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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" type="button"><!----><span class="vp-sidebar-title">2.2 Java语法基础</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">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 active" type="button"><!----><a class="vp-link nav-link active vp-sidebar-title" href="/java8/"><!---->2.9 Java新特性<!----></a><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="/java8/stream.html"><!---->掌握Stream流<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/java8/optional.html"><!---->Optional最佳指南<!----></a><ul class="vp-sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a class="vp-link nav-link vp-sidebar-link vp-sidebar-page" href="/java8/Lambda.html"><!---->深入浅出Lambda表达式<!----></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="/java8/java14.html"><!---->Java 14 新特性<!----></a><ul class="vp-sidebar-sub-headers"><li class="vp-sidebar-sub-header"><a class="vp-link nav-link vp-sidebar-link vp-heading" href="/java8/java14.html#_01、下载-jdk-14"><!---->01、下载 JDK 14<!----></a><ul class="vp-sidebar-sub-headers"></ul></li><li class="vp-sidebar-sub-header"><a class="vp-link nav-link vp-sidebar-link vp-heading" href="/java8/java14.html#_02、升级-intellij-idea"><!---->02、升级 IntelliJ IDEA<!----></a><ul class="vp-sidebar-sub-headers"></ul></li><li class="vp-sidebar-sub-header"><a class="vp-link nav-link vp-sidebar-link vp-heading" href="/java8/java14.html#_01、instanceof"><!---->01、instanceof<!----></a><ul class="vp-sidebar-sub-headers"></ul></li><li class="vp-sidebar-sub-header"><a class="vp-link nav-link vp-sidebar-link vp-heading" href="/java8/java14.html#_02、records"><!---->02、Records<!----></a><ul class="vp-sidebar-sub-headers"></ul></li><li class="vp-sidebar-sub-header"><a class="vp-link nav-link vp-sidebar-link vp-heading" href="/java8/java14.html#_03、switch-表达式"><!---->03、switch 表达式<!----></a><ul class="vp-sidebar-sub-headers"></ul></li><li class="vp-sidebar-sub-header"><a class="vp-link nav-link vp-sidebar-link vp-heading" href="/java8/java14.html#_04、text-blocks"><!---->04、Text Blocks<!----></a><ul class="vp-sidebar-sub-headers"></ul></li></ul><!--]--></li></ul></section></li><li><section class="vp-sidebar-group"><button class="vp-sidebar-heading clickable" type="button"><!----><span class="vp-sidebar-title">2.10 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 14 开箱，新特性Record、instanceof、switch香香香香</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="2023-03-30T11:58:05.000Z"></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">Java新特性</span><!--]--><meta property="keywords" content="Java新特性"></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 2114 字</span><meta property="wordCount" content="2114"></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 7 分钟</span><meta property="timeRequired" content="PT7M"></span></div><hr></div><div class="toc-place-holder"><aside id="toc"><!--[--><!----><!--]--><div class="toc-header">此页内容<button type="button" class="print-button" title="打印"><svg xmlns="http://www.w3.org/2000/svg" class="icon print-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="print icon"><path d="M819.2 364.8h-44.8V128c0-17.067-14.933-32-32-32H281.6c-17.067 0-32 14.933-32 32v236.8h-44.8C145.067 364.8 96 413.867 96 473.6v192c0 59.733 49.067 108.8 108.8 108.8h44.8V896c0 17.067 14.933 32 32 32h460.8c17.067 0 32-14.933 32-32V774.4h44.8c59.733 0 108.8-49.067 108.8-108.8v-192c0-59.733-49.067-108.8-108.8-108.8zM313.6 160h396.8v204.8H313.6V160zm396.8 704H313.6V620.8h396.8V864zM864 665.6c0 25.6-19.2 44.8-44.8 44.8h-44.8V588.8c0-17.067-14.933-32-32-32H281.6c-17.067 0-32 14.933-32 32v121.6h-44.8c-25.6 0-44.8-19.2-44.8-44.8v-192c0-25.6 19.2-44.8 44.8-44.8h614.4c25.6 0 44.8 19.2 44.8 44.8v192z"></path></svg></button></div><div class="toc-wrapper"><ul class="toc-list"><!--[--><li class="toc-item"><a class="vp-link toc-link level3" href="/#_01、下载-jdk-14">01、下载 JDK 14</a></li><!----><!--]--><!--[--><li class="toc-item"><a class="vp-link toc-link level3" href="/#_02、升级-intellij-idea">02、升级 IntelliJ IDEA</a></li><!----><!--]--><!--[--><li class="toc-item"><a class="vp-link toc-link level3" href="/#_01、instanceof">01、instanceof</a></li><!----><!--]--><!--[--><li class="toc-item"><a class="vp-link toc-link level3" href="/#_02、records">02、Records</a></li><!----><!--]--><!--[--><li class="toc-item"><a class="vp-link toc-link level3" href="/#_03、switch-表达式">03、switch 表达式</a></li><!----><!--]--><!--[--><li class="toc-item"><a class="vp-link toc-link level3" href="/#_04、text-blocks">04、Text Blocks</a></li><!----><!--]--></ul><div class="toc-marker" style="top:-1.7rem;"></div></div><!--[--><!----><!--]--></aside></div><!----><div class="theme-hope-content"><h1 id="_10-4-java-14-新特性" tabindex="-1"><a class="header-anchor" href="#_10-4-java-14-新特性" aria-hidden="true">#</a> 10.4 Java 14 新特性</h1><p>Java 14 的时候，新增了记录 Record、模式匹配 instanceof 等新特性，转正了 Java 12 时的 switch 表达式，我们一起来过一遍。</p><figure><img src="https://imgconvert.csdnimg.cn/aHR0cHM6Ly91cGxvYWQtaW1hZ2VzLmppYW5zaHUuaW8vdXBsb2FkX2ltYWdlcy8xMTc5Mzg5LTA2N2E2NGZiZWY3OTU0MTAucG5n?x-oss-process=image/format,png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><h3 id="_01、下载-jdk-14" tabindex="-1"><a class="header-anchor" href="#_01、下载-jdk-14" aria-hidden="true">#</a> 01、下载 JDK 14</h3><blockquote><p>截止到2023年03月30日，Java 20 已经发布了，不过不是 LTS（长期支持）版本，Java 17、11、8 是目前提供支持的 LTS 版本。</p></blockquote><p>要想开箱，得先下载 JDK 14（如果你有更高版本，当然也可以），不然拿什么开箱呢，对吧？有 2 处地方可供下载，Oracle 上可以下载商用版， <a href="https://jdk.java.net/14/" target="_blank" rel="noopener noreferrer">jdk.java.net<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> 上可以下载开源版。我们就选择后者吧。</p><figure><img src="https://imgconvert.csdnimg.cn/aHR0cHM6Ly91cGxvYWQtaW1hZ2VzLmppYW5zaHUuaW8vdXBsb2FkX2ltYWdlcy8xMTc5Mzg5LTJkM2Q3MGQ4ODQ0NDk1MDEucG5n?x-oss-process=image/format,png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><p>我目前用的是 Windows 操作系统，所以就选择 Windows 版的 zip 包进行下载，完成后记得解压。</p><h3 id="_02、升级-intellij-idea" tabindex="-1"><a class="header-anchor" href="#_02、升级-intellij-idea" aria-hidden="true">#</a> 02、升级 IntelliJ IDEA</h3><blockquote><p>截止到 2023年03月30日，Intellij IDEA 的最新版本是 2023.1。</p></blockquote><p>需要把 IDEA 升级到抢先体验版 2020.1 EAP（如果你当前使用的版本大于此，当然也可以），否则无法支持 Java 14 的新特性。</p><figure><img src="https://imgconvert.csdnimg.cn/aHR0cHM6Ly91cGxvYWQtaW1hZ2VzLmppYW5zaHUuaW8vdXBsb2FkX2ltYWdlcy8xMTc5Mzg5LThhYjFjYmRiNDA3MjBiM2UucG5n?x-oss-process=image/format,png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><p>社区版的下载地址如下所示：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>[https://www.jetbrains.com/idea/nextversion/#section=windows](https://www.jetbrains.com/idea/nextversion/#section=windows)
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>安装的时候可以把之前的版本卸载，也可以选择保留。完成后，我们来新建一个 Java 14 的项目。</p><figure><img src="https://imgconvert.csdnimg.cn/aHR0cHM6Ly91cGxvYWQtaW1hZ2VzLmppYW5zaHUuaW8vdXBsb2FkX2ltYWdlcy8xMTc5Mzg5LTBhYWIwYWNiY2RiMzllZGIucG5n?x-oss-process=image/format,png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><h3 id="_01、instanceof" tabindex="-1"><a class="header-anchor" href="#_01、instanceof" aria-hidden="true">#</a> 01、instanceof</h3><p>按照新特性的顺序，我们就先从 instanceof 说起吧。旧式的 instanceof 的用法如下所示：</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">OldInstanceOf</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">Object</span> str <span class="token operator">=</span> <span class="token string">"Java 14，真香"</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>str <span class="token keyword">instanceof</span> <span class="token class-name">String</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">String</span> s <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">)</span>str<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>s<span class="token punctuation">.</span><span class="token function">length</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>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>需要先使用 instanceof 在 if 条件中判断 str 的类型是否为 String（第一步），再在 if 语句中将 str 强转为字符串类型（第二步），并且要重新声明一个变量用于强转后的赋值（第三步）。</p><p>三个步骤也不算多，但总觉得应该还有更好的语法，这不，Java 14 就想到了这一层。</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">NewInstanceOf</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">Object</span> str <span class="token operator">=</span> <span class="token string">"Java 14，真香"</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>str <span class="token keyword">instanceof</span> <span class="token class-name">String</span> s<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>s<span class="token punctuation">.</span><span class="token function">length</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>
<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></div><p>可以直接在 if 条件判断类型的时候添加一个变量，就不需要再强转和声明新的变量了。是不是特别简洁？但模式匹配的 instanceof 在 Java 14 中是预览版的，默认是不启用的，所以这段代码会有一个奇怪的编译错误（Java 14 中不支持模式匹配的 instanceof）。</p><figure><img src="https://imgconvert.csdnimg.cn/aHR0cHM6Ly91cGxvYWQtaW1hZ2VzLmppYW5zaHUuaW8vdXBsb2FkX2ltYWdlcy8xMTc5Mzg5LTg1MTQ4YWI3MjI2ZmM4ZTUucG5n?x-oss-process=image/format,png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><p>那怎么解决这个问题呢？需要在项目配置中手动设置一下语言的版本。</p><figure><img src="https://imgconvert.csdnimg.cn/aHR0cHM6Ly91cGxvYWQtaW1hZ2VzLmppYW5zaHUuaW8vdXBsb2FkX2ltYWdlcy8xMTc5Mzg5LTdhMzE3MDYwNjk5NTJmMDgucG5n?x-oss-process=image/format,png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><p>设置完成后，编译错误就随风飘走了。程序输出的结果如下所示：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>10
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>不错不错，真香。想知道 Java 编译器在背后帮我们做了什么吗？看一下反编译后的字节码就明白了。</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">NewInstanceOf</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token class-name">NewInstanceOf</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">Object</span> str <span class="token operator">=</span> <span class="token string">"Java 14，真香"</span><span class="token punctuation">;</span>
<span class="token class-name">String</span> s<span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>str <span class="token keyword">instanceof</span> <span class="token class-name">String</span> <span class="token operator">&&</span> <span class="token punctuation">(</span>s <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">)</span>str<span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">)</span>str<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>s<span class="token punctuation">.</span><span class="token function">length</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>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>在 if 条件判断前，先声明了变量 s，然后在 if 条件中进行了强转 <code>s = (String)str)</code>，并且判断了 s 和 str 是否相等。确实是一个解放开放者生产力的好特性，强烈希望这个特性在下个版本中转正。</p><h3 id="_02、records" tabindex="-1"><a class="header-anchor" href="#_02、records" aria-hidden="true">#</a> 02、Records</h3><p>在之前的一篇文章中，我谈到了<a href="https://javabetter.cn/basic-extra-meal/immutable.html" target="_blank" rel="noopener noreferrer">类的不可变性<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>，它是这样定义的：</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">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">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>age <span class="token operator">=</span> age<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">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 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>
<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></div><p>那么，对于 Records 来说，一条 Record 就代表一个不变的状态。尽管它会提供诸如 <code>equals()</code>、<code>hashCode()</code>、<code>toString()</code>、构造方法，以及字段的 getter，但它无意替代可变对象的类（没有 setter），以及 Lombok 提供的功能。</p><p>来用 Records 替代一下上面这个 Writer 类：</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">record</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 punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>你看，一行代码就搞定。关键是比之前的代码功能更丰富，来看一下反编译后的字节码：</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">final</span> <span class="token keyword">class</span> <span class="token class-name">Writer</span> <span class="token keyword">extends</span> <span class="token class-name"><span class="token namespace">java<span class="token punctuation">.</span>lang<span class="token punctuation">.</span></span>Record</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token class-name"><span class="token namespace">java<span class="token punctuation">.</span>lang<span class="token punctuation">.</span></span>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"><span class="token namespace">java<span class="token punctuation">.</span>lang<span class="token punctuation">.</span></span>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 comment">/* compiled code */</span> <span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token class-name"><span class="token namespace">java<span class="token punctuation">.</span>lang<span class="token punctuation">.</span></span>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 comment">/* compiled code */</span> <span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">final</span> <span class="token keyword">int</span> <span class="token function">hashCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">/* compiled code */</span> <span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">final</span> <span class="token keyword">boolean</span> <span class="token function">equals</span><span class="token punctuation">(</span><span class="token class-name"><span class="token namespace">java<span class="token punctuation">.</span>lang<span class="token punctuation">.</span></span>Object</span> o<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">/* compiled code */</span> <span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token class-name"><span class="token namespace">java<span class="token punctuation">.</span>lang<span class="token punctuation">.</span></span>String</span> <span class="token function">name</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">/* compiled code */</span> <span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">age</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">/* compiled code */</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></div><p>类是 final 的，字段是 private final 的，构造方法有两个参数，<code>toString()</code>、<code>hashCode()</code>、<code>equals()</code> 方法也有了，getter 方法也有了，只不过没有 get 前缀。但是没有 setter 方法，也就是说 Records 确实针对的是不可变对象——鉴定完毕。那怎么使用 Records 呢？</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">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>
<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><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">"toString："</span> <span class="token operator">+</span> writer<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">"hashCode："</span> <span class="token operator">+</span> writer<span class="token punctuation">.</span><span class="token function">hashCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"name："</span> <span class="token operator">+</span> writer<span class="token punctuation">.</span><span class="token function">name</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token 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">"age："</span> <span class="token operator">+</span> writer<span class="token punctuation">.</span><span class="token function">age</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Writer</span> writer1 <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><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">"equals："</span> <span class="token operator">+</span> <span class="token punctuation">(</span>writer<span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span>writer1<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 class="line-number"></div></div></div><p>程序输出的结果如下所示：</p><div class="language-text line-numbers-mode" data-ext="text"><pre class="language-text"><code>toString：Writer[name=沉默王二, age=18]
hashCode：1130697218
name：沉默王二
age：18
equals：true
</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>不错不错，真香，以后定义不可变类时就简单了，强烈希望这个特性在下个版本中转正。</p><h3 id="_03、switch-表达式" tabindex="-1"><a class="header-anchor" href="#_03、switch-表达式" aria-hidden="true">#</a> 03、switch 表达式</h3><p>关于 switch 表达式，我在之前的一篇文章中已经详细说明了，点击<a href="https://mp.weixin.qq.com/s/1BDDLDSKDGwQAfIFMyySdg" target="_blank" rel="noopener noreferrer">传送门<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>可以跳转过去看看。两周时间过去了，switch 表达式终于“媳妇熬成婆”，转正了，恭喜恭喜。</p><p>记得这篇文章发表到掘金的时候，被喷子各种无脑 diss，说：“还以为你有什么技巧，没想到用的是 Java 13，可我们还停留在 Java 8 啊！”这显然是一种固步自封的心态，非常不可取，程序员不应该这样。一个最简单的道理就是，Java 6 当年也很经典，不是被 Java 8 取代了吗？随着时间的推移，Java 8 早晚会被更划时代的新版本取代——总要进步嘛。</p><p>关于 switch 表达式，这里就简单地搬个例子给你瞧瞧：</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">SwitchDemo</span> <span class="token punctuation">{</span>
<span class="token keyword">enum</span> <span class="token class-name">PlayerTypes</span> <span class="token punctuation">{</span>
<span class="token constant">TENNIS</span><span class="token punctuation">,</span>
<span class="token constant">FOOTBALL</span><span class="token punctuation">,</span>
<span class="token constant">BASKETBALL</span><span class="token punctuation">,</span>
<span class="token constant">PINGPANG</span><span class="token punctuation">,</span>
<span class="token constant">UNKNOWN</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token function">createPlayer</span><span class="token punctuation">(</span><span class="token class-name">PlayerTypes</span><span class="token punctuation">.</span><span class="token constant">BASKETBALL</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">private</span> <span class="token keyword">static</span> <span class="token class-name">String</span> <span class="token function">createPlayer</span><span class="token punctuation">(</span><span class="token class-name">PlayerTypes</span> playerType<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> <span class="token keyword">switch</span> <span class="token punctuation">(</span>playerType<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">case</span> <span class="token constant">TENNIS</span> <span class="token operator">-></span> <span class="token string">"网球运动员费德勒"</span><span class="token punctuation">;</span>
<span class="token keyword">case</span> <span class="token constant">FOOTBALL</span> <span class="token operator">-></span> <span class="token string">"足球运动员C罗"</span><span class="token punctuation">;</span>
<span class="token keyword">case</span> <span class="token constant">BASKETBALL</span> <span class="token operator">-></span> <span class="token string">"篮球运动员詹姆斯"</span><span class="token punctuation">;</span>
<span class="token keyword">case</span> <span class="token constant">PINGPANG</span> <span class="token operator">-></span> <span class="token string">"乒乓球运动员马龙"</span><span class="token punctuation">;</span>
<span class="token keyword">case</span> <span class="token constant">UNKNOWN</span> <span class="token operator">-></span> <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">IllegalArgumentException</span><span class="token punctuation">(</span><span class="token string">"未知"</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>
<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>除了可以使用 <code>-></code> 的新式语法，还可以作为 return 结果，真香。</p><h3 id="_04、text-blocks" tabindex="-1"><a class="header-anchor" href="#_04、text-blocks" aria-hidden="true">#</a> 04、Text Blocks</h3><p>在文本块（Text Blocks）出现之前，如果我们需要拼接多行的字符串，就需要很多英文双引号和加号，看起来就好像老太婆的裹脚布，非常不雅。如果恰好要拼接一些 HTML 格式的文本（原生 SQL 也是如此）的话，还要通过空格进行排版，通过换行转义符 <code>\n</code> 进行换行，这些繁琐的工作对于一名开发人员来说，简直就是灾难。</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">OldTextBlock</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">String</span> html <span class="token operator">=</span> <span class="token string">"<html>\n"</span> <span class="token operator">+</span>
<span class="token string">" <body>\n"</span> <span class="token operator">+</span>
<span class="token string">" <p>Hello, world</p>\n"</span> <span class="token operator">+</span>
<span class="token string">" </body>\n"</span> <span class="token operator">+</span>
<span class="token string">"</html>\n"</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>html<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></div><p>Java 14 就完全不同了：</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">NewTextBlock</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">String</span> html <span class="token operator">=</span> <span class="token triple-quoted-string string">"""
<html>
<body>
<p>Hello, world</p>
</body>
</html>
"""</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>html<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>多余的英文双引号、加号、换行转义符，统统不见了。仅仅是通过前后三个英文双引号就实现了。我只能说，香，它真的香！</p><figure><img src="https://imgconvert.csdnimg.cn/aHR0cHM6Ly91cGxvYWQtaW1hZ2VzLmppYW5zaHUuaW8vdXBsb2FkX2ltYWdlcy8xMTc5Mzg5LTU3Njg1YmQzZDdmNzRkMDcuZ2lm" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><hr><p>GitHub 上标星 10000+ 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" 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