stream()方法获取流对象</li></ul></li> <li>方式二
|
||||
<ul><li>Stream中的静态方法<code>static<T> Stream<T> of(T t){...}</code></li> <li>可以调用该方法获取流对象</li></ul></li></ul> <h3 id="_1-4-了解stream流的常用方法和注意事项"><a href="#_1-4-了解stream流的常用方法和注意事项" class="header-anchor">#</a> 1.4 了解Stream流的常用方法和注意事项</h3> <ul><li>Stream常用方法</li></ul> <table><thead><tr><th>方法名</th> <th>方法作用</th> <th>返回值类型</th> <th>方法种类</th></tr></thead> <tbody><tr><td>count</td> <td>统计个数</td> <td>long</td> <td>终结</td></tr> <tr><td>forEach</td> <td>逐一处理</td> <td>void</td> <td>终结</td></tr> <tr><td>filter</td> <td>过滤</td> <td>Stream</td> <td>函数拼接</td></tr> <tr><td>limit</td> <td>取用前几个</td> <td>Stream</td> <td>函数拼接</td></tr> <tr><td>skip</td> <td>跳过前几个</td> <td>Stream</td> <td>函数拼接</td></tr> <tr><td>map</td> <td>映射</td> <td>Stream</td> <td>函数拼接</td></tr> <tr><td>concat</td> <td>组合</td> <td>Stream</td> <td>函数拼接</td></tr></tbody></table> <ul><li><p>终结方法：返回值类型不再是 Stream 类型的方法，不再支持链式调用。</p></li> <li><p>非终结方法：返回值类型仍然是 Stream 类型的方法，支持链式调用。（除了终结方法外，其余方法均为非终结方法。）</p></li> <li><p>Stream注意事项</p> <ol><li>Stream只能操作一次</li> <li>Stream方法返回的是新的流</li> <li>Stream不调用终结方法，中间的操作不会执行</li></ol></li></ul> <h4 id="foreach"><a href="#foreach" class="header-anchor">#</a> forEach</h4> <ul><li>forEach用来遍历流中的数据 -> 终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>void forEach(Consumer&lt;? super T> action);
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>该方法接收一个 Consumer 接口函数，会将每一个流元素交给该函数进行处理。</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">StreamTest</span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list<span class="token punctuation">;</span>
|
||||
|
||||
<span class="token annotation punctuation">@Before</span>
|
||||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">before</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</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">forEach</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list<span class="token punctuation">.</span><span class="token function">stream</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 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><h4 id="count"><a href="#count" class="header-anchor">#</a> count</h4> <ul><li>count方法来统计其中的元素个数 -> 终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>long count();
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>该方法返回一个long值代表元素个数。基本使用</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">StreamTest</span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list<span class="token punctuation">;</span>
|
||||
|
||||
<span class="token annotation punctuation">@Before</span>
|
||||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">before</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</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">count</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>list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">count</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></div></div><h4 id="filter"><a href="#filter" class="header-anchor">#</a> filter</h4> <ul><li>filter用于过滤数据，返回符合过滤条件的数据 -> 非终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>Stream&lt;T> filter(Predicate&lt;? super T> predicate);
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li><p><img src="/java8/filter.png" alt=""></p></li> <li><p>该接口接收一个 Predicate 函数式接口参数(可以是一个Lambda或方法引用)作为筛选条件。</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">StreamTest</span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list<span class="token punctuation">;</span>
|
||||
|
||||
<span class="token annotation punctuation">@Before</span>
|
||||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">before</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"迪丽热巴"</span><span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</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">filter</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token comment">// 计算名字长度为3的人数</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>list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>name <span class="token operator">-></span> name<span class="token punctuation">.</span><span class="token function">length</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">count</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></div></div><h4 id="limit"><a href="#limit" class="header-anchor">#</a> limit</h4> <ul><li>limit 方法可以对流进行截取，只取用前n个 -> 非终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>Stream&lt;T> limit(long maxSize);
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>参数是一个long型，如果集合当前长度大于参数则进行截取。否则不进行操作</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">StreamTest</span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list<span class="token punctuation">;</span>
|
||||
|
||||
<span class="token annotation punctuation">@Before</span>
|
||||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">before</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"迪丽热巴"</span><span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</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">limit</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">limit</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 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 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><h4 id="skip"><a href="#skip" class="header-anchor">#</a> skip</h4> <ul><li>如果希望跳过前几个元素，可以使用 skip 方法获取一个截取之后的新流 -> 非终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>Stream&lt;T> skip(long n);
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>如果流的当前长度大于n，则跳过前n个; 否则将会得到一个长度为0的空流。</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">StreamTest</span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list<span class="token punctuation">;</span>
|
||||
|
||||
<span class="token annotation punctuation">@Before</span>
|
||||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">before</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"迪丽热巴"</span><span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</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">skip</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">skip</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 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 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><h4 id="map"><a href="#map" class="header-anchor">#</a> map</h4> <ul><li>如果需要将流中的元素映射到另一个流中，可以使用 map 方法 -> 非终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>&lt;R> Stream&lt;R> map(Function&lt;? super T, ? extends R> mapper);
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>该接口需要一个 Function 函数式接口参数，可以将当前流中的T类型数据转换为另一种R类型的流</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">StreamTest</span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list<span class="token punctuation">;</span>
|
||||
|
||||
<span class="token annotation punctuation">@Before</span>
|
||||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">before</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"迪丽热巴"</span><span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</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>
|
||||
list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// 类型增强</span>
|
||||
<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span>name <span class="token operator">-></span> <span class="token string">"name: "</span> <span class="token operator">+</span> name<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 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><h4 id="sorted"><a href="#sorted" class="header-anchor">#</a> sorted</h4> <ul><li>如果需要将数据排序，可以使用 sorted 方法。 -> 非终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>Stream&lt;T> sorted(); // 根据元素的自然顺序排序
|
||||
Stream&lt;T> sorted(Comparator&lt;? super T> comparator); // 自定义比较器排序
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><ul><li>该方法可以有两种不同地排序实现</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">StreamTest</span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list<span class="token punctuation">;</span>
|
||||
|
||||
<span class="token annotation punctuation">@Before</span>
|
||||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">before</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"迪丽热巴"</span><span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</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">sorted</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// 默认自然序</span>
|
||||
<span class="token punctuation">.</span><span class="token function">sorted</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// 执行比较器进行排序</span>
|
||||
<span class="token punctuation">.</span><span class="token function">sorted</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">(</span>o1<span class="token punctuation">,</span> o2<span class="token punctuation">)</span> <span class="token operator">-></span> o1<span class="token punctuation">.</span><span class="token function">length</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> o2<span class="token punctuation">.</span><span class="token function">length</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 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 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><h4 id="distinct"><a href="#distinct" class="header-anchor">#</a> distinct</h4> <ul><li>如果需要去除重复数据，可以使用 distinct 方法 -> 非终结方法
|
||||
<ul><li>自定义类型是根据对象的 hashCode 和 equals 来去除重复元素的</li></ul></li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>Stream&lt;T> distinct();
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>基本使用</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">StreamTest</span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list<span class="token punctuation">;</span>
|
||||
|
||||
<span class="token annotation punctuation">@Before</span>
|
||||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">before</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"迪丽热巴"</span><span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</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">distinct</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"迪丽热巴"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"张无忌"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">distinct</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 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><h4 id="match"><a href="#match" class="header-anchor">#</a> match</h4> <ul><li>如果需要判断数据是否匹配指定的条件，可以使用 Match 相关方法 -> 终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>boolean anyMatch(Predicate&lt;? super T> predicate);
|
||||
boolean allMatch(Predicate&lt;? super T> predicate);
|
||||
boolean noneMatch(Predicate&lt;? super T> predicate);
|
||||
</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><ul><li>基本使用</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">StreamTest</span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list<span class="token punctuation">;</span>
|
||||
|
||||
<span class="token annotation punctuation">@Before</span>
|
||||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">before</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"迪丽热巴"</span><span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</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">match</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token comment">// allMatch 所有元素都需要满足</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>list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">allMatch</span><span class="token punctuation">(</span>name <span class="token operator">-></span> name<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span><span class="token string">"张"</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">// anyMatch 如果有元素满足即可</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>list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">anyMatch</span><span class="token punctuation">(</span>name <span class="token operator">-></span> name<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span><span class="token string">"张"</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">// noneMatch 所有元素都不满足</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>list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">noneMatch</span><span class="token punctuation">(</span>name <span class="token operator">-></span> name<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span><span class="token string">"男"</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></div></div><h4 id="find"><a href="#find" class="header-anchor">#</a> find</h4> <ul><li>如果需要找到某些数据，可以使用 find 相关方法 -> 终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>Optional&lt;T> findFirst();
|
||||
Optional&lt;T> findAny();
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><ul><li>基本使用</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">StreamTest</span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">private</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list<span class="token punctuation">;</span>
|
||||
|
||||
<span class="token annotation punctuation">@Before</span>
|
||||
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">before</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list<span class="token punctuation">,</span> <span class="token string">"迪丽热巴"</span><span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"周芷若"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"赵敏"</span><span class="token punctuation">,</span> <span class="token string">"张强"</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">find</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token comment">// 都是获取第一个元素</span>
|
||||
<span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> optional <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">findAny</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> optional1 <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">findFirst</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>optional<span class="token punctuation">.</span><span class="token function">get</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>optional1<span class="token punctuation">.</span><span class="token function">get</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><h4 id="max-min"><a href="#max-min" class="header-anchor">#</a> max && min</h4> <ul><li>如果需要获取最大和最小值，可以使用 max 和 min 方法 -> 终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>Optional&lt;T> max(Comparator&lt;? super T> comparator);
|
||||
Optional&lt;T> min(Comparator&lt;? super T> comparator);
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><ul><li>基本使用</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">StreamTest</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">min_max</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token comment">// 传入一个比较器, 排序完后获取最后一个</span>
|
||||
<span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> max <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">7</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">max</span><span class="token punctuation">(</span><span class="token punctuation">(</span>o1<span class="token punctuation">,</span> o2<span class="token punctuation">)</span> <span class="token operator">-></span> o1 <span class="token operator">-</span> o2<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>max<span class="token punctuation">.</span><span class="token function">get</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">// 传入一个比较器, 排序完后获取第一个</span>
|
||||
<span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> min <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">7</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">min</span><span class="token punctuation">(</span><span class="token punctuation">(</span>o1<span class="token punctuation">,</span> o2<span class="token punctuation">)</span> <span class="token operator">-></span> o1 <span class="token operator">-</span> o2<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>min<span class="token punctuation">.</span><span class="token function">get</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></div></div><h4 id="reduce"><a href="#reduce" class="header-anchor">#</a> reduce</h4> <ul><li>如果需要将所有数据归纳得到一个数据，可以使用 reduce 方法 -> 终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>T reduce(T identity, BinaryOperator&lt;T> accumulator);
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>基本使用</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">StreamTest</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">reduce</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token class-name">Integer</span> reduce <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">9</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// T identity: 默认值</span>
|
||||
<span class="token comment">// BinaryOperator<T> accumulator: 对数据的处理方式</span>
|
||||
<span class="token comment">// 获取最大值, 初始值为0</span>
|
||||
<span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token operator">::</span><span class="token function">max</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>reduce<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
|
||||
reduce <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">9</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// T identity: 默认值</span>
|
||||
<span class="token comment">// BinaryOperator<T> accumulator: 对数据的处理方式</span>
|
||||
<span class="token comment">// 获取加和结果, 初始值为0</span>
|
||||
<span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token operator">::</span><span class="token function">sum</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>reduce<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><p><img src="/java8/reduce%E6%89%A7%E8%A1%8C%E6%B5%81%E7%A8%8B.png" alt=""></p> <h4 id="map-reduce结合"><a href="#map-reduce结合" class="header-anchor">#</a> map && reduce结合</h4> <ul><li>使用案例</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">StreamTest</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">reduceAndMap</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token comment">// 获取最大年龄</span>
|
||||
<span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> maxAge <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"张三"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"李四"</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 keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"王五"</span><span class="token punctuation">,</span> <span class="token number">17</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小红"</span><span class="token punctuation">,</span> <span class="token number">19</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小明"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token operator">::</span><span class="token function">getAge</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">(</span><span class="token class-name">Integer</span><span class="token operator">::</span><span class="token function">max</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>maxAge<span class="token punctuation">.</span><span class="token function">get</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">// 获取年龄总和</span>
|
||||
<span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> totalAge <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"张三"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"李四"</span><span class="token punctuation">,</span> <span class="token number">22</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"王五"</span><span class="token punctuation">,</span> <span class="token number">17</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小红"</span><span class="token punctuation">,</span> <span class="token number">19</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小明"</span><span class="token punctuation">,</span> <span class="token number">21</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token operator">::</span><span class="token function">getAge</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">(</span><span class="token class-name">Integer</span><span class="token operator">::</span><span class="token function">sum</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>totalAge<span class="token punctuation">.</span><span class="token function">get</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><span class="line-number">26</span><br></div></div><h4 id="maptoint"><a href="#maptoint" class="header-anchor">#</a> mapToInt</h4> <ul><li>如果需要将Stream中的Integer类型数据转成int类型，可以使用 mapToInt 方法 -> 终结方法</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>IntStream mapToInt(ToIntFunction&lt;? super T> mapper);
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li><p><img src="/java8/filter.png" alt=""></p></li> <li><p>该接口需要一个 Function 函数式接口参数，可以将当前流中的T类型数据转换为另一种R类型的流</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">StreamTest</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">mapToInt</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token comment">// Integer占用的内存比int多, 在Stream流中会自动拆箱装箱</span>
|
||||
<span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> stream <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token comment">// 将Integer类型转换为int类型, 可以节省空间</span>
|
||||
<span class="token class-name">IntStream</span> intStream <span class="token operator">=</span> stream
|
||||
<span class="token punctuation">.</span><span class="token function">mapToInt</span><span class="token punctuation">(</span><span class="token class-name">Integer</span><span class="token operator">::</span><span class="token function">intValue</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></div></div><h4 id="concat"><a href="#concat" class="header-anchor">#</a> concat</h4> <ul><li>如果有两个流，希望合并成为一个流，那么可以使用 Stream 接口的静态方法 concat -> 终结方法
|
||||
<ul><li>这是一个静态方法，与 <code>java.lang.String</code> 当中的 concat 方法是不同的</li></ul></li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>static &lt;T> Stream&lt;T> concat(Stream&lt;? extends T> a, Stream&lt;? extends T> b){...}
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>基本使用</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">StreamTest</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">concat</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> streamA <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token string">"张三"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> streamB <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token string">"李四"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token comment">// 将以上流合并, 合并的流就不能够继续操作了</span>
|
||||
<span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span>streamA<span class="token punctuation">,</span> streamB<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 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></div></div><h3 id="_1-5-stream综合案例"><a href="#_1-5-stream综合案例" class="header-anchor">#</a> 1.5 Stream综合案例</h3> <ul><li>现在有两个 ArrayList 集合存储队伍当中的多个成员姓名，要求使用Stream实现若干操作步骤：
|
||||
<ol><li>第一个队伍只要名字为3个字的成员姓名；</li> <li>第一个队伍筛选之后只要前3个人；</li> <li>第二个队伍只要姓张的成员姓名；</li> <li>第二个队伍筛选之后不要前2个人；</li> <li>将两个队伍合并为一个队伍；</li> <li>根据姓名创建 Person 对象；</li> <li>打印整个队伍的Person对象信息。</li></ol></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">StreamCaseDemo</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 class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> one <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> two <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>one<span class="token punctuation">,</span> <span class="token string">"迪丽热巴"</span><span class="token punctuation">,</span> <span class="token string">"宋远桥"</span><span class="token punctuation">,</span> <span class="token string">"苏星河"</span><span class="token punctuation">,</span> <span class="token string">"老子"</span><span class="token punctuation">,</span> <span class="token string">"庄子"</span><span class="token punctuation">,</span> <span class="token string">"孙子"</span><span class="token punctuation">,</span> <span class="token string">"洪七公"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token class-name">Collections</span><span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>two<span class="token punctuation">,</span> <span class="token string">"古力娜扎"</span><span class="token punctuation">,</span> <span class="token string">"张无忌"</span><span class="token punctuation">,</span> <span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token string">"赵丽颖"</span><span class="token punctuation">,</span> <span class="token string">"张二狗"</span><span class="token punctuation">,</span> <span class="token string">"张天爱"</span><span class="token punctuation">,</span> <span class="token string">"张三"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
|
||||
<span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> streamOne <span class="token operator">=</span> one<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// 1. 第一个队伍只要名字为3个字的成员姓名</span>
|
||||
<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>name <span class="token operator">-></span> name<span class="token punctuation">.</span><span class="token function">length</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">3</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// 2. 第一个队伍筛选之后只要前3个人</span>
|
||||
<span class="token punctuation">.</span><span class="token function">limit</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 class-name">Stream</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> streamTwo <span class="token operator">=</span> two<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// 3. 第二个队伍只要姓张的成员姓名</span>
|
||||
<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>name <span class="token operator">-></span> name<span class="token punctuation">.</span><span class="token function">startsWith</span><span class="token punctuation">(</span><span class="token string">"张"</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// 4. 第二个队伍筛选之后不要前2个人</span>
|
||||
<span class="token punctuation">.</span><span class="token function">skip</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">// 5. 将两个队伍合并为一个队伍</span>
|
||||
<span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> stream <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span>streamOne<span class="token punctuation">,</span> streamTwo<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
<span class="token comment">// 6. 根据姓名创建 Person 对象</span>
|
||||
stream<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token operator">::</span><span class="token keyword">new</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// 7. 打印整个队伍的Person对象信息</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 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><h3 id="_1-6-收集stream流中的结果"><a href="#_1-6-收集stream流中的结果" class="header-anchor">#</a> 1.6 收集Stream流中的结果</h3> <ul><li>对流操作完成之后，如果需要将流的结果保存到数组或集合中，可以收集流中的数据</li></ul> <h4 id="收集结果到集合中"><a href="#收集结果到集合中" class="header-anchor">#</a> 收集结果到集合中</h4> <ul><li>Stream流提供 collect 方法，其参数需要一个<code>java.util.stream.Collector<T,A, R></code>接口对象来指定收集到哪种集合中。<code>java.util.stream.Collectors</code>类提供一些方法，可以作为Collector`接口的实例：
|
||||
<ul><li><code>public static <T> Collector<T, ?, List<T>> toList()</code>: 转换为 List 集合</li> <li><code>public static <T> Collector<T, ?, Set<T>> toSet()</code>: 转换为 Set 集合</li> <li><code>public static <T, C extends Collection<T>> Collector<T, ?, C> toCollection(Supplier<C> collectionFactory)</code>: 收集到指定的集合中</li></ul></li></ul> <h4 id="收集结果到数组中"><a href="#收集结果到数组中" class="header-anchor">#</a> 收集结果到数组中</h4> <ul><li>Stream提供 toArray 方法来将结果放到一个数组中</li></ul> <div class="language-text line-numbers-mode"><pre class="language-text"><code>Object[] toArray(); // 返回Object数组
|
||||
&lt;A> A[] toArray(IntFunction&lt;A[]> generator); // 返回指定数组
|
||||
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h4 id="对流中数据进行聚合计算"><a href="#对流中数据进行聚合计算" class="header-anchor">#</a> 对流中数据进行聚合计算</h4> <ul><li>当我们使用Stream流处理数据后，可以像数据库的聚合函数一样对某个字段进行操作。比如获取最大值，获取最小值，求总和，平均值，统计数量。</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">StreamCollectTest</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">aggregation</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Person</span><span class="token punctuation">></span></span> personList <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"张三"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"李四"</span><span class="token punctuation">,</span> <span class="token number">22</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"王五"</span><span class="token punctuation">,</span> <span class="token number">17</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小红"</span><span class="token punctuation">,</span> <span class="token number">19</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小明"</span><span class="token punctuation">,</span> <span class="token number">21</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">toList</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">// 获取最大值</span>
|
||||
<span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Person</span><span class="token punctuation">></span></span> optional <span class="token operator">=</span> personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">maxBy</span><span class="token punctuation">(</span><span class="token punctuation">(</span>o1<span class="token punctuation">,</span> o2<span class="token punctuation">)</span> <span class="token operator">-></span> o1<span class="token punctuation">.</span><span class="token function">getAge</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> o2<span class="token punctuation">.</span><span class="token function">getAge</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">"最大值: "</span> <span class="token operator">+</span> optional<span class="token punctuation">.</span><span class="token function">get</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">// 获取最小值</span>
|
||||
<span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Person</span><span class="token punctuation">></span></span> optionalMin <span class="token operator">=</span> personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">minBy</span><span class="token punctuation">(</span><span class="token punctuation">(</span>o1<span class="token punctuation">,</span> o2<span class="token punctuation">)</span> <span class="token operator">-></span> o1<span class="token punctuation">.</span><span class="token function">getAge</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> o2<span class="token punctuation">.</span><span class="token function">getAge</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">"最小值: "</span> <span class="token operator">+</span> optionalMin<span class="token punctuation">.</span><span class="token function">get</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">// 求总和</span>
|
||||
<span class="token class-name">Integer</span> totalAge <span class="token operator">=</span> personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">summingInt</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token operator">::</span><span class="token function">getAge</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">"总和: "</span> <span class="token operator">+</span> totalAge<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
|
||||
<span class="token comment">// 平均值</span>
|
||||
<span class="token class-name">Double</span> avg <span class="token operator">=</span> personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">averagingInt</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token operator">::</span><span class="token function">getAge</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">"平均值: "</span> <span class="token operator">+</span> avg<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
|
||||
<span class="token comment">// 统计数量</span>
|
||||
<span class="token class-name">Long</span> count <span class="token operator">=</span> personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">counting</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">"总共: "</span> <span class="token operator">+</span> count<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
|
||||
<span class="token comment">// 以上方法聚合</span>
|
||||
<span class="token class-name">IntSummaryStatistics</span> summaryStatistics <span class="token operator">=</span> personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">summarizingInt</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token operator">::</span><span class="token function">getAge</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">"上面所有方法的聚合: "</span> <span class="token operator">+</span> summaryStatistics<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></div></div><h4 id="对流中数据进行分组"><a href="#对流中数据进行分组" class="header-anchor">#</a> 对流中数据进行分组</h4> <ul><li>当我们使用Stream流处理数据后，可以根据某个属性将数据分组</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">StreamCollectTest</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">group</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Person</span><span class="token punctuation">></span></span> personList <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"张三"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"李四"</span><span class="token punctuation">,</span> <span class="token number">22</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"王五"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小红"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小明"</span><span class="token punctuation">,</span> <span class="token number">21</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">toList</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">// 通过年龄来进行分组</span>
|
||||
personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">groupingBy</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token operator">::</span><span class="token function">getAge</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// 分组结果为键值对</span>
|
||||
<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span>key<span class="token punctuation">,</span> value<span class="token punctuation">)</span> <span class="token operator">-></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>key <span class="token operator">+</span> <span class="token string">"::"</span> <span class="token operator">+</span> value<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
|
||||
<span class="token comment">// 将年龄大于19的分为一组, 小于19分为一组</span>
|
||||
personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">groupingBy</span><span class="token punctuation">(</span>s <span class="token operator">-></span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">if</span><span class="token punctuation">(</span>s<span class="token punctuation">.</span><span class="token function">getAge</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> <span class="token number">19</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token keyword">return</span> <span class="token string">">=19"</span><span class="token punctuation">;</span>
|
||||
<span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
|
||||
<span class="token keyword">return</span> <span class="token string">"<19"</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">// 分组结果为键值对, 键为groupingBy返回的数据</span>
|
||||
<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span>k<span class="token punctuation">,</span> v<span class="token punctuation">)</span> <span class="token operator">-></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>k <span class="token operator">+</span> <span class="token string">"::"</span> <span class="token operator">+</span> v<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><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></div></div><h4 id="对流中数据进行多级分组"><a href="#对流中数据进行多级分组" class="header-anchor">#</a> 对流中数据进行多级分组</h4> <ul><li>还可以对数据进行多级分组：</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">StreamCollectTest</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">multiGroup</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Person</span><span class="token punctuation">></span></span> personList <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"张三丰"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"迪丽热巴"</span><span class="token punctuation">,</span> <span class="token number">22</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"古力娜扎"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"迪迦奥特曼"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"宇宙无敌法外狂徒张三"</span><span class="token punctuation">,</span> <span class="token number">21</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">toList</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">// 先根据年龄分组, 每组中再根据名字的长度分组</span>
|
||||
personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span>
|
||||
<span class="token comment">// 根据年龄分组</span>
|
||||
<span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">groupingBy</span><span class="token punctuation">(</span>p <span class="token operator">-></span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">if</span><span class="token punctuation">(</span>p<span class="token punctuation">.</span><span class="token function">getAge</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> <span class="token number">19</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token keyword">return</span> <span class="token string">"大于19"</span><span class="token punctuation">;</span>
|
||||
<span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
|
||||
<span class="token keyword">return</span> <span class="token string">"小于等于19"</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">// 根据名字长度分组</span>
|
||||
<span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">groupingBy</span><span class="token punctuation">(</span>p <span class="token operator">-></span> <span class="token punctuation">{</span>
|
||||
<span class="token keyword">if</span><span class="token punctuation">(</span>p<span class="token punctuation">.</span><span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">length</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> <span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token keyword">return</span> <span class="token string">"较长的名字"</span><span class="token punctuation">;</span>
|
||||
<span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
|
||||
<span class="token keyword">return</span> <span class="token string">"较短的名字"</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">// 结果的类型为: Map<String, Map<String, Person>></span>
|
||||
<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span>oneK<span class="token punctuation">,</span> oneV<span class="token punctuation">)</span> <span class="token operator">-></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">"年龄"</span> <span class="token operator">+</span> oneK<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
oneV<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span>twoK<span class="token punctuation">,</span> twoV<span class="token punctuation">)</span> <span class="token operator">-></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">"\t"</span> <span class="token operator">+</span> twoK <span class="token operator">+</span> <span class="token string">"::"</span> <span class="token operator">+</span> twoV<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 comment">/*
|
||||
result -> {
|
||||
年龄小于等于19
|
||||
较长的名字::[Person{name='迪迦奥特曼', age=18}]
|
||||
较短的名字::[Person{name='张三丰', age=18}, Person{name='古力娜扎', age=18}]
|
||||
年龄大于19
|
||||
较长的名字::[Person{name='宇宙无敌法外狂徒张三', age=21}]
|
||||
较短的名字::[Person{name='迪丽热巴', age=22}]
|
||||
}
|
||||
*/</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><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br><span class="line-number">50</span><br></div></div><h4 id="对流中数据进行分区"><a href="#对流中数据进行分区" class="header-anchor">#</a> 对流中数据进行分区</h4> <ul><li><code>Collectors.partitioningBy</code>会根据值是否为true，把集合分割为两个列表，一个true列表，一个false列表</li> <li><img src="/java8/%E6%B5%81%E6%95%B0%E6%8D%AE%E5%88%86%E5%8C%BA.png" alt=""></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">StreamCollectTest</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">partition</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
|
||||
<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Person</span><span class="token punctuation">></span></span> personList <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"张三"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"李四"</span><span class="token punctuation">,</span> <span class="token number">22</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"王五"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小红"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小明"</span><span class="token punctuation">,</span> <span class="token number">21</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">toList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
|
||||
personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// 将结果分为, true和false两个分区</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">partitioningBy</span><span class="token punctuation">(</span>p <span class="token operator">-></span> p<span class="token punctuation">.</span><span class="token function">getAge</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> <span class="token number">19</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 punctuation">(</span>k<span class="token punctuation">,</span> v<span class="token punctuation">)</span> <span class="token operator">-></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>k <span class="token operator">+</span> <span class="token string">"::"</span> <span class="token operator">+</span> v<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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</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><h4 id="对流中数据进行拼接"><a href="#对流中数据进行拼接" class="header-anchor">#</a> 对流中数据进行拼接</h4> <ul><li><code>Collectors.joining</code>会根据指定的连接符，将所有元素连接成一个字符串</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">StreamCollectTest</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">join</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
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||||
<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Person</span><span class="token punctuation">></span></span> personList <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"张三"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"李四"</span><span class="token punctuation">,</span> <span class="token number">22</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"王五"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小红"</span><span class="token punctuation">,</span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
|
||||
<span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token string">"小明"</span><span class="token punctuation">,</span> <span class="token number">21</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">toList</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">// 根据一个字符拼接</span>
|
||||
<span class="token class-name">String</span> names <span class="token operator">=</span> personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token operator">::</span><span class="token function">getName</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">joining</span><span class="token punctuation">(</span><span class="token string">"-"</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>names<span class="token punctuation">)</span><span class="token punctuation">;</span>
|
||||
|
||||
<span class="token comment">// 根据三个字符拼接</span>
|
||||
names <span class="token operator">=</span> personList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||||
<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token operator">::</span><span class="token function">getName</span><span class="token punctuation">)</span>
|
||||
<span class="token comment">// 参数说明: 分隔符, 前缀, 后缀</span>
|
||||
<span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">joining</span><span class="token punctuation">(</span><span class="token string">","</span><span class="token punctuation">,</span> <span class="token string">"{"</span><span class="token punctuation">,</span> <span class="token string">"}"</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>names<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></div></section> <footer class="page-edit"><!----> <!----></footer> <div class="page-nav"><p class="inner"><span class="prev"><a href="/blogs/java/java8/java8-1.html" class="prev">
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JDK8 特性（一）
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JDK8 特性（三）
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</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/java8-2.html#_1-stream流" class="sidebar-link reco-side-_1-stream流" data-v-b57cc07c>1 Stream流</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-2.html#_1-1-集合处理数据的弊端" class="sidebar-link reco-side-_1-1-集合处理数据的弊端" data-v-b57cc07c>1.1 集合处理数据的弊端</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-2.html#_1-2-stream流式思想概述" class="sidebar-link reco-side-_1-2-stream流式思想概述" data-v-b57cc07c>1.2 Stream流式思想概述</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-2.html#_1-3-获取stream流的两种方式" class="sidebar-link reco-side-_1-3-获取stream流的两种方式" data-v-b57cc07c>1.3 获取Stream流的两种方式</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-2.html#_1-4-了解stream流的常用方法和注意事项" class="sidebar-link reco-side-_1-4-了解stream流的常用方法和注意事项" data-v-b57cc07c>1.4 了解Stream流的常用方法和注意事项</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-2.html#_1-5-stream综合案例" class="sidebar-link reco-side-_1-5-stream综合案例" data-v-b57cc07c>1.5 Stream综合案例</a></li><li class="level-3" data-v-b57cc07c><a href="/blogs/java/java8/java8-2.html#_1-6-收集stream流中的结果" class="sidebar-link reco-side-_1-6-收集stream流中的结果" data-v-b57cc07c>1.6 收集Stream流中的结果</a></li></ul></div></div></div><div class="global-ui"><div class="back-to-ceiling" style="right:1rem;bottom:6rem;width:2.5rem;height:2.5rem;border-radius:.25rem;line-height:2.5rem;display:none;" data-v-c6073ba8 data-v-c6073ba8><svg t="1574745035067" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="5404" class="icon" data-v-c6073ba8><path d="M526.60727968 10.90185116a27.675 27.675 0 0 0-29.21455937 0c-131.36607665 82.28402758-218.69155461 228.01873535-218.69155402 394.07834331a462.20625001 462.20625001 0 0 0 5.36959153 69.94390903c1.00431239 6.55289093-0.34802892 13.13561351-3.76865779 18.80351572-32.63518765 54.11355614-51.75690182 118.55860487-51.7569018 187.94566865a371.06718723 371.06718723 0 0 0 11.50484808 91.98906777c6.53300375 25.50556257 41.68394495 28.14064038 52.69160883 4.22606766 17.37162448-37.73630017 42.14135425-72.50938081 72.80769204-103.21549295 2.18761121 3.04276886 4.15646224 6.24463696 6.40373557 9.22774369a1871.4375 1871.4375 0 0 0 140.04691725 5.34970492 1866.36093723 1866.36093723 0 0 0 140.04691723-5.34970492c2.24727335-2.98310674 4.21612437-6.18497483 6.3937923-9.2178004 30.66633723 30.70611158 55.4360664 65.4791928 72.80769147 103.21549355 11.00766384 23.91457269 46.15860503 21.27949489 52.69160879-4.22606768a371.15156223 371.15156223 0 0 0 11.514792-91.99901164c0-69.36717486-19.13165746-133.82216804-51.75690182-187.92578088-3.42062944-5.66790279-4.76302748-12.26056868-3.76865837-18.80351632a462.20625001 462.20625001 0 0 0 5.36959269-69.943909c-0.00994388-166.08943902-87.32547796-311.81420293-218.6915546-394.09823051zM605.93803103 357.87693858a93.93749974 93.93749974 0 1 1-187.89594924 6.1e-7 93.93749974 93.93749974 0 0 1 187.89594924-6.1e-7z" p-id="5405" data-v-c6073ba8></path><path d="M429.50777625 765.63860547C429.50777625 803.39355007 466.44236686 1000.39046097 512.00932183 1000.39046097c45.56695499 0 82.4922232-197.00623328 82.5015456-234.7518555 0-37.75494459-36.9345906-68.35043303-82.4922232-68.34111062-45.57627738-0.00932239-82.52019037 30.59548842-82.51086798 68.34111062z" p-id="5406" data-v-c6073ba8></path></svg></div></div></div>
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