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<meta name="keywords" content="Java, 基本数据类型, 缓存池, 内存优化, 缓存池原理, 缓存池应用, 缓存池实践"><meta property="og:url" content="https://javabetter.cn/basic-extra-meal/int-cache.html"><meta property="og:site_name" content="二哥的Java进阶之路"><meta property="og:title" content="Java基本数据类型缓存池剖析（IntegerCache）"><meta property="og:description" content="本文详细介绍了Java基本数据类型缓存池，包括其工作原理、应用场景以及如何使用缓存池提高内存利用效率。通过本文，您将了解到Java基本数据类型缓存池的优化策略和实践，掌握如何在实际开发中合理使用缓存池，提高程序性能。"><meta property="og:type" content="article"><meta property="og:locale" content="zh-CN"><meta property="og:updated_time" content="2023-09-04T05:16:42.000Z"><meta property="article:author" content="沉默王二"><meta property="article:tag" content="Java重要知识点"><meta property="article:modified_time" content="2023-09-04T05:16:42.000Z"><script type="application/ld+json">{"@context":"https://schema.org","@type":"Article","headline":"Java基本数据类型缓存池剖析（IntegerCache）","image":[""],"dateModified":"2023-09-04T05:16:42.000Z","author":[{"@type":"Person","name":"沉默王二","url":"/about-the-author/"}]}</script><meta name="robots" content="all"><meta name="author" content="沉默王二"><meta http-equiv="Cache-Control" content="no-cache, no-store, must-revalidate"><meta http-equiv="Pragma" content="no-cache"><meta http-equiv="Expires" content="0"><meta name="apple-mobile-web-app-capable" content="yes"><script>
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1.5M3.205 9.303c-.09.448-.277 1.21-1.241 1.203C1 10.5.5 9.513.5 8V7c0-1.57.5-2.5 1.464-2.494.964.006 1.134.598 1.24 1.342M12.553 10.5h1.953" stroke-width="1.2" stroke="currentColor" fill="none" stroke-linecap="square"></path></svg></kbd><kbd class="DocSearch-Button-Key">K</kbd></span></button></div><!--]--><!--]--><!--[--><!----><!--]--><button type="button" class="vp-toggle-navbar-button" aria-label="Toggle Navbar" aria-expanded="false" aria-controls="nav-screen"><span><span class="vp-top"></span><span class="vp-middle"></span><span class="vp-bottom"></span></span></button></div></header><!----><!--]--><!----><div class="toggle-sidebar-wrapper"><span class="arrow start"></span></div><aside id="sidebar" class="vp-sidebar"><!--[--><!----><!--]--><ul class="vp-sidebar-links"><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/home.html"><!---->一、前言<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable active" type="button"><!----><span class="vp-sidebar-title">二、Java基础</span><span class="vp-arrow down"></span></button><ul class="vp-sidebar-links"><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.1 Java概述及环境配置</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable active" type="button"><!----><span class="vp-sidebar-title">2.2 Java语法基础</span><span class="vp-arrow down"></span></button><ul class="vp-sidebar-links"><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/basic-extra-meal/48-keywords.html"><!---->Java关键字和保留字<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/basic-grammar/javadoc.html"><!---->Java注释<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/basic-grammar/basic-data-type.html"><!---->Java数据类型<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/basic-grammar/type-cast.html"><!---->Java数据类型转换<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link active vp-sidebar-link vp-sidebar-page active" href="/basic-extra-meal/int-cache.html"><!---->Java基本数据类型缓存池<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/basic-grammar/operator.html"><!---->Java运算符<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/basic-grammar/flow-control.html"><!---->Java流程控制语句<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li></ul></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.3 数组&字符串</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.4 面向对象编程</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.5 集合框架（容器）</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.6 Java IO</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.7 异常处理</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.8 常用工具类</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.9 Java新特性</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.10 网络编程</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.11 NIO</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.12 Java重要知识点</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.13 并发编程</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.14 JVM</span><span class="vp-arrow end"></span></button><!----></section></li></ul></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">三、Java进阶</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">四、MySQL</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">五、Redis</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">六、计算机基础</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">七、求职面试</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">八、学习建议</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">九、知识库搭建</span><span class="vp-arrow end"></span></button><!----></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">十、联系作者</span><span class="vp-arrow end"></span></button><!----></section></li></ul><!--[--><!----><!--]--></aside><!--[--><main id="main-content" class="vp-page"><!--[--><!----><!----><nav class="vp-breadcrumb disable"></nav><div class="vp-page-title"><h1><!---->Java基本数据类型缓存池剖析（IntegerCache）</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 tag3 clickable" role="navigation">Java重要知识点</span><!--]--><meta property="keywords" content="Java重要知识点"></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 1714 字</span><meta property="wordCount" content="1714"></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 6 分钟</span><meta property="timeRequired" content="PT6M"></span></div><hr></div><!----><!----><div class="theme-hope-content"><h1 id="_3-5-基本数据类型缓存池" tabindex="-1"><a class="header-anchor" href="#_3-5-基本数据类型缓存池" aria-hidden="true">#</a> 3.5 基本数据类型缓存池</h1><p>“三妹，今天我们来补一个小的知识点：Java 基本数据类型缓存池。”我喝了一口枸杞泡的茶后对三妹说，“考你一个问题哈：<code>new Integer(18) 与 Integer.valueOf(18)</code> 的区别是什么？”</p><p>“难道不一样吗？”三妹有点诧异。</p><p>“不一样的。”我笑着说。</p><ul><li><code>new Integer(18)</code> 每次都会新建一个对象;</li><li><code>Integer.valueOf(18)</code> 会使⽤用缓存池中的对象，多次调用只会取同⼀一个对象的引用。</li></ul><p>来看下面这段代码：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">Integer</span> x <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Integer</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 class-name">Integer</span> y <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Integer</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 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>x <span class="token operator">==</span> y<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Integer</span> z <span class="token operator">=</span> <span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token function">valueOf</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 class-name">Integer</span> k <span class="token operator">=</span> <span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token function">valueOf</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 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>z <span class="token operator">==</span> k<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Integer</span> m <span class="token operator">=</span> <span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span><span class="token number">300</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Integer</span> p <span class="token operator">=</span> <span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span><span class="token number">300</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>m <span class="token operator">==</span> p<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>来看一下输出结果吧：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>false
true
false
</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>“第一个 false，我知道原因，因为 new 出来的是不同的对象，地址不同。”三妹解释道，“第二个和第三个我认为都应该是 true 啊，为什么第三个会输出 false 呢？这个我理解不了。”</p><p>“其实原因也很简单。”我胸有成竹地说。</p><p>基本数据类型的包装类除了 Float 和 Double 之外，其他六个包装器类（Byte、Short、Integer、Long、Character、Boolean）都有常量缓存池。</p><ul><li>Byte：-128~127，也就是所有的 byte 值</li><li>Short：-128~127</li><li>Long：-128~127</li><li>Character：\u0000 - \u007F</li><li>Boolean：true 和 false</li></ul><p>拿 Integer 来举例子，Integer 类内部中内置了 256 个 Integer 类型的缓存数据，当使用的数据范围在 -128~127 之间时，会直接返回常量池中数据的引用，而不是创建对象，超过这个范围时会创建新的对象。</p><p>18 在 -128~127 之间，300 不在。</p><p>来看一下 valueOf 方法的源码吧。</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">static</span> <span class="token class-name">Integer</span> <span class="token function">valueOf</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>i <span class="token operator">>=</span><span class="token class-name">IntegerCache</span><span class="token punctuation">.</span>low <span class="token operator">&&</span> i <span class="token operator"><=</span><span class="token class-name">IntegerCache</span><span class="token punctuation">.</span>high<span class="token punctuation">)</span>
<span class="token keyword">return</span> <span class="token class-name">IntegerCache</span><span class="token punctuation">.</span>cache<span class="token punctuation">[</span>i <span class="token operator">+</span> <span class="token punctuation">(</span><span class="token operator">-</span><span class="token class-name">IntegerCache</span><span class="token punctuation">.</span>low<span class="token punctuation">)</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token class-name">Integer</span><span class="token punctuation">(</span>i<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></div><p>“哦，原来是因为 Integer.IntegerCache 这个内部类的原因啊！”三妹好像发现了新大陆。</p><p>“是滴。来看一下 IntegerCache 这个静态内部类的源码吧。”</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">IntegerCache</span> <span class="token punctuation">{</span>
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">int</span> low <span class="token operator">=</span> <span class="token operator">-</span><span class="token number">128</span><span class="token punctuation">;</span>
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">int</span> high<span class="token punctuation">;</span>
<span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">Integer</span> cache<span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword">static</span> <span class="token punctuation">{</span>
<span class="token comment">// high value may be configured by property</span>
<span class="token keyword">int</span> h <span class="token operator">=</span> <span class="token number">127</span><span class="token punctuation">;</span>
<span class="token class-name">String</span> integerCacheHighPropValue <span class="token operator">=</span>
sun<span class="token punctuation">.</span>misc<span class="token punctuation">.</span><span class="token constant">VM</span><span class="token punctuation">.</span><span class="token function">getSavedProperty</span><span class="token punctuation">(</span><span class="token string">"java.lang.Integer.IntegerCache.high"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>integerCacheHighPropValue <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">try</span> <span class="token punctuation">{</span>
<span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token function">parseInt</span><span class="token punctuation">(</span>integerCacheHighPropValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
i <span class="token operator">=</span> <span class="token class-name">Math</span><span class="token punctuation">.</span><span class="token function">max</span><span class="token punctuation">(</span>i<span class="token punctuation">,</span> <span class="token number">127</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// Maximum array size is Integer.MAX_VALUE</span>
h <span class="token operator">=</span> <span class="token class-name">Math</span><span class="token punctuation">.</span><span class="token function">min</span><span class="token punctuation">(</span>i<span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token constant">MAX_VALUE</span> <span class="token operator">-</span> <span class="token punctuation">(</span><span class="token operator">-</span>low<span class="token punctuation">)</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">catch</span><span class="token punctuation">(</span> <span class="token class-name">NumberFormatException</span> nfe<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token comment">// If the property cannot be parsed into an int, ignore it.</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
high <span class="token operator">=</span> h<span class="token punctuation">;</span>
cache <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Integer</span><span class="token punctuation">[</span><span class="token punctuation">(</span>high <span class="token operator">-</span> low<span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword">int</span> j <span class="token operator">=</span> low<span class="token punctuation">;</span>
<span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">int</span> k <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> k <span class="token operator"><</span> cache<span class="token punctuation">.</span>length<span class="token punctuation">;</span> k<span class="token operator">++</span><span class="token punctuation">)</span>
cache<span class="token punctuation">[</span>k<span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Integer</span><span class="token punctuation">(</span>j<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// range [-128, 127] must be interned (JLS7 5.1.7)</span>
<span class="token keyword">assert</span> <span class="token class-name">Integer<span class="token punctuation">.</span>IntegerCache</span><span class="token punctuation">.</span>high <span class="token operator">>=</span> <span class="token number">127</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">private</span> <span class="token class-name">IntegerCache</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 class="line-number"></div><div class="line-number"></div></div></div><p>详细解释下：当我们通过 <code>Integer.valueOf()</code> 方法获取整数对象时，会先检查该整数是否在 IntegerCache 中，如果在，则返回缓存中的对象，否则创建一个新的对象并缓存起来。</p><p>需要注意的是，如果使用 <code>new Integer()</code> 创建对象，即使值在 -128 到 127 范围内，也不会被缓存，每次都会创建新的对象。因此，推荐使用 <code>Integer.valueOf()</code> 方法获取整数对象。</p><p><a href="https://javabetter.cn/oo/static.html" target="_blank" rel="noopener noreferrer">学习 static 关键字<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>的时候，会详细解释静态代码块，你暂时先记住，三妹，静态代码块通常用来初始化一些静态变量，它会优先于 main() 方法执行。</p><p>在静态代码块中，low 为 -128，也就是缓存池的最小值；high 默认为 127，也就是缓存池的最大值，共计 256 个。</p><p><em>可以在 JVM 启动的时候，通过 <code>-XX:AutoBoxCacheMax=NNN</code> 来设置缓存池的大小，当然了，不能无限大，最大到 <code>Integer.MAX_VALUE -129</code></em></p><p>之后，初始化 cache 数组的大小，然后遍历填充，下标从 0 开始。</p><p>“明白了吧？三妹。”我喝了一口水后，扭头看了看旁边的三妹。</p><p>“这段代码不难理解，难理解的是 <code>assert Integer.IntegerCache.high >= 127;</code>，这行代码是干嘛的呀？”三妹很是不解。</p><p>“哦哦，你挺细心的呀！”三妹真不错，求知欲望越来越强烈了。</p><p>assert 是 Java 中的一个关键字，寓意是断言，为了方便调试程序，并不是发布程序的组成部分。</p><p>默认情况下，断言是关闭的，可以在命令行运行 Java 程序的时候加上 <code>-ea</code> 参数打开断言。</p><p>来看这段代码。</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">AssertTest</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">int</span> high <span class="token operator">=</span> <span class="token number">126</span><span class="token punctuation">;</span>
<span class="token keyword">assert</span> high <span class="token operator">>=</span> <span class="token number">127</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></div><p>假设手动设置的缓存池大小为 126，显然不太符合缓存池的预期值 127，结果会输出什么呢？</p><p>直接在 Intellij IDEA 中打开命令行终端，进入 classes 文件，执行：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code> /usr/libexec/java_home -v 1.8 --exec java -ea com.itwanger.s51.AssertTest
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p><em>我用的 macOS 环境，装了好多个版本的 JDK，该命令可以切换到 JDK 8</em></p><p>也可以不指定 Java 版本直接执行（加上 <code>-ea</code> 参数）：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>java -ea com.itwanger.s51.AssertTest
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>“呀，报错了呀。”三妹喊道。</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>Exception in thread "main" java.lang.AssertionError
at com.itwanger.s51.AssertTest.main(AssertTest.java:9)
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div></div></div><p>“是滴，因为 126 小于 127。”我回答道。</p><p>“原来 assert 是这样用的啊，我明白了。”三妹表示学会了。</p><p>在 Java 中，针对一些基本数据类型（如 Integer、Long、Boolean 等），Java 会在程序启动时创建一些常用的对象并缓存在内存中，以提高程序的性能和节省内存开销。这些常用对象被缓存在一个固定的范围内，超出这个范围的值会被重新创建新的对象。</p><p>使用数据类型缓存池可以有效提高程序的性能和节省内存开销，但需要注意的是，在特定的业务场景下，缓存池可能会带来一些问题，例如缓存池中的对象被不同的线程同时修改，导致数据错误等问题。因此，在实际开发中，需要根据具体的业务需求来决定是否使用数据类型缓存池。</p><hr><p>GitHub 上标星 9300+ 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 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