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href="/basic-extra-meal/immutable.html#_04、总结" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="04、总结">04、总结</a><ul class="sidebar-sub-headers"></ul></li></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>深入理解Java中的不可变对象</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 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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 6 分钟</span><meta property="timeRequired" content="PT6M"></span></div><hr></div><div class="toc-place-holder"><aside id="toc"><div class="toc-header">此页内容</div><div class="toc-wrapper"><ul class="toc-list"><li class="toc-item"><a aria-current="page" href="/basic-extra-meal/immutable.html#_01、什么是不可变类" class="router-link-active router-link-exact-active toc-link level3">01、什么是不可变类</a></li><li class="toc-item"><a aria-current="page" href="/basic-extra-meal/immutable.html#_02、常见的不可变类" class="router-link-active router-link-exact-active toc-link level3">02、常见的不可变类</a></li><li class="toc-item"><a aria-current="page" href="/basic-extra-meal/immutable.html#_03、手撸不可变类" class="router-link-active router-link-exact-active toc-link level3">03、手撸不可变类</a></li><li class="toc-item"><a aria-current="page" href="/basic-extra-meal/immutable.html#_04、总结" class="router-link-active router-link-exact-active toc-link level3">04、总结</a></li></ul></div></aside></div><div class="theme-hope-content"><h1 id="深入理解java中的不可变对象" tabindex="-1"><a class="header-anchor" href="#深入理解java中的不可变对象" aria-hidden="true">#</a> 深入理解Java中的不可变对象</h1><blockquote><p>二哥，你能给我说说为什么 String 是 immutable 类（不可变对象）吗？我想研究它，想知道为什么它就不可变了，这种强烈的愿望就像想研究浩瀚的星空一样。但无奈自身功力有限，始终觉得雾里看花终隔一层。二哥你的文章总是充满趣味性，我想一定能够说明白，我也一定能够看明白，能在接下来写一写吗？</p></blockquote><p>收到读者小 R 的私信后，我就总感觉自己有一种义不容辞的责任，非要把 immutable 类说明白不可！</p><h3 id="_01、什么是不可变类" tabindex="-1"><a class="header-anchor" href="#_01、什么是不可变类" aria-hidden="true">#</a> 01、什么是不可变类</h3><p>一个类的对象在通过构造方法创建后如果状态不会再被改变，那么它就是一个不可变（immutable）类。它的所有成员变量的赋值仅在构造方法中完成，不会提供任何 setter 方法供外部类去修改。</p><p>还记得《神雕侠侣》中小龙女的古墓吗？随着那一声巨响，仅有的通道就被无情地关闭了。别较真那个密道，我这么说只是为了打开你的想象力，让你对不可变类有一个更直观的印象。</p><p>自从有了多线程，生产力就被无限地放大了，所有的程序员都爱它，因为强大的硬件能力被充分地利用了。但与此同时，所有的程序员都对它心生忌惮，因为一不小心，多线程就会把对象的状态变得混乱不堪。</p><p>为了保护状态的原子性、可见性、有序性，我们程序员可以说是竭尽所能。其中，synchronized（同步）关键字是最简单最入门的一种解决方案。</p><p>假如说类是不可变的，那么对象的状态就也是不可变的。这样的话，每次修改对象的状态，就会产生一个新的对象供不同的线程使用，我们程序员就不必再担心并发问题了。</p><h3 id="_02、常见的不可变类" tabindex="-1"><a class="header-anchor" href="#_02、常见的不可变类" aria-hidden="true">#</a> 02、常见的不可变类</h3><p>提到不可变类，几乎所有的程序员第一个想到的，就是 String 类。那为什么 String 类要被设计成不可变的呢？</p><p>1）常量池的需要</p><p>字符串常量池是 Java 堆内存中一个特殊的存储区域，当创建一个 String 对象时，假如此字符串在常量池中不存在，那么就创建一个；假如已经存，就不会再创建了，而是直接引用已经存在的对象。这样做能够减少 JVM 的内存开销，提高效率。</p><p>2）hashCode 的需要</p><p>因为字符串是不可变的，所以在它创建的时候，其 hashCode 就被缓存了，因此非常适合作为哈希值（比如说作为 HashMap 的键），多次调用只返回同一个值，来提高效率。</p><p>3）线程安全</p><p>就像之前说的那样，如果对象的状态是可变的，那么在多线程环境下，就很容易造成不可预期的结果。而 String 是不可变的，就可以在多个线程之间共享，不需要同步处理。</p><p>因此，当我们调用 String 类的任何方法（比如说 <code>trim()</code>、<code>substring()</code>、<code>toLowerCase()</code>）时，总会返回一个新的对象，而不影响之前的值。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token class-name">String</span> cmower <span class="token operator">=</span> <span class="token string">"沉默王二，一枚有趣的程序员"</span><span class="token punctuation">;</span>

cmower<span class="token punctuation">.</span><span class="token function">substring</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span><span class="token number">4</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>虽然调用 <code>substring()</code> 方法对 cmower 进行了截取，但 cmower 的值没有改变。</p><p>除了 String 类，包装器类 Integer、Long 等也是不可变类。</p><h3 id="_03、手撸不可变类" tabindex="-1"><a class="header-anchor" href="#_03、手撸不可变类" aria-hidden="true">#</a> 03、手撸不可变类</h3><p>看懂一个不可变类也许容易，但要创建一个自定义的不可变类恐怕就有点难了。但知难而进是我们作为一名优秀的程序员不可或缺的品质，正因为不容易，我们才能真正地掌握它。</p><p>接下来，就请和我一起，来自定义一个不可变类吧。一个不可变类，必须要满足以下 4 个条件：</p><p>1）确保类是 final 的，不允许被其他类继承。</p><p>2）确保所有的成员变量（字段）是 final 的，这样的话，它们就只能在构造方法中初始化值，并且不会在随后被修改。</p><p>3）不要提供任何 setter 方法。</p><p>4）如果要修改类的状态，必须返回一个新的对象。</p><p>按照以上条件，我们来自定义一个简单的不可变类 Writer。</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">final</span> <span class="token keyword">class</span> <span class="token class-name">Writer</span> <span class="token punctuation">{</span>

<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">String</span> name<span class="token punctuation">;</span>

<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">int</span> age<span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token class-name">Writer</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">public</span> <span class="token keyword">int</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 keyword">return</span> age<span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token class-name">String</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 keyword">return</span> name<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></div><p>Writer 类是 final 的，name 和 age 也是 final 的，没有 setter 方法。</p><p>OK，据说这个作者分享了很多博客，广受读者的喜爱，因此某某出版社找他写了一本书（Book）。Book 类是这样定义的：</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">Book</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> price<span class="token punctuation">;</span>

<span class="token keyword">return</span> name<span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">setName</span><span class="token punctuation">(</span><span class="token class-name">String</span> name<span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">getPrice</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">return</span> price<span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">setPrice</span><span class="token punctuation">(</span><span class="token keyword">int</span> price<span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">this</span><span class="token punctuation">.</span>price <span class="token operator">=</span> price<span class="token punctuation">;</span>

<span class="token annotation punctuation">@Override</span>

<span class="token keyword">public</span> <span class="token class-name">String</span> <span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">return</span> <span class="token string">"Book{"</span> <span class="token operator">+</span>

<span class="token string">", price="</span> <span class="token operator">+</span> price <span class="token operator">+</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></div><p>2 个字段，分别是 name 和 price，以及 getter 和 setter，重写后的 <code>toString()</code> 方法。然后，在 Writer 类中追加一个可变对象字段 book。</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">final</span> <span class="token keyword">class</span> <span class="token class-name">Writer</span> <span class="token punctuation">{</span>

<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">String</span> name<span class="token punctuation">;</span>

<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">int</span> age<span class="token punctuation">;</span>

<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name">Book</span> book<span class="token punctuation">;</span>

<span class="token keyword">return</span> age<span class="token punctuation">;</span>

<span class="token keyword">return</span> name<span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token class-name">Book</span> <span class="token function">getBook</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">return</span> book<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></div><p>并在构造方法中追加了 Book 参数，以及 Book 的 getter 方法。</p><p>完成以上工作后，我们来新建一个测试类，看看 Writer 类的状态是否真的不可变。</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">WriterDemo</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>

book<span class="token punctuation">.</span><span class="token function">setName</span><span class="token punctuation">(</span><span class="token string">"Web全栈开发进阶之路"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

book<span class="token punctuation">.</span><span class="token function">setPrice</span><span class="token punctuation">(</span><span class="token number">79</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token class-name">Writer</span> writer <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Writer</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> book<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">"定价："</span> <span class="token operator">+</span> writer<span class="token punctuation">.</span><span class="token function">getBook</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

writer<span class="token punctuation">.</span><span class="token function">getBook</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">setPrice</span><span class="token punctuation">(</span><span class="token number">59</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">"促销价："</span> <span class="token operator">+</span> writer<span class="token punctuation">.</span><span class="token function">getBook</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

促销价：<span class="token class-name">Book</span><span class="token punctuation">{</span>name<span class="token operator">=</span>'<span class="token class-name">Web</span>全栈开发进阶之路'<span class="token punctuation">,</span> price<span class="token operator">=</span><span class="token number">59</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>糟糕，Writer 类的不可变性被破坏了，价格发生了变化。为了解决这个问题，我们需要为不可变类的定义规则追加一条内容：</p><p>如果一个不可变类中包含了可变类的对象，那么就需要确保返回的是可变对象的副本。也就是说，Writer 类中的 <code>getBook()</code> 方法应该修改为：</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token class-name">Book</span> <span class="token function">getBook</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token class-name">Book</span> clone <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Book</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

clone<span class="token punctuation">.</span><span class="token function">setPrice</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span>book<span class="token punctuation">.</span><span class="token function">getPrice</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

clone<span class="token punctuation">.</span><span class="token function">setName</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span>book<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 punctuation">;</span>

<span class="token keyword">return</span> clone<span class="token punctuation">;</span>

促销价：Book{name='Web全栈开发进阶之路', price=79}

</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div></div></div><h3 id="_04、总结" tabindex="-1"><a class="header-anchor" href="#_04、总结" aria-hidden="true">#</a> 04、总结</h3><p>不可变类有很多优点，就像之前提到的 String 类那样，尤其是在多线程环境下，它非常的安全。尽管每次修改都会创建一个新的对象，增加了内存的消耗，但这个缺点相比它带来的优点，显然是微不足道的——无非就是捡了西瓜，丢了芝麻。</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/basic-extra-meal/immutable.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">2022/6/6 下午11:31:27</span></div><div class="meta-item contributors"><span class="label">贡献者: </span><span class="contributor" title="email: [email protected]">itwanger</span></div></footer><nav class="page-nav"><a href="/oo/instanceof.html" class="nav-link prev" aria-label="instanceof"><div class="hint"><span class="arrow left"></span>上一页</div><div class="link">instanceof</div></a><a href="/basic-extra-meal/varables.html" class="nav-link next" aria-label="可变参数"><div class="hint">下一页<span class="arrow right"></span></div><div class="link">可变参数</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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