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<div id="app"><!--[--><!--[--><!--[--><span tabindex="-1"></span><a href="#main-content" class="skip-link sr-only">Skip to content</a><!--]--><div class="theme-container has-toc"><!--[--><!--[--><header class="navbar"><div class="navbar-left"><button class="toggle-sidebar-button" title="Toggle Sidebar"><span class="icon"></span></button><!----><a href="/" class="brand"><img class="logo" src="http://cdn.tobebetterjavaer.com/tobebetterjavaer/images/logo-02.png" alt="Java 程序员进阶之路"><!----><span class="site-name hide-in-pad">Java 程序员进阶之路</span></a><!----></div><div class="navbar-center"><!----><nav class="nav-links"><div class="nav-item hide-in-mobile"><a href="/blog.html" class="nav-link" aria-label="博客"><span class="icon iconfont icon-gaishu" style=""></span>博客<!----></a></div><div class="nav-item hide-in-mobile"><a href="/home.html" class="nav-link" aria-label="进阶之路"><span class="icon iconfont icon-lujing" style=""></span>进阶之路<!----></a></div><div class="nav-item hide-in-mobile"><a 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class="button-bottom"></span></span></button></div></header><!----><!--]--><!----><div class="toggle-sidebar-wrapper"><span class="arrow left"></span></div><aside class="sidebar"><!--[--><!----><!--]--><ul class="sidebar-links"><li><!--[--><a href="/home.html" class="nav-link sidebar-link sidebar-page" aria-label="一、前言"><!---->一、前言<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable active"><!----><span class="title">二、Java核心</span><span class="arrow down"></span></button><ul class="sidebar-links"><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.1 Java概述</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.2 Java语法基础</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.3 数组&字符串</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable active"><!----><span class="title">2.4 面向对象编程</span><span class="arrow down"></span></button><ul class="sidebar-links"><li><!--[--><a href="/oo/object-class.html" class="nav-link sidebar-link sidebar-page" aria-label="对象和类"><!---->对象和类<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/var.html" class="nav-link sidebar-link sidebar-page" aria-label="Java变量"><!---->Java变量<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/method.html" class="nav-link sidebar-link sidebar-page" aria-label="方法"><!---->方法<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/construct.html" class="nav-link sidebar-link sidebar-page" aria-label="构造方法"><!---->构造方法<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/nice-article/bokeyuan-jianxijavazhongdifangwenquanxiankongzhi.html" class="nav-link sidebar-link sidebar-page" aria-label="访问权限控制"><!---->访问权限控制<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a aria-current="page" href="/oo/code-init.html" class="router-link-active router-link-exact-active nav-link active sidebar-link sidebar-page active" aria-label="代码初始化块"><!---->代码初始化块<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/abstract.html" class="nav-link sidebar-link sidebar-page" aria-label="抽象类"><!---->抽象类<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/interface.html" class="nav-link sidebar-link sidebar-page" aria-label="接口"><!---->接口<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/inner-class.html" class="nav-link sidebar-link sidebar-page" aria-label="内部类"><!---->内部类<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/static.html" class="nav-link sidebar-link sidebar-page" aria-label="static"><!---->static<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/this-super.html" class="nav-link sidebar-link sidebar-page" aria-label="this 和 super"><!---->this 和 super<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/final.html" class="nav-link sidebar-link sidebar-page" aria-label="final"><!---->final<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/instanceof.html" class="nav-link sidebar-link sidebar-page" aria-label="instanceof"><!---->instanceof<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/immutable.html" class="nav-link sidebar-link sidebar-page" aria-label="不可变对象"><!---->不可变对象<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/varables.html" class="nav-link sidebar-link sidebar-page" aria-label="可变参数"><!---->可变参数<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/generic.html" class="nav-link sidebar-link sidebar-page" aria-label="泛型"><!---->泛型<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/annotation.html" class="nav-link sidebar-link sidebar-page" aria-label="注解"><!---->注解<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/enum.html" class="nav-link sidebar-link sidebar-page" aria-label="枚举"><!---->枚举<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/fanshe.html" class="nav-link sidebar-link sidebar-page" aria-label="反射"><!---->反射<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li></ul></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.5 集合框架（容器）</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.6 IO</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.7 异常处理</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.8 常用工具类</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.9 Java新特性</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.10 Java重要知识点</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.11 并发编程</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.12 JVM</span><span class="arrow right"></span></button><!----></section><!--]--></li></ul></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">三、Java企业级开发</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">四、数据库</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">五、计算机基础</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">六、求职面试</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">七、学习资源</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">八、学习建议</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">九、知识库搭建</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">十、联系作者</span><span class="arrow right"></span></button><!----></section><!--]--></li></ul><!--[--><!----><!--]--></aside><!--[--><main class="page" id="main-content"><!--[--><!----><nav class="breadcrumb disable"></nav><div class="page-title"><h1><!---->Java代码初始化块</h1><div class="page-info"><span class="author-info" aria-label="作者🖊" data-balloon-pos="down" isoriginal="false" pageview="false"><svg xmlns="http://www.w3.org/2000/svg" class="icon author-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="author icon"><path d="M649.6 633.6c86.4-48 147.2-144 147.2-249.6 0-160-128-288-288-288s-288 128-288 288c0 108.8 57.6 201.6 147.2 249.6-121.6 48-214.4 153.6-240 288-3.2 9.6 0 19.2 6.4 25.6 3.2 9.6 12.8 12.8 22.4 12.8h704c9.6 0 19.2-3.2 25.6-12.8 6.4-6.4 9.6-16 6.4-25.6-25.6-134.4-121.6-240-243.2-288z"></path></svg><span><a class="author-item" href="/about-the-author/" target="_blank" rel="noopener noreferrer">沉默王二</a></span><span property="author" content="沉默王二"></span></span><!----><span class="date-info" aria-label="写作日期📅" data-balloon-pos="down" isoriginal="false" pageview="false"><svg xmlns="http://www.w3.org/2000/svg" class="icon calendar-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="calendar icon"><path d="M716.4 110.137c0-18.753-14.72-33.473-33.472-33.473-18.753 0-33.473 14.72-33.473 33.473v33.473h66.993v-33.473zm-334.87 0c0-18.753-14.72-33.473-33.473-33.473s-33.52 14.72-33.52 33.473v33.473h66.993v-33.473zm468.81 33.52H716.4v100.465c0 18.753-14.72 33.473-33.472 33.473a33.145 33.145 0 01-33.473-33.473V143.657H381.53v100.465c0 18.753-14.72 33.473-33.473 33.473a33.145 33.145 0 01-33.473-33.473V143.657H180.6A134.314 134.314 0 0046.66 277.595v535.756A134.314 134.314 0 00180.6 947.289h669.74a134.36 134.36 0 00133.94-133.938V277.595a134.314 134.314 0 00-133.94-133.938zm33.473 267.877H147.126a33.145 33.145 0 01-33.473-33.473c0-18.752 14.72-33.473 33.473-33.473h736.687c18.752 0 33.472 14.72 33.472 33.473a33.145 33.145 0 01-33.472 33.473z"></path></svg><span>2021年10月22日</span><meta property="datePublished" content="2021-10-22T07:22:10.000Z"></span><span class="category-info" aria-label="分类🌈" data-balloon-pos="down" isoriginal="false" pageview="false"><svg xmlns="http://www.w3.org/2000/svg" class="icon category-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="category icon"><path d="M148.41 106.992h282.176c22.263 0 40.31 18.048 40.31 40.31V429.48c0 22.263-18.047 40.31-40.31 40.31H148.41c-22.263 0-40.311-18.047-40.311-40.31V147.302c0-22.263 18.048-40.31 40.311-40.31zM147.556 553.478H429.73c22.263 0 40.311 18.048 40.311 40.31v282.176c0 22.263-18.048 40.312-40.31 40.312H147.555c-22.263 0-40.311-18.049-40.311-40.312V593.79c0-22.263 18.048-40.311 40.31-40.311zM593.927 106.992h282.176c22.263 0 40.31 18.048 40.31 40.31V429.48c0 22.263-18.047 40.31-40.31 40.31H593.927c-22.263 0-40.311-18.047-40.311-40.31V147.302c0-22.263 18.048-40.31 40.31-40.31zM730.22 920.502H623.926c-40.925 0-74.22-33.388-74.22-74.425V623.992c0-41.038 33.387-74.424 74.425-74.424h222.085c41.038 0 74.424 33.226 74.424 74.067v114.233c0 10.244-8.304 18.548-18.547 18.548s-18.548-8.304-18.548-18.548V623.635c0-20.388-16.746-36.974-37.33-36.974H624.13c-20.585 0-37.331 16.747-37.331 37.33v222.086c0 20.585 16.654 37.331 37.126 37.331H730.22c10.243 0 18.547 8.304 18.547 18.547 0 10.244-8.304 18.547-18.547 18.547z"></path></svg><ul class="categories-wrapper"><li class="category category0 clickable" role="navigation">Java核心</li><meta property="articleSection" content="Java核心"></ul></span><span aria-label="标签🏷" data-balloon-pos="down" isoriginal="false" pageview="false"><svg xmlns="http://www.w3.org/2000/svg" class="icon tag-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="tag icon"><path d="M939.902 458.563L910.17 144.567c-1.507-16.272-14.465-29.13-30.737-30.737L565.438 84.098h-.402c-3.215 0-5.726 1.005-7.634 2.913l-470.39 470.39a10.004 10.004 0 000 14.164l365.423 365.424c1.909 1.908 4.42 2.913 7.132 2.913s5.223-1.005 7.132-2.913l470.39-470.39c2.01-2.11 3.014-5.023 2.813-8.036zm-240.067-72.121c-35.458 0-64.286-28.828-64.286-64.286s28.828-64.285 64.286-64.285 64.286 28.828 64.286 64.285-28.829 64.286-64.286 64.286z"></path></svg><ul class="tags-wrapper"><li class="tag tag4 clickable" role="navigation">Java</li></ul><meta property="keywords" content="Java"></span><span class="reading-time-info" aria-label="阅读时间⌛" data-balloon-pos="down" isoriginal="false" pageview="false"><svg xmlns="http://www.w3.org/2000/svg" class="icon timer-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="timer icon"><path d="M799.387 122.15c4.402-2.978 7.38-7.897 7.38-13.463v-1.165c0-8.933-7.38-16.312-16.312-16.312H256.33c-8.933 0-16.311 7.38-16.311 16.312v1.165c0 5.825 2.977 10.874 7.637 13.592 4.143 194.44 97.22 354.963 220.201 392.763-122.204 37.542-214.893 196.511-220.2 389.397-4.661 5.049-7.638 11.651-7.638 19.03v5.825h566.49v-5.825c0-7.379-2.849-13.981-7.509-18.9-5.049-193.016-97.867-351.985-220.2-389.527 123.24-37.67 216.446-198.453 220.588-392.892zM531.16 450.445v352.632c117.674 1.553 211.787 40.778 211.787 88.676H304.097c0-48.286 95.149-87.382 213.728-88.676V450.445c-93.077-3.107-167.901-81.297-167.901-177.093 0-8.803 6.99-15.793 15.793-15.793 8.803 0 15.794 6.99 15.794 15.793 0 80.261 63.69 145.635 142.01 145.635s142.011-65.374 142.011-145.635c0-8.803 6.99-15.793 15.794-15.793s15.793 6.99 15.793 15.793c0 95.019-73.789 172.82-165.96 177.093z"></path></svg><span>大约 3 分钟</span><meta property="timeRequired" content="PT3M"></span></div><hr></div><!----><!----><div class="theme-hope-content"><h1 id="java代码初始化块" tabindex="-1"><a class="header-anchor" href="#java代码初始化块" aria-hidden="true">#</a> Java代码初始化块</h1><p>“哥，今天我们要学习的内容是‘代码初始化块’，对吧？”看来三妹已经提前预习了我上次留给她的作业。</p><p>“是的，三妹。代码初始化块用于初始化一些成员变量。 ”我面带着朴实无华的微笑回答着她，“对象在创建的时候会执行代码初始化块。”</p><p>“可以直接通过‘=’操作符对成员变量进行初始化，但通过代码初始化块可以做更多的事情，比如说打印出成员变量初始化后的值。”</p><p>“三妹，来看下面的代码，我们可以直接通过 <code>=</code> 操作符对成员变量进行初始化。”</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">class</span> <span class="token class-name">Bike</span><span class="token punctuation">{</span>
<span class="token keyword">int</span> speed<span class="token operator">=</span><span class="token number">100</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>“哥，那为什么还需要代码初始化块呢？”三妹眨了眨眼睛，不解地问。</p><p>“我们可以通过代码初始化块执行一个更复杂的操作，比如为集合填充值。来看下面这段代码。”</p><div class="language-java ext-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">Bike</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> list<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>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"沉默王二"</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">"沉默王三"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token 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 keyword">new</span> <span class="token class-name">Bike</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 punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>“如果只使用‘=’操作符的话，是没办法完成集合初始化的，对吧？‘=’ 后面只能 new 出集合，却没办法填充值，代码初始化就可以完成这项工作。”</p><p>“构造方法执行得早还是代码初始化块啊，哥？”三妹这个问题问的还是挺有水平的。</p><p>“不要着急，三妹，先来看下面这个例子。”</p><div class="language-java ext-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">Car</span> <span class="token punctuation">{</span>
<span class="token class-name">Car</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">"构造方法"</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">"代码初始化块"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">new</span> <span class="token class-name">Car</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" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>“我们来看一下程序的输出结果就一下子明白了。”</p><div class="language-text ext-text line-numbers-mode"><pre class="language-text"><code>代码初始化块
构造方法
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div></div></div><p>“从输出结果看上去，仿佛代码初始化块执行得更早，对吧？事实上是这样子吗？”我露出神秘的微笑，问三妹。</p><p>“难道我看到的是假象吗？”三妹睁大了眼睛。</p><p>“不是的，对象在初始化的时候会先调用构造方法，这是毫无疑问的，只不过，构造方法在执行的时候会把代码初始化块放在构造方法中其他代码之前，所以，先看到了‘代码初始化块’，后看到了‘’构造方法’。”</p><p>说完这句话，我打开 draw.io，使上了吃奶的劲，画出了下面这幅图。</p><p><img src="http://cdn.tobebetterjavaer.com/tobebetterjavaer/images/object-class/22-01.png" alt=""></p><p>“哦，原来如此啊！”三妹仿佛发现了新大陆，意味深长地说。</p><p>等三妹明白彻底搞明白后，我对她继续说道：“对于代码初始化来说，它有三个规则。”</p><ul><li>类实例化的时候执行代码初始化块；</li><li>实际上，代码初始化块是放在构造方法中执行的，只不过比较靠前；</li><li>代码初始化块里的执行顺序是从前到后的。</li></ul><p>“这些规则不用死记硬背，大致了解一下就行了。我们继续来看下面这段代码。”话音刚落，我就在新版的 IDEA 中噼里啪啦地敲了起来，新版真香。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">class</span> <span class="token class-name">A</span> <span class="token punctuation">{</span>
<span class="token class-name">A</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">"父类构造方法"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">B</span> <span class="token keyword">extends</span> <span class="token class-name">A</span><span class="token punctuation">{</span>
<span class="token class-name">B</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">"子类构造方法"</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">"代码初始化块"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">new</span> <span class="token class-name">B</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" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>“来看一下输出结果。”</p><div class="language-text ext-text line-numbers-mode"><pre class="language-text"><code>父类构造方法
代码初始化块
子类构造方法
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>“在默认情况下，子类的构造方法在执行的时候会主动去调用父类的构造方法。也就是说，其实是构造方法先执行的，再执行的代码初始化块。”</p><p>“这个例子再次印证了之前的第二条规则：代码初始化块是放在构造方法中执行的，只不过比较靠前。”</p><p><img src="http://cdn.tobebetterjavaer.com/tobebetterjavaer/images/xingbiaogongzhonghao.png" alt=""></p></div><!----><footer class="page-meta"><div class="meta-item edit-link"><a href="https://github.com/itwanger/toBeBetterJavaer/edit/master/docs/oo/code-init.md" rel="noopener noreferrer" target="_blank" aria-label="在 GitHub 上编辑此页" class="nav-link label"><!--[--><svg xmlns="http://www.w3.org/2000/svg" class="icon edit-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="edit icon"><path d="M430.818 653.65a60.46 60.46 0 0 1-50.96-93.281l71.69-114.012 7.773-10.365L816.038 80.138A60.46 60.46 0 0 1 859.225 62a60.46 60.46 0 0 1 43.186 18.138l43.186 43.186a60.46 60.46 0 0 1 0 86.373L588.879 565.55l-8.637 8.637-117.466 68.234a60.46 60.46 0 0 1-31.958 11.229z"></path><path d="M728.802 962H252.891A190.883 190.883 0 0 1 62.008 771.98V296.934a190.883 190.883 0 0 1 190.883-192.61h267.754a60.46 60.46 0 0 1 0 120.92H252.891a69.962 69.962 0 0 0-69.098 69.099V771.98a69.962 69.962 0 0 0 69.098 69.098h475.911A69.962 69.962 0 0 0 797.9 771.98V503.363a60.46 60.46 0 1 1 120.922 0V771.98A190.883 190.883 0 0 1 728.802 962z"></path></svg><!--]-->在 GitHub 上编辑此页<span><svg class="external-link-icon" 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"><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="external-link-icon-sr-only">open in new window</span></span><!----></a></div><div class="meta-item update-time"><span class="label">上次编辑于: </span><span class="info">2022/5/14 上午7:14:28</span></div><div class="meta-item contributors"><span class="label">贡献者: </span><!--[--><!--[--><span class="contributor" title="email: [email protected]">itwanger</span>,<!--]--><!--[--><span class="contributor" title="email: [email protected]">沉默王二</span><!--]--><!--]--></div></footer><nav class="page-nav"><a href="/nice-article/bokeyuan-jianxijavazhongdifangwenquanxiankongzhi.html" class="nav-link prev" aria-label="访问权限控制"><div class="hint"><span class="arrow left"></span>上一页</div><div class="link"><!---->访问权限控制</div></a><a href="/oo/abstract.html" class="nav-link next" aria-label="抽象类"><div class="hint">下一页<span class="arrow right"></span></div><div class="link">抽象类<!----></div></a></nav><div class="giscus-wrapper input-top" style="display:block;">Loading...</div><!----><!--]--></main><!--]--><footer class="footer-wrapper"><div class="footer"><a href="https://beian.miit.gov.cn/" target="_blank">豫ICP备2021038026号-1</a><img src="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/beian.png" height="15px" width="15px" /><a target="_blank" href="http://www.beian.gov.cn/portal/registerSystemInfo?recordcode=41030502000411"><span>豫公网安备 41030502000411号</span></a></div><div class="copyright">Copyright © 2022 沉默王二</div></footer><!--]--></div><!--]--><!----><!----><!--]--></div>
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