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class="button-bottom"></span></span></button></div></header><!----><!--]--><!----><div class="toggle-sidebar-wrapper"><span class="arrow left"></span></div><aside class="sidebar"><!--[--><!----><!--]--><ul class="sidebar-links"><li><!--[--><a href="/home.html" class="nav-link sidebar-link sidebar-page" aria-label="一、前言"><!---->一、前言<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable active"><!----><span class="title">二、Java核心</span><span class="arrow down"></span></button><ul class="sidebar-links"><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.1 Java概述</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.2 Java语法基础</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable active"><!----><span class="title">2.3 数组&字符串</span><span class="arrow down"></span></button><ul class="sidebar-links"><li><!--[--><a href="/array/array.html" class="nav-link sidebar-link sidebar-page" aria-label="Java数组"><!---->Java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 aria-current="page" href="/string/immutable.html" class="router-link-active router-link-exact-active nav-link active sidebar-link sidebar-page active" aria-label="为什么String是不可变的？"><!---->为什么String是不可变的？<!----></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="深入解析String.intern()方法"><!---->深入解析String.intern()方法<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/string/equals.html" class="nav-link sidebar-link sidebar-page" aria-label="如何判断两个字符串是否相等？"><!---->如何判断两个字符串是否相等？<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/string/join.html" class="nav-link sidebar-link sidebar-page" aria-label="Java字符串拼接"><!---->Java字符串拼接<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/string/split.html" class="nav-link sidebar-link sidebar-page" aria-label="Java字符串分割"><!---->Java字符串分割<!----></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 right"></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 right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.6 IO</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.7 异常处理</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.8 常用工具类</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.9 Java新特性</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.10 Java重要知识点</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.11 并发编程</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.12 JVM</span><span class="arrow right"></span></button><!----></section><!--]--></li></ul></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">三、Java企业级开发</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">四、数据库</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">五、计算机基础</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">六、求职面试</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">七、学习资源</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">八、学习建议</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">九、知识库搭建</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">十、联系作者</span><span class="arrow right"></span></button><!----></section><!--]--></li></ul><!--[--><!----><!--]--></aside><!--[--><main class="page" id="main-content"><!--[--><!----><nav class="breadcrumb disable"></nav><div class="page-title"><h1><!---->为什么String是不可变的？</h1><div class="page-info"><span class="author-info" aria-label="作者🖊" data-balloon-pos="down" isoriginal="false" pageview="false"><svg xmlns="http://www.w3.org/2000/svg" class="icon author-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="author icon"><path d="M649.6 633.6c86.4-48 147.2-144 147.2-249.6 0-160-128-288-288-288s-288 128-288 288c0 108.8 57.6 201.6 147.2 249.6-121.6 48-214.4 153.6-240 288-3.2 9.6 0 19.2 6.4 25.6 3.2 9.6 12.8 12.8 22.4 12.8h704c9.6 0 19.2-3.2 25.6-12.8 6.4-6.4 9.6-16 6.4-25.6-25.6-134.4-121.6-240-243.2-288z"></path></svg><span><a class="author-item" href="/about-the-author/" target="_blank" rel="noopener noreferrer">沉默王二</a></span><span property="author" content="沉默王二"></span></span><!----><span class="date-info" aria-label="写作日期📅" data-balloon-pos="down" isoriginal="false" pageview="false"><svg xmlns="http://www.w3.org/2000/svg" class="icon calendar-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="calendar icon"><path d="M716.4 110.137c0-18.753-14.72-33.473-33.472-33.473-18.753 0-33.473 14.72-33.473 33.473v33.473h66.993v-33.473zm-334.87 0c0-18.753-14.72-33.473-33.473-33.473s-33.52 14.72-33.52 33.473v33.473h66.993v-33.473zm468.81 33.52H716.4v100.465c0 18.753-14.72 33.473-33.472 33.473a33.145 33.145 0 01-33.473-33.473V143.657H381.53v100.465c0 18.753-14.72 33.473-33.473 33.473a33.145 33.145 0 01-33.473-33.473V143.657H180.6A134.314 134.314 0 0046.66 277.595v535.756A134.314 134.314 0 00180.6 947.289h669.74a134.36 134.36 0 00133.94-133.938V277.595a134.314 134.314 0 00-133.94-133.938zm33.473 267.877H147.126a33.145 33.145 0 01-33.473-33.473c0-18.752 14.72-33.473 33.473-33.473h736.687c18.752 0 33.472 14.72 33.472 33.473a33.145 33.145 0 01-33.472 33.473z"></path></svg><span>2021年10月22日</span><meta property="datePublished" content="2021-10-22T07:22:10.000Z"></span><span class="category-info" aria-label="分类🌈" data-balloon-pos="down" isoriginal="false" pageview="false"><svg xmlns="http://www.w3.org/2000/svg" class="icon category-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="category icon"><path d="M148.41 106.992h282.176c22.263 0 40.31 18.048 40.31 40.31V429.48c0 22.263-18.047 40.31-40.31 40.31H148.41c-22.263 0-40.311-18.047-40.311-40.31V147.302c0-22.263 18.048-40.31 40.311-40.31zM147.556 553.478H429.73c22.263 0 40.311 18.048 40.311 40.31v282.176c0 22.263-18.048 40.312-40.31 40.312H147.555c-22.263 0-40.311-18.049-40.311-40.312V593.79c0-22.263 18.048-40.311 40.31-40.311zM593.927 106.992h282.176c22.263 0 40.31 18.048 40.31 40.31V429.48c0 22.263-18.047 40.31-40.31 40.31H593.927c-22.263 0-40.311-18.047-40.311-40.31V147.302c0-22.263 18.048-40.31 40.31-40.31zM730.22 920.502H623.926c-40.925 0-74.22-33.388-74.22-74.425V623.992c0-41.038 33.387-74.424 74.425-74.424h222.085c41.038 0 74.424 33.226 74.424 74.067v114.233c0 10.244-8.304 18.548-18.547 18.548s-18.548-8.304-18.548-18.548V623.635c0-20.388-16.746-36.974-37.33-36.974H624.13c-20.585 0-37.331 16.747-37.331 37.33v222.086c0 20.585 16.654 37.331 37.126 37.331H730.22c10.243 0 18.547 8.304 18.547 18.547 0 10.244-8.304 18.547-18.547 18.547z"></path></svg><ul class="categories-wrapper"><li class="category category0 clickable" role="navigation">Java核心</li><meta property="articleSection" content="Java核心"></ul></span><span aria-label="标签🏷" data-balloon-pos="down" isoriginal="false" pageview="false"><svg xmlns="http://www.w3.org/2000/svg" class="icon tag-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="tag 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><ul class="tags-wrapper"><li class="tag tag5 clickable" role="navigation">数组&字符串</li></ul><meta property="keywords" content="数组&字符串"></span><span class="reading-time-info" aria-label="阅读时间⌛" data-balloon-pos="down" isoriginal="false" pageview="false"><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 5 分钟</span><meta property="timeRequired" content="PT5M"></span></div><hr></div><!----><!----><div class="theme-hope-content"><p>我正坐在沙发上津津有味地读刘欣大佬的《码农翻身》——Java 帝国这一章，门铃响了。起身打开门一看，是三妹，她从学校回来了。</p><p>“三妹，你回来的真及时，今天我们打算讲 Java 中的字符串呢。”等三妹换鞋的时候我说。</p><p>“哦，可以呀，哥。听说字符串的细节特别多，什么字符串常量池了、字符串不可变性了、字符串拼接了、字符串长度限制了等等，你最好慢慢讲，否则我可能一时半会消化不了。”三妹的态度显得很诚恳。</p><p>“嗯，我已经想好了，今天就只带你大概认识一下字符串，再说说为什么 String 是不可变的，其他的细节咱们后面再慢慢讲，保证你能及时消化。”</p><p>“好，那就开始吧。”三妹已经准备好坐在了电脑桌的边上。</p><p>我应了一声后走到电脑桌前坐下来，顺手打开 Intellij IDEA，并找到了 String 的源码。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token keyword">final</span> <span class="token keyword">class</span> <span class="token class-name">String</span>
<span class="token keyword">implements</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 class-name">Comparable</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">></span></span><span class="token punctuation">,</span> <span class="token class-name">CharSequence</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Stable</span>
<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> value<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">final</span> <span class="token keyword">byte</span> coder<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> hash<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>“第一，String 类是 final 的，意味着它不能被子类继承。”</p><p>“第二，String 类实现了 Serializable 接口，意味着它可以序列化。”</p><p>“第三，String 类实现了 Comparable 接口，意味着最好不要用‘==’来比较两个字符串是否相等，而应该用 <code>compareTo()</code> 方法去比较。”</p><p>“第四，StringBuffer、StringBuilder 和 String 一样，都实现了 CharSequence 接口，所以它们仨属于近亲。由于 String 是不可变的，所以遇到字符串拼接的时候就可以考虑一下 String 的另外两个好兄弟，StringBuffer 和 StringBuilder，它俩是可变的。”</p><p>“第五，Java 9 以前，<a href="https://tobebetterjavaer.com/basic-extra-meal/jdk9-char-byte-string.html" target="_blank" rel="noopener noreferrer">String 是用 char 型数组实现的，之后改成了 byte 型数组实现，并增加了 coder 来表示编码<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>。在 Latin1 字符为主的程序里，可以把 String 占用的内存减少一半。当然，天下没有免费的午餐，这个改进在节省内存的同时引入了编码检测的开销。”</p><p>“第六，每一个字符串都会有一个 hash 值，这个哈希值在很大概率是不会重复的，因此 String 很适合来作为 HashMap 的键值。”</p><p>“String 可能是 Java 中使用频率最高的引用类型了，因此 String 类的设计者可以说是用心良苦。”</p><p>比如说 String 的不可变性。</p><ul><li>String 类被 final 关键字修饰，所以它不会有子类，这就意味着没有子类可以重写它的方法，改变它的行为。</li><li>String 类的数据存储在 <code>byte[]</code> 数组中，而这个数组也被 final 关键字修饰了，这就表示 String 对象是没法被修改的，只要初始化一次，值就确定了。</li></ul><p>“哥，为什么要这样设计呢？”三妹有些不解。</p><p>“我先简单来说下，三妹，能懂最好，不能懂后面再细说。”</p><p>第一，可以保证 String 对象的安全性，避免被篡改，毕竟像密码这种隐私信息一般就是用字符串存储的。</p><p>第二，保证哈希值不会频繁变更。毕竟要经常作为哈希表的键值，经常变更的话，哈希表的性能就会很差劲。</p><p>第三，可以实现字符串常量池。</p><p>“由于字符串的不可变性，String 类的一些方法实现最终都返回了新的字符串对象。”等三妹稍微缓了一会后，我继续说到。</p><p>“就拿 <code>substring()</code> 方法来说。”</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token class-name">String</span> <span class="token function">substring</span><span class="token punctuation">(</span><span class="token keyword">int</span> beginIndex<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>beginIndex <span class="token operator"><</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">StringIndexOutOfBoundsException</span><span class="token punctuation">(</span>beginIndex<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">int</span> subLen <span class="token operator">=</span> <span class="token function">length</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> beginIndex<span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>subLen <span class="token operator"><</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">StringIndexOutOfBoundsException</span><span class="token punctuation">(</span>subLen<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>beginIndex <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">return</span> <span class="token function">isLatin1</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">?</span> <span class="token class-name">StringLatin1</span><span class="token punctuation">.</span><span class="token function">newString</span><span class="token punctuation">(</span>value<span class="token punctuation">,</span> beginIndex<span class="token punctuation">,</span> subLen<span class="token punctuation">)</span>
<span class="token operator">:</span> <span class="token class-name">StringUTF16</span><span class="token punctuation">.</span><span class="token function">newString</span><span class="token punctuation">(</span>value<span class="token punctuation">,</span> beginIndex<span class="token punctuation">,</span> subLen<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">// StringLatin1.newString </span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token class-name">String</span> <span class="token function">newString</span><span class="token punctuation">(</span><span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> val<span class="token punctuation">,</span> <span class="token keyword">int</span> index<span class="token punctuation">,</span> <span class="token keyword">int</span> len<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">String</span><span class="token punctuation">(</span><span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">copyOfRange</span><span class="token punctuation">(</span>val<span class="token punctuation">,</span> index<span class="token punctuation">,</span> index <span class="token operator">+</span> len<span class="token punctuation">)</span><span class="token punctuation">,</span>
LATIN1<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">// UTF16.newString</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token class-name">String</span> <span class="token function">newString</span><span class="token punctuation">(</span><span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> val<span class="token punctuation">,</span> <span class="token keyword">int</span> index<span class="token punctuation">,</span> <span class="token keyword">int</span> len<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">.</span>COMPACT_STRINGS<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> buf <span class="token operator">=</span> <span class="token function">compress</span><span class="token punctuation">(</span>val<span class="token punctuation">,</span> index<span class="token punctuation">,</span> len<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>buf <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">return</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span>buf<span class="token punctuation">,</span> LATIN1<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword">int</span> last <span class="token operator">=</span> index <span class="token operator">+</span> len<span class="token punctuation">;</span>
<span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span><span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">copyOfRange</span><span class="token punctuation">(</span>val<span class="token punctuation">,</span> index <span class="token operator"><<</span> <span class="token number">1</span><span class="token punctuation">,</span> last <span class="token operator"><<</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">,</span> UTF16<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></div><p><code>substring()</code> 方法用于截取字符串，不管是 Latin1 字符还是 UTF16 字符，最终返回的都是 new 出来的新字符串对象。</p><p>“还有 <code>concat()</code> 方法。”</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token keyword">public</span> <span class="token class-name">String</span> <span class="token function">concat</span><span class="token punctuation">(</span><span class="token class-name">String</span> str<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">int</span> olen <span class="token operator">=</span> str<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 keyword">if</span> <span class="token punctuation">(</span>olen <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">coder</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> str<span class="token punctuation">.</span><span class="token function">coder</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">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> val <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span>value<span class="token punctuation">;</span>
<span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> oval <span class="token operator">=</span> str<span class="token punctuation">.</span>value<span class="token punctuation">;</span>
<span class="token keyword">int</span> len <span class="token operator">=</span> val<span class="token punctuation">.</span>length <span class="token operator">+</span> oval<span class="token punctuation">.</span>length<span class="token punctuation">;</span>
<span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> buf <span class="token operator">=</span> <span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">copyOf</span><span class="token punctuation">(</span>val<span class="token punctuation">,</span> len<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">arraycopy</span><span class="token punctuation">(</span>oval<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> buf<span class="token punctuation">,</span> val<span class="token punctuation">.</span>length<span class="token punctuation">,</span> oval<span class="token punctuation">.</span>length<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">String</span><span class="token punctuation">(</span>buf<span class="token punctuation">,</span> coder<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">int</span> len <span class="token operator">=</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 keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> buf <span class="token operator">=</span> <span class="token class-name">StringUTF16</span><span class="token punctuation">.</span><span class="token function">newBytesFor</span><span class="token punctuation">(</span>len <span class="token operator">+</span> olen<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">getBytes</span><span class="token punctuation">(</span>buf<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> UTF16<span class="token punctuation">)</span><span class="token punctuation">;</span>
str<span class="token punctuation">.</span><span class="token function">getBytes</span><span class="token punctuation">(</span>buf<span class="token punctuation">,</span> len<span class="token punctuation">,</span> UTF16<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">String</span><span class="token punctuation">(</span>buf<span class="token punctuation">,</span> UTF16<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></div><p><code>concat()</code> 方法用于拼接字符串，不管编码是否一致，最终也返回的是新的字符串对象。</p><p>“<code>replace()</code> 替换方法其实也一样，三妹，你可以自己一会看一下源码，也是返回新的字符串对象。”</p><p>“这就意味着，不管是截取、拼接，还是替换，都不是在原有的字符串上进行的，而是重新生成了新的字符串对象。也就是说，这些操作执行过后，<strong>原来的字符串对象并没有发生改变</strong>。”</p><p>“三妹，你记住，String 对象一旦被创建后就固定不变了，对 String 对象的任何修改都不会影响到原来的字符串对象，都会生成新的字符串对象。”</p><p>“嗯嗯，记住了，哥。”三妹很乖。</p><p>“那今天就先讲到这吧，后面我们再对每一个细分领域深入地展开一下。你可以找一些资料先预习下，我出去散会心。。。。。”</p><p><img src="http://cdn.tobebetterjavaer.com/tobebetterjavaer/images/xingbiaogongzhonghao.png" alt=""></p></div><!----><footer class="page-meta"><div class="meta-item edit-link"><a href="https://github.com/itwanger/toBeBetterJavaer/edit/master/docs/string/immutable.md" rel="noopener noreferrer" target="_blank" aria-label="在 GitHub 上编辑此页" class="nav-link label"><!--[--><svg xmlns="http://www.w3.org/2000/svg" class="icon edit-icon" viewbox="0 0 1024 1024" fill="currentColor" aria-label="edit icon"><path d="M430.818 653.65a60.46 60.46 0 0 1-50.96-93.281l71.69-114.012 7.773-10.365L816.038 80.138A60.46 60.46 0 0 1 859.225 62a60.46 60.46 0 0 1 43.186 18.138l43.186 43.186a60.46 60.46 0 0 1 0 86.373L588.879 565.55l-8.637 8.637-117.466 68.234a60.46 60.46 0 0 1-31.958 11.229z"></path><path d="M728.802 962H252.891A190.883 190.883 0 0 1 62.008 771.98V296.934a190.883 190.883 0 0 1 190.883-192.61h267.754a60.46 60.46 0 0 1 0 120.92H252.891a69.962 69.962 0 0 0-69.098 69.099V771.98a69.962 69.962 0 0 0 69.098 69.098h475.911A69.962 69.962 0 0 0 797.9 771.98V503.363a60.46 60.46 0 1 1 120.922 0V771.98A190.883 190.883 0 0 1 728.802 962z"></path></svg><!--]-->在 GitHub 上编辑此页<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewbox="0 0 100 100" width="15" height="15"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path><polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg><span class="external-link-icon-sr-only">open in new window</span></span><!----></a></div><div class="meta-item update-time"><span class="label">上次编辑于: </span><span class="info">2022/7/28 下午1:05:53</span></div><div class="meta-item contributors"><span class="label">贡献者: </span><!--[--><!--[--><span class="contributor" title="email: www.qing_gee@163.com">itwanger</span>,<!--]--><!--[--><span class="contributor" title="email: www.qing_gee@163.com">沉默王二</span><!--]--><!--]--></div></footer><nav class="page-nav"><a href="/array/print.html" class="nav-link prev" aria-label="打印Java数组"><div class="hint"><span class="arrow left"></span>上一页</div><div class="link"><!---->打印Java数组</div></a><a href="/string/constant-pool.html" class="nav-link next" aria-label="深入理解Java字符串常量池"><div class="hint">下一页<span class="arrow right"></span></div><div class="link">深入理解Java字符串常量池<!----></div></a></nav><div class="giscus-wrapper input-top" style="display:block;">Loading...</div><!----><!--]--></main><!--]--><footer class="footer-wrapper"><div class="footer"><a href="https://beian.miit.gov.cn/" target="_blank">豫ICP备2021038026号-1</a><img src="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/beian.png" height="15px" width="15px" /><a target="_blank" href="http://www.beian.gov.cn/portal/registerSystemInfo?recordcode=41030502000411"><span>豫公网安备 41030502000411号</span></a></div><div class="copyright">Copyright © 2022 沉默王二</div></footer><!--]--></div><!--]--><!----><!----><!--]--></div>
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