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99.2-25.6 0 0 6.4-12.8 9.6-19.2 54.4-105.6 275.2-524.8 288-553.6 6.4-19.2-3.2-32-19.2-32C777.6 76.8 771.2 80 764.8 86.4z"></path></svg><div class="outlook-dropdown"><!----></div></button></div><div id="docsearch-container"></div><!--[--><!----><!--]--><button class="toggle-navbar-button" aria-label="Toggle Navbar" aria-expanded="false" aria-controls="nav-screen"><span class="button-container"><span class="button-top"></span><span class="button-middle"></span><span class="button-bottom"></span></span></button></div></header><!----><!--]--><!----><div class="toggle-sidebar-wrapper"><span class="arrow start"></span></div><aside class="sidebar" id="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基础</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概述及环境配置</span><span class="arrow end"></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 end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable active"><!----><span class="title">2.3 数组&字符串</span><span class="arrow down"></span></button><ul class="sidebar-links"><li><!--[--><a aria-current="page" href="/array/array.html" class="router-link-active router-link-exact-active nav-link active sidebar-link sidebar-page active" aria-label="掌握Java数组"><!---->掌握Java数组<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/array/double-array.html" class="nav-link sidebar-link sidebar-page" aria-label="掌握Java二维数组"><!---->掌握Java二维数组<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/array/print.html" class="nav-link sidebar-link sidebar-page" aria-label="打印Java数组"><!---->打印Java数组<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/string/string-source.html" class="nav-link sidebar-link sidebar-page" aria-label="解读String类源码"><!---->解读String类源码<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/string/immutable.html" class="nav-link sidebar-link sidebar-page" aria-label="String为什么不可变"><!---->String为什么不可变<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/string/constant-pool.html" class="nav-link sidebar-link sidebar-page" aria-label="深入理解Java字符串常量池"><!---->深入理解Java字符串常量池<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/string/intern.html" class="nav-link sidebar-link sidebar-page" aria-label="详解 String.intern 方法"><!---->详解 String.intern 方法<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/string/builder-buffer.html" class="nav-link sidebar-link sidebar-page" aria-label="StringBuilder和StringBuffer"><!---->StringBuilder和StringBuffer<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/string/equals.html" class="nav-link sidebar-link sidebar-page" aria-label="String相等判断"><!---->String相等判断<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/string/join.html" class="nav-link sidebar-link sidebar-page" aria-label="String拼接"><!---->String拼接<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/string/split.html" class="nav-link sidebar-link sidebar-page" aria-label="String拆分"><!---->String拆分<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li></ul></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.4 面向对象编程</span><span class="arrow end"></span></button><!----></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 end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.6 Java IO</span><span class="arrow end"></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 end"></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 end"></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 end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.10 网络编程</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.11 NIO</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.12 Java重要知识点</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.13 并发编程</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.14 JVM</span><span class="arrow end"></span></button><!----></section></li></ul></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">三、Java进阶</span><span class="arrow end"></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 end"></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 end"></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 end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">七、学习建议</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">八、知识库搭建</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">九、联系作者</span><span class="arrow end"></span></button><!----></section></li></ul><!--[--><!----><!--]--></aside><!--[--><main class="page" id="main-content"><!--[--><!----><nav class="breadcrumb disable"></nav><div class="page-title"><h1><!---->掌握Java数组：一个非常特殊的对象</h1><div class="page-info"><span class="page-author-info" aria-label="作者🖊" data-balloon-pos="down"><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="page-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="page-date-info" aria-label="写作日期📅" data-balloon-pos="down"><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><!----></span><meta property="datePublished" content="2021-10-22T07:22:10.000Z"></span><span class="page-category-info" aria-label="分类🌈" data-balloon-pos="down"><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><span class="page-category-item category0 clickable" role="navigation">Java核心</span><meta property="articleSection" content="Java核心"></span><span class="page-tag-info" aria-label="标签🏷" data-balloon-pos="down"><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><span class="page-tag-item tag5 clickable" role="navigation">数组&字符串</span><meta property="keywords" content="数组&字符串"></span><span class="page-word-info" aria-label="字数🔠" data-balloon-pos="down"><svg xmlns="http://www.w3.org/2000/svg" class="icon word-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="word icon"><path d="M518.217 432.64V73.143A73.143 73.143 0 01603.43 1.097a512 512 0 01419.474 419.474 73.143 73.143 0 01-72.046 85.212H591.36a73.143 73.143 0 01-73.143-73.143z"></path><path d="M493.714 566.857h340.297a73.143 73.143 0 0173.143 85.577A457.143 457.143 0 11371.566 117.76a73.143 73.143 0 0185.577 73.143v339.383a36.571 36.571 0 0036.571 36.571z"></path></svg><span>约 2412 字</span><meta property="wordCount" content="2412"></span><span class="page-reading-time-info" aria-label="阅读时间⌛" data-balloon-pos="down"><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 8 分钟</span><meta property="timeRequired" content="PT8M"></span></div><hr></div><!----><!----><div class="theme-hope-content"><h1 id="_4-1-掌握java数组" tabindex="-1"><a class="header-anchor" href="#_4-1-掌握java数组" aria-hidden="true">#</a> 4.1 掌握Java数组</h1><p>“二哥，我看你公众号的一篇文章里提到，<a href="https://tobebetterjavaer.com/collection/arraylist.html" target="_blank" rel="noopener noreferrer">ArrayList<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> 的内部是用数组实现的，我就对数组非常感兴趣，想深入地了解一下，今天终于到这个环节了，好期待呀！”三妹的语气里显得很兴奋。</p><p>“的确是的，看 ArrayList 的源码就一清二楚了。”我一边说，一边打开 Intellij IDEA，并找到了 ArrayList 的源码。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token doc-comment comment">/**
* The array buffer into which the elements of the ArrayList are stored.
* The capacity of the ArrayList is the length of this array buffer. Any
* empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
* will be expanded to DEFAULT_CAPACITY when the first element is added.
*/</span>
<span class="token keyword">transient</span> <span class="token class-name">Object</span><span class="token punctuation">[</span><span class="token punctuation">]</span> elementData<span class="token punctuation">;</span> <span class="token comment">// non-private to simplify nested class access</span>
<span class="token doc-comment comment">/**
* The size of the ArrayList (the number of elements it contains).
*
* <span class="token keyword">@serial</span>
*/</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> size<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></div><p>“瞧见没？<code>Object[] elementData</code> 就是数组。”我指着显示屏上这串代码继续说。</p><p>数组是一个对象，它包含了一组固定数量的元素，并且这些元素的类型是相同的。数组会按照索引的方式将元素放在指定的位置上，意味着我们可以通过索引来访问这些元素。在 Java 中，索引是从 0 开始的。</p><p>“哥，能说一下为什么索引从 0 开始吗？”三妹突然这个话题很感兴趣。</p><p>“哦，Java 是基于 C/C++ 语言实现的，而 C 语言的下标是从 0 开始的，所以 Java 就继承了这个良好的传统习惯。C语言有一个很重要概念，叫做指针，它实际上是一个偏移量，距离开始位置的偏移量，第一个元素就在开始的位置，它的偏移量就为 0，所以索引就为 0。”此刻，我很自信。</p><p>“此外，还有另外一种说法。早期的计算机资源比较匮乏，0 作为起始下标相比较于 1 作为起始下标，编译的效率更高。”</p><p>“哦。”三妹意味深长地点了点头。</p><p>我们可以将数组理解为一个个整齐排列的单元格，每个单元格里面存放着一个元素。</p><p>数组元素的类型可以是基本数据类型（比如说 int、double），也可以是引用数据类型（比如说 String），包括自定义类型。</p><p>数组的声明方式分两种。</p><p>先来看第一种：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> anArray<span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>再来看第二种：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">int</span> anOtherArray<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></div><p>不同之处就在于中括号的位置，是跟在类型关键字的后面，还是跟在变量的名称的后面。前一种的使用频率更高一些，像 ArrayList 的源码中就用了第一种方式。</p><p>同样的，数组的初始化方式也有多种，最常见的是：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> anArray <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">int</span><span class="token punctuation">[</span><span class="token number">10</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></div><p>看到了没？上面这行代码中使用了 new 关键字，这就意味着数组的确是一个对象，只有对象的创建才会用到 new 关键字，<a href="https://tobebetterjavaer.com/basic-grammar/basic-data-type.html" target="_blank" rel="noopener noreferrer">基本数据类型<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>是不用的。然后，我们需要在方括号中指定数组的长度。</p><p>这时候，数组中的每个元素都会被初始化为默认值，int 类型的就为 0，Object 类型的就为 null。 不同数据类型的默认值不同，可以参照<a href="https://tobebetterjavaer.com/basic-grammar/basic-data-type.html" target="_blank" rel="noopener noreferrer">之前的文章<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>。</p><p>另外，还可以使用大括号的方式，直接初始化数组中的元素：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">int</span> anOtherArray<span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token punctuation">{</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</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></div><p>这时候，数组的元素分别是 1、2、3、4、5，索引依次是 0、1、2、3、4，长度是 5。</p><p>“哥，怎么访问数组呢？”三妹及时地插话到。</p><p>前面提到过，可以通过索引来访问数组的元素，就像下面这样：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code>anArray<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token number">10</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>变量名，加上中括号，加上元素的索引，就可以访问到数组，通过“=”操作符可以对元素进行赋值。</p><p>如果索引的值超出了数组的界限，就会抛出 <code>ArrayIndexOutOfBoundException</code>。</p><p>既然数组的索引是从 0 开始，那就是到数组的 <code>length - 1</code> 结束，不要使用超出这个范围内的索引访问数组，就不会抛出数组越界的异常了。</p><p>当数组的元素非常多的时候，逐个访问数组就太辛苦了，所以需要通过遍历的方式。</p><p>第一种，使用 for 循环：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">int</span> anOtherArray<span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token punctuation">{</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> anOtherArray<span class="token punctuation">.</span>length<span class="token punctuation">;</span> i<span class="token operator">++</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>anOtherArray<span class="token punctuation">[</span>i<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></div><p>通过 length 属性获取到数组的长度，然后从 0 开始遍历，就得到了数组的所有元素。</p><p>第二种，使用 for-each 循环：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> element <span class="token operator">:</span> anOtherArray<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>element<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></div><p>如果不需要关心索引的话（意味着不需要修改数组的某个元素），使用 for-each 遍历更简洁一些。当然，也可以使用 while 和 do-while 循环。</p><p>在 Java 中，可变参数用于将任意数量的参数传递给方法，来看 <code>varargsMethod()</code> 方法：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">void</span> <span class="token function">varargsMethod</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span> varargs<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></div><p>该方法可以接收任意数量的字符串参数，可以是 0 个或者 N 个，本质上，可变参数就是通过数组实现的。为了证明这一点，我们可以看一下反编译一后的字节码：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">VarargsDemo</span>
<span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token class-name">VarargsDemo</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">transient</span> <span class="token keyword">void</span> <span class="token function">varargsMethod</span><span class="token punctuation">(</span><span class="token class-name">String</span> as<span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" 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></div><p>所以，我们其实可以直接将数组作为参数传递给该方法：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">VarargsDemo</span> demo <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">VarargsDemo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> anArray <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token punctuation">{</span><span class="token string">"沉默王二"</span><span class="token punctuation">,</span> <span class="token string">"一枚有趣的程序员"</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
demo<span class="token punctuation">.</span><span class="token function">varargsMethod</span><span class="token punctuation">(</span>anArray<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>也可以直接传递多个字符串，通过逗号隔开的方式：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code>demo<span class="token punctuation">.</span><span class="token function">varargsMethod</span><span class="token punctuation">(</span><span class="token string">"沉默王二"</span><span class="token punctuation">,</span> <span class="token string">"一枚有趣的程序员"</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></div><p>在 Java 中，数组与 List 关系非常密切。List 封装了很多常用的方法，方便我们对集合进行一些操作，而如果直接操作数组的话，有很多不便，因为数组本身没有提供这些封装好的操作，所以有时候我们需要把数组转成 List。</p><p>“怎么转呢？”三妹问到。</p><p>最原始的方式，就是通过遍历数组的方式，一个个将数组添加到 List 中。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> anArray <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token punctuation">{</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> aList <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> element <span class="token operator">:</span> anArray<span class="token punctuation">)</span> <span class="token punctuation">{</span>
aList<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span>element<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></div><p>更优雅的方式是通过 Arrays 类的 <code>asList()</code> 方法：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> aList <span class="token operator">=</span> <span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">asList</span><span class="token punctuation">(</span>anArray<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></div><p>不过需要注意的是，Arrays.asList 的参数需要是 Integer 数组，而 anArray 目前是 int 类型，我们需要换另外一种方式。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">List</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> aList <span class="token operator">=</span> <span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span>anArray<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">boxed</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">toList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>这又涉及到了 Java <a href="https://tobebetterjavaer.com/java8/stream.html" target="_blank" rel="noopener noreferrer">流<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>的知识，后面会讲到。</p><p>还有一个需要注意的是，Arrays.asList 方法返回的 ArrayList 并不是 <code>java.util.ArrayList</code>，它其实是 Arrays 类的一个内部类：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">class</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">E</span><span class="token punctuation">></span></span> <span class="token keyword">extends</span> <span class="token class-name">AbstractList</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">E</span><span class="token punctuation">></span></span>
<span class="token keyword">implements</span> <span class="token class-name">RandomAccess</span><span class="token punctuation">,</span> <span class="token class-name"><span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span>Serializable</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>如果需要添加元素或者删除元素的话，需要把它转成 <code>java.util.ArrayList</code>。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><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 class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">asList</span><span class="token punctuation">(</span>anArray<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></div><p>Java 8 新增了 Stream 流的概念，这就意味着我们也可以将数组转成 Stream 进行操作。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> anArray <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token punctuation">{</span><span class="token string">"沉默王二"</span><span class="token punctuation">,</span> <span class="token string">"一枚有趣的程序员"</span><span class="token punctuation">,</span> <span class="token string">"好好珍重他"</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span> aStream <span class="token operator">=</span> <span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span>anArray<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>如果想对数组进行排序的话，可以使用 Arrays 类提供的 <code>sort()</code> 方法。</p><ul><li>基本数据类型按照升序排列</li><li>实现了 Comparable 接口的对象按照 <code>compareTo()</code> 的排序</li></ul><p>来看第一个例子：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> anArray <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token punctuation">{</span><span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">8</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">sort</span><span class="token punctuation">(</span>anArray<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>排序后的结果如下所示：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">8</span><span class="token punctuation">]</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>来看第二个例子：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> yetAnotherArray <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token punctuation">{</span><span class="token string">"A"</span><span class="token punctuation">,</span> <span class="token string">"E"</span><span class="token punctuation">,</span> <span class="token string">"Z"</span><span class="token punctuation">,</span> <span class="token string">"B"</span><span class="token punctuation">,</span> <span class="token string">"C"</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">sort</span><span class="token punctuation">(</span>yetAnotherArray<span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span>
<span class="token class-name">Comparator</span><span class="token punctuation">.</span><span class="token function">comparing</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token operator">::</span><span class="token function">toString</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">reversed</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></div><p>只对 1-3 位置上的元素进行反序，所以结果如下所示：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>[A, Z, E, B, C]
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>有时候，我们需要从数组中查找某个具体的元素，最直接的方式就是通过遍历的方式：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> anArray <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token punctuation">{</span><span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">8</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> anArray<span class="token punctuation">.</span>length<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>anArray<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">==</span> <span class="token number">4</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token 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">"找到了 "</span> <span class="token operator">+</span> i<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">break</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>上例中从数组中查询元素 4，找到后通过 break 关键字退出循环。</p><p>如果数组提前进行了排序，就可以使用二分查找法，这样效率就会更高一些。<code>Arrays.binarySearch()</code> 方法可供我们使用，它需要传递一个数组，和要查找的元素。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> anArray <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> <span class="token punctuation">{</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token keyword">int</span> index <span class="token operator">=</span> <span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">binarySearch</span><span class="token punctuation">(</span>anArray<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></div><p>“除了一维数组，还有二维数组，三妹你可以去研究下，比如说用二维数组打印一下杨辉三角。”说完，我就去阳台上休息了，留三妹在那里学习，不能打扰她。</p><hr><p>GitHub 上标星 7600+ 的开源知识库《<a href="https://github.com/itwanger/toBeBetterJavaer" target="_blank" rel="noopener noreferrer">二哥的 Java 进阶之路<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>》第一版 PDF 终于来了！包括Java基础语法、数组&字符串、OOP、集合框架、Java IO、异常处理、Java 新特性、网络编程、NIO、并发编程、JVM等等，共计 32 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