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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 aria-current="page" href="/oo/construct.html" class="router-link-active router-link-exact-active nav-link active sidebar-link sidebar-page active" aria-label="构造方法"><!---->构造方法<!----></a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a aria-current="page" href="/oo/construct.html#_01、创建构造方法的规则有哪些" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="01、创建构造方法的规则有哪些"><!---->01、创建构造方法的规则有哪些<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/oo/construct.html#_02、-什么是默认构造方法" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="02、 什么是默认构造方法"><!---->02、 什么是默认构造方法<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/oo/construct.html#_03、什么是有参构造方法" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="03、什么是有参构造方法"><!---->03、什么是有参构造方法<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/oo/construct.html#_04、如何重载构造方法" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="04、如何重载构造方法"><!---->04、如何重载构造方法<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/oo/construct.html#_05、构造方法和方法有什么区别" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="05、构造方法和方法有什么区别"><!---->05、构造方法和方法有什么区别<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/oo/construct.html#_06、如何复制对象" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="06、如何复制对象"><!---->06、如何复制对象<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/oo/construct.html#_07、ending" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="07、ending"><!---->07、ending<!----></a><ul class="sidebar-sub-headers"></ul></li></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 href="/oo/code-init.html" class="nav-link sidebar-link sidebar-page" 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构造方法</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 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href="/oo/construct.html#_01、创建构造方法的规则有哪些" class="router-link-active router-link-exact-active toc-link level3">01、创建构造方法的规则有哪些</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/oo/construct.html#_02、-什么是默认构造方法" class="router-link-active router-link-exact-active toc-link level3">02、 什么是默认构造方法</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/oo/construct.html#_03、什么是有参构造方法" class="router-link-active router-link-exact-active toc-link level3">03、什么是有参构造方法</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/oo/construct.html#_04、如何重载构造方法" class="router-link-active router-link-exact-active toc-link level3">04、如何重载构造方法</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/oo/construct.html#_05、构造方法和方法有什么区别" class="router-link-active router-link-exact-active toc-link level3">05、构造方法和方法有什么区别</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/oo/construct.html#_06、如何复制对象" class="router-link-active router-link-exact-active toc-link level3">06、如何复制对象</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/oo/construct.html#_07、ending" class="router-link-active router-link-exact-active toc-link level3">07、ending</a></li><!----><!--]--></ul></div></aside></div><!----><div class="theme-hope-content"><h1 id="java构造方法" tabindex="-1"><a class="header-anchor" href="#java构造方法" aria-hidden="true">#</a> Java构造方法</h1><p>我对三妹说，“<a href="https://mp.weixin.qq.com/s/L4jAgQPurGZPvWu8ECtBpA" target="_blank" rel="noopener noreferrer">上一节<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>学了 Java 中的方法，接着学构造方法的话，难度就小很多了。”</p><p>“在 Java 中，构造方法是一种特殊的方法，当一个类被实例化的时候，就会调用构造方法。只有在构造方法被调用的时候，对象才会被分配内存空间。每次使用 <code>new</code> 关键字创建对象的时候，构造方法至少会被调用一次。”</p><p>“如果你在一个类中没有看见构造方法，并不是因为构造方法不存在，而是被缺省了，编译器会给这个类提供一个默认的构造方法。往大的方面说，就是，Java 有两种类型的构造方法：<strong>无参构造方法和有参构造方法</strong>。”</p><p>“注意，之所以叫它构造方法，是因为对象在创建的时候，需要通过构造方法初始化值——就是描写对象的那些状态，对应的是类中的字段。”</p><h3 id="_01、创建构造方法的规则有哪些" tabindex="-1"><a class="header-anchor" href="#_01、创建构造方法的规则有哪些" aria-hidden="true">#</a> 01、创建构造方法的规则有哪些</h3><p>构造方法必须符合以下规则：</p><ul><li>构造方法的名字必须和类名一样；</li><li>构造方法没有返回类型，包括 void；</li><li>构造方法不能是抽象的、静态的、最终的、同步的，也就是说，构造方法不能通过 abstract、static、final、synchronized 关键字修饰。</li></ul><p>简单解析一下最后一条规则。</p><ul><li>由于构造方法不能被子类继承，所以用 final 和 abstract 修饰没有意义；</li><li>构造方法用于初始化一个对象，所以用 static 修饰没有意义；</li><li>多个线程不会同时创建内存地址相同的同一个对象，所以用 synchronized 修饰没有必要。</li></ul><p>构造方法的语法格式如下：</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">class</span> class_name <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token function">class_name</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">// 默认无参构造方法</span>
<span class="token keyword">public</span> <span class="token function">ciass_name</span><span class="token punctuation">(</span><span class="token punctuation">[</span>paramList<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span> <span class="token comment">// 定义有参数列表的构造方法</span>
…
<span class="token comment">// 类主体</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></div><p>值得注意的是，如果用 void 声明构造方法的话，编译时不会报错，但 Java 会把这个所谓的“构造方法”当成普通方法来处理。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* 微信搜索「沉默王二」，回复 Java
*
* <span class="token keyword">@author</span> 沉默王二
* <span class="token keyword">@date</span> 2020/11/26
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Demo</span> <span class="token punctuation">{</span>
<span class="token keyword">void</span> <span class="token class-name">Demo</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></div><p><code>void Demo(){}</code> 看起来很符合构造方法的写法（与类名相同），但其实只是一个不符合规范的普通方法，方法名的首字母使用了大写，方法体为空，它并不是默认的无参构造方法，可以通过反编译后的字节码验证。</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">Demo</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token class-name">Demo</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">void</span> <span class="token class-name">Demo</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></div><p><code>public Demo() {}</code> 才是真正的无参构造方法。</p><p>不过，可以使用访问权限修饰符（private、protected、public、default）来修饰构造方法，访问权限修饰符决定了构造方法的创建方式。</p><h3 id="_02、-什么是默认构造方法" tabindex="-1"><a class="header-anchor" href="#_02、-什么是默认构造方法" aria-hidden="true">#</a> 02、 什么是默认构造方法</h3><p>如果一个构造方法中没有任何参数，那么它就是一个默认构造方法，也称为无参构造方法。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 微信搜「沉默王二」，回复关键字 PDF
*/</span>
<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">Bike</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">"一辆自行车被创建"</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">Bike</span> bike <span class="token operator">=</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>
<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></div><p>在上面这个例子中，我们为 Bike 类中创建了一个无参的构造方法，它在我们创建对象的时候被调用。</p><p>程序输出结果如下所示：</p><div class="language-text ext-text line-numbers-mode"><pre class="language-text"><code>一辆自行车被创建
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>通常情况下，无参构造方法是可以缺省的，我们开发者并不需要显式的声明无参构造方法，把这项工作交给编译器更轻松一些。</p><p><img src="http://cdn.tobebetterjavaer.com/tobebetterjavaer/images/object-class/18-01.png" alt=""></p><p>“二哥，默认构造方法的目的是什么？它为什么是一个空的啊？”三妹疑惑地看着我，提出了这个尖锐的问题。</p><p>“三妹啊，默认构造方法的目的主要是为对象的字段提供默认值，看下面这个例子你就明白了。”我胸有成竹地回答道。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 沉默王二，一枚有趣的程序员
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Person</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span> <span class="token class-name">String</span> name<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> age<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">Person</span> p <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Person</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">"姓名 "</span> <span class="token operator">+</span> p<span class="token punctuation">.</span>name <span class="token operator">+</span> <span class="token string">" 年龄 "</span> <span class="token operator">+</span> p<span class="token punctuation">.</span>age<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></div><p>输出结果如下所示：</p><div class="language-text ext-text line-numbers-mode"><pre class="language-text"><code>姓名 null 年龄 0
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>在上面的例子中，默认构造方法初始化了 name 和 age 的值，name 是 String 类型，所以默认值为 null，age 是 int 类型，所以默认值为 0。如果没有默认构造方法的话，这项工作就无法完成了。</p><h3 id="_03、什么是有参构造方法" tabindex="-1"><a class="header-anchor" href="#_03、什么是有参构造方法" aria-hidden="true">#</a> 03、什么是有参构造方法</h3><p>有参数的构造方法被称为有参构造方法，参数可以有一个或多个。有参构造方法可以为不同的对象提供不同的值。当然，也可以提供相同的值。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 沉默王二，一枚有趣的程序员
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">ParamConstructorPerson</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span> <span class="token class-name">String</span> name<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> age<span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token class-name">ParamConstructorPerson</span><span class="token punctuation">(</span><span class="token class-name">String</span> name<span class="token punctuation">,</span> <span class="token keyword">int</span> age<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>age <span class="token operator">=</span> age<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">out</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">"姓名 "</span> <span class="token operator">+</span> name <span class="token operator">+</span> <span class="token string">" 年龄 "</span> <span class="token operator">+</span> age<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">ParamConstructorPerson</span> p1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ParamConstructorPerson</span><span class="token punctuation">(</span><span class="token string">"沉默王二"</span><span class="token punctuation">,</span><span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
p1<span class="token punctuation">.</span><span class="token function">out</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">ParamConstructorPerson</span> p2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ParamConstructorPerson</span><span class="token punctuation">(</span><span class="token string">"沉默王三"</span><span class="token punctuation">,</span><span class="token number">16</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
p2<span class="token punctuation">.</span><span class="token function">out</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 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>在上面的例子中，构造方法有两个参数（name 和 age），这样的话，我们在创建对象的时候就可以直接为 name 和 age 赋值了。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">new</span> <span class="token class-name">ParamConstructorPerson</span><span class="token punctuation">(</span><span class="token string">"沉默王二"</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">ParamConstructorPerson</span><span class="token punctuation">(</span><span class="token string">"沉默王三"</span><span class="token punctuation">,</span><span class="token number">16</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></div><p>如果没有有参构造方法的话，就需要通过 setter 方法给字段赋值了。</p><h3 id="_04、如何重载构造方法" tabindex="-1"><a class="header-anchor" href="#_04、如何重载构造方法" aria-hidden="true">#</a> 04、如何重载构造方法</h3><p>在 Java 中，构造方法和方法类似，只不过没有返回类型。它也可以像方法一样被重载。构造方法的重载也很简单，只需要提供不同的参数列表即可。编译器会通过参数的数量来决定应该调用哪一个构造方法。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 沉默王二，一枚有趣的程序员
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">OverloadingConstrutorPerson</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span> <span class="token class-name">String</span> name<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> age<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> sex<span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token class-name">OverloadingConstrutorPerson</span><span class="token punctuation">(</span><span class="token class-name">String</span> name<span class="token punctuation">,</span> <span class="token keyword">int</span> age<span class="token punctuation">,</span> <span class="token keyword">int</span> sex<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>age <span class="token operator">=</span> age<span class="token punctuation">;</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>sex <span class="token operator">=</span> sex<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token class-name">OverloadingConstrutorPerson</span><span class="token punctuation">(</span><span class="token class-name">String</span> name<span class="token punctuation">,</span> <span class="token keyword">int</span> age<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>age <span class="token operator">=</span> age<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">out</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">"姓名 "</span> <span class="token operator">+</span> name <span class="token operator">+</span> <span class="token string">" 年龄 "</span> <span class="token operator">+</span> age <span class="token operator">+</span> <span class="token string">" 性别 "</span> <span class="token operator">+</span> sex<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">OverloadingConstrutorPerson</span> p1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">OverloadingConstrutorPerson</span><span class="token punctuation">(</span><span class="token string">"沉默王二"</span><span class="token punctuation">,</span><span class="token number">18</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
p1<span class="token punctuation">.</span><span class="token function">out</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">OverloadingConstrutorPerson</span> p2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">OverloadingConstrutorPerson</span><span class="token punctuation">(</span><span class="token string">"沉默王三"</span><span class="token punctuation">,</span><span class="token number">16</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
p2<span class="token punctuation">.</span><span class="token function">out</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 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>创建对象的时候，如果传递的是三个参数，那么就会调用 <code>OverloadingConstrutorPerson(String name, int age, int sex)</code> 这个构造方法；如果传递的是两个参数，那么就会调用 <code>OverloadingConstrutorPerson(String name, int age)</code> 这个构造方法。</p><h3 id="_05、构造方法和方法有什么区别" tabindex="-1"><a class="header-anchor" href="#_05、构造方法和方法有什么区别" aria-hidden="true">#</a> 05、构造方法和方法有什么区别</h3><p>构造方法和方法之间的区别还是蛮多的，比如说下面这些：</p><p><img src="http://cdn.tobebetterjavaer.com/tobebetterjavaer/images/object-class/18-02.png" alt=""></p><h3 id="_06、如何复制对象" tabindex="-1"><a class="header-anchor" href="#_06、如何复制对象" aria-hidden="true">#</a> 06、如何复制对象</h3><p>复制一个对象可以通过下面三种方式完成：</p><ul><li>通过构造方法</li><li>通过对象的值</li><li>通过 Object 类的 <code>clone()</code> 方法</li></ul><p>1）通过构造方法</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 沉默王二，一枚有趣的程序员
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">CopyConstrutorPerson</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span> <span class="token class-name">String</span> name<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> age<span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token class-name">CopyConstrutorPerson</span><span class="token punctuation">(</span><span class="token class-name">String</span> name<span class="token punctuation">,</span> <span class="token keyword">int</span> age<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>age <span class="token operator">=</span> age<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token class-name">CopyConstrutorPerson</span><span class="token punctuation">(</span><span class="token class-name">CopyConstrutorPerson</span> person<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> person<span class="token punctuation">.</span>name<span class="token punctuation">;</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>age <span class="token operator">=</span> person<span class="token punctuation">.</span>age<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">out</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">"姓名 "</span> <span class="token operator">+</span> name <span class="token operator">+</span> <span class="token string">" 年龄 "</span> <span class="token operator">+</span> age<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">CopyConstrutorPerson</span> p1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">CopyConstrutorPerson</span><span class="token punctuation">(</span><span class="token string">"沉默王二"</span><span class="token punctuation">,</span><span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
p1<span class="token punctuation">.</span><span class="token function">out</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">CopyConstrutorPerson</span> p2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">CopyConstrutorPerson</span><span class="token punctuation">(</span>p1<span class="token punctuation">)</span><span class="token punctuation">;</span>
p2<span class="token punctuation">.</span><span class="token function">out</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 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>在上面的例子中，有一个参数为 CopyConstrutorPerson 的构造方法，可以把该参数的字段直接复制到新的对象中，这样的话，就可以在 new 关键字创建新对象的时候把之前的 p1 对象传递过去。</p><p>2）通过对象的值</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 沉默王二，一枚有趣的程序员
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">CopyValuePerson</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span> <span class="token class-name">String</span> name<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> age<span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token class-name">CopyValuePerson</span><span class="token punctuation">(</span><span class="token class-name">String</span> name<span class="token punctuation">,</span> <span class="token keyword">int</span> age<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>age <span class="token operator">=</span> age<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token class-name">CopyValuePerson</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">void</span> <span class="token function">out</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">"姓名 "</span> <span class="token operator">+</span> name <span class="token operator">+</span> <span class="token string">" 年龄 "</span> <span class="token operator">+</span> age<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">CopyValuePerson</span> p1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">CopyValuePerson</span><span class="token punctuation">(</span><span class="token string">"沉默王二"</span><span class="token punctuation">,</span><span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
p1<span class="token punctuation">.</span><span class="token function">out</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">CopyValuePerson</span> p2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">CopyValuePerson</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
p2<span class="token punctuation">.</span>name <span class="token operator">=</span> p1<span class="token punctuation">.</span>name<span class="token punctuation">;</span>
p2<span class="token punctuation">.</span>age <span class="token operator">=</span> p1<span class="token punctuation">.</span>age<span class="token punctuation">;</span>
p2<span class="token punctuation">.</span><span class="token function">out</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 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>这种方式比较粗暴，直接拿 p1 的字段值复制给 p2 对象（<code>p2.name = p1.name</code>）。</p><p>3）通过 Object 类的 <code>clone()</code> 方法</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 沉默王二，一枚有趣的程序员
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">ClonePerson</span> <span class="token keyword">implements</span> <span class="token class-name">Cloneable</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span> <span class="token class-name">String</span> name<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> age<span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token class-name">ClonePerson</span><span class="token punctuation">(</span><span class="token class-name">String</span> name<span class="token punctuation">,</span> <span class="token keyword">int</span> age<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>age <span class="token operator">=</span> age<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token annotation punctuation">@Override</span>
<span class="token keyword">protected</span> <span class="token class-name">Object</span> <span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">CloneNotSupportedException</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> <span class="token keyword">super</span><span class="token punctuation">.</span><span class="token function">clone</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">void</span> <span class="token function">out</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">"姓名 "</span> <span class="token operator">+</span> name <span class="token operator">+</span> <span class="token string">" 年龄 "</span> <span class="token operator">+</span> age<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">CloneNotSupportedException</span> <span class="token punctuation">{</span>
<span class="token class-name">ClonePerson</span> p1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ClonePerson</span><span class="token punctuation">(</span><span class="token string">"沉默王二"</span><span class="token punctuation">,</span><span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
p1<span class="token punctuation">.</span><span class="token function">out</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">ClonePerson</span> p2 <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">ClonePerson</span><span class="token punctuation">)</span> p1<span class="token punctuation">.</span><span class="token function">clone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
p2<span class="token punctuation">.</span><span class="token function">out</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 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>通过 <code>clone()</code> 方法复制对象的时候，ClonePerson 必须先实现 Cloneable 接口的 <code>clone()</code> 方法，然后再调用 <code>clone()</code> 方法（<code>ClonePerson p2 = (ClonePerson) p1.clone()</code>）。</p><h3 id="_07、ending" tabindex="-1"><a class="header-anchor" href="#_07、ending" aria-hidden="true">#</a> 07、ending</h3><p>“二哥，我能问一些问题吗？”三妹精神焕发，没有丝毫的疲惫。</p><p>“当然可以啊，你问。”我很欣赏三妹孜孜不倦的态度。</p><p>“构造方法真的不返回任何值吗？”</p><p>“构造方法虽然没有返回值，但返回的是类的对象。”</p><p>“构造方法只能完成字段初始化的工作吗？”</p><p>“初始化字段只是构造方法的一种工作，它还可以做更多，比如启动线程，调用其他方法等。”</p><p>“好的，二哥，我的问题问完了，今天的学习可以结束了！”三妹一脸得意的样子。</p><p>“那你记得复习下一节的内容哦。”感受到三妹已经学到了知识，我也很欣慰。</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/construct.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="/oo/method.html" class="nav-link prev" aria-label="方法"><div class="hint"><span class="arrow left"></span>上一页</div><div class="link"><!---->方法</div></a><a href="/nice-article/bokeyuan-jianxijavazhongdifangwenquanxiankongzhi.html" class="nav-link next" aria-label="访问权限控制"><div class="hint">下一页<span class="arrow right"></span></div><div class="link">访问权限控制<!----></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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