toBeBetterJavaer/dist/string/equals.html at master · henrylanggithub/toBeBetterJavaer

History

130 lines (125 loc) · 56.8 KB

Raw

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

<!DOCTYPE html>

<head>

var _hmt = _hmt || [];

(function() {

var hm = document.createElement("script");

hm.src = "https://hm.baidu.com/hm.js?5230ac143650bf5eb3c14f3fb9b1d3ec";

var s = document.getElementsByTagName("script")[0];

s.parentNode.insertBefore(hm, s);

})();

</script><link rel="stylesheet" href="//at.alicdn.com/t/font_3180624_7cy10l7jqqh.css"><link rel="icon" href="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/favicon.ico"><link rel="icon" href="/assets/icon/chrome-mask-512.png" type="image/png" sizes="512x512"><link rel="icon" href="/assets/icon/chrome-mask-192.png" type="image/png" sizes="192x192"><link rel="icon" href="/assets/icon/chrome-512.png" type="image/png" sizes="512x512"><link rel="icon" href="/assets/icon/chrome-192.png" type="image/png" sizes="192x192"><link rel="manifest" href="/manifest.webmanifest" crossorigin="use-credentials"><meta name="theme-color" content="#096dd9"><link rel="apple-touch-icon" href="/assets/icon/apple-icon-152.png"><meta name="apple-mobile-web-app-status-bar-style" content="black"><meta name="msapplication-TileImage" content="/assets/icon/ms-icon-144.png"><meta name="msapplication-TileColor" content="#ffffff"><meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no, viewport-fit=cover"><title>Java如何判断两个字符串是否相等？ | Java程序员进阶之路</title><meta name="description" content="Java程序员进阶之路，小白的零基础Java教程，从入门到进阶，Java如何判断两个字符串是否相等？">

<style>

:root {

--bg-color: #fff;

}

html[data-theme="dark"] {

--bg-color: #1d2025;

}

html,

body {

background: var(--bg-color);

}

</style>

const userMode = localStorage.getItem("vuepress-theme-hope-scheme");

const systemDarkMode =

window.matchMedia &&

window.matchMedia("(prefers-color-scheme: dark)").matches;

if (userMode === "dark" || (userMode !== "light" && systemDarkMode)) {

document.querySelector("html").setAttribute("data-theme", "dark");

}

</script>

</head>

<body>

<div id="app"><span tabindex="-1"></span><a href="#main-content" class="skip-link sr-only">Skip to content</a><div class="theme-container has-toc"><header class="navbar"><div class="navbar-left"><button class="toggle-sidebar-button" title="Toggle Sidebar"><span class="icon"></span></button><a href="/" class="brand"><img class="logo" src="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/logo-02.png" alt="Java程序员进阶之路"><span class="site-name hide-in-pad">Java程序员进阶之路</span></a></div><div class="navbar-center"><nav class="nav-links"><div class="nav-item hide-in-mobile"><a href="/blog.html" class="nav-link" aria-label="博客"><span class="icon iconfont icon-gaishu"></span>博客</a></div><div class="nav-item hide-in-mobile"><a href="/home.html" class="nav-link" aria-label="进阶之路"><span class="icon iconfont icon-lujing"></span>进阶之路</a></div><div class="nav-item hide-in-mobile"><a href="/zhishixingqiu/" class="nav-link" aria-label="知识星球"><span class="icon iconfont icon-Artboard"></span>知识星球</a></div><div class="nav-item hide-in-mobile"><a href="/xuexiluxian/" class="nav-link" aria-label="学习路线"><span class="icon iconfont icon-luxian"></span>学习路线</a></div><div class="nav-item hide-in-mobile"><div class="dropdown-wrapper"><button class="dropdown-title" type="button" aria-label="珍藏资源"><span class="title"><span class="icon iconfont icon-youzhi"></span>珍藏资源</span><span class="arrow"></span><ul class="nav-dropdown"><li class="dropdown-item"><a href="/pdf/" class="nav-link" aria-label="PDF下载"><span class="icon iconfont icon-java"></span>PDF下载</a></li><li class="dropdown-item"><a href="/sidebar/sanfene/nixi.html" class="nav-link" aria-label="面渣逆袭"><span class="icon iconfont icon-zhunbei"></span>面渣逆袭</a></li><li class="dropdown-item"><a href="/nice-article/itmind/" class="nav-link" aria-label="破解合集"><span class="icon iconfont icon-zhongyaotishi"></span>破解合集</a></li></ul></button></div></div><div class="nav-item hide-in-mobile"><a href="https://space.bilibili.com/513340480" rel="noopener noreferrer" target="_blank" aria-label="B站视频" class="nav-link"><span class="icon iconfont icon-bzhan"></span>B站视频<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></nav></div><div class="navbar-right"><div class="nav-item"><a class="repo-link" href="https://github.com/itwanger/toBeBetterJavaer" target="_blank" rel="noopener noreferrer" aria-label="GitHub"><svg xmlns="http://www.w3.org/2000/svg" class="icon github-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="github icon" style="width:1.25rem;height:1.25rem;vertical-align:middle;"><path d="M511.957 21.333C241.024 21.333 21.333 240.981 21.333 512c0 216.832 140.544 400.725 335.574 465.664 24.49 4.395 32.256-10.07 32.256-23.083 0-11.69.256-44.245 0-85.205-136.448 29.61-164.736-64.64-164.736-64.64-22.315-56.704-54.4-71.765-54.4-71.765-44.587-30.464 3.285-29.824 3.285-29.824 49.195 3.413 75.179 50.517 75.179 50.517 43.776 75.008 114.816 53.333 142.762 40.79 4.523-31.66 17.152-53.377 31.19-65.537-108.971-12.458-223.488-54.485-223.488-242.602 0-53.547 19.114-97.323 50.517-131.67-5.035-12.33-21.93-62.293 4.779-129.834 0 0 41.258-13.184 134.912 50.346a469.803 469.803 0 0 1 122.88-16.554c41.642.213 83.626 5.632 122.88 16.554 93.653-63.488 134.784-50.346 134.784-50.346 26.752 67.541 9.898 117.504 4.864 129.834 31.402 34.347 50.474 78.123 50.474 131.67 0 188.586-114.73 230.016-224.042 242.09 17.578 15.232 33.578 44.672 33.578 90.454v135.85c0 13.142 7.936 27.606 32.854 22.87C862.25 912.597 1002.667 728.747 1002.667 512c0-271.019-219.648-490.667-490.71-490.667z"></path></svg></a></div><div class="nav-item hide-in-mobile"><button class="outlook-button" tabindex="-1" ariahidden="true"><svg xmlns="http://www.w3.org/2000/svg" class="icon outlook-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="outlook icon"><path d="M224 800c0 9.6 3.2 44.8 6.4 54.4 6.4 48-48 76.8-48 76.8s80 41.6 147.2 0 134.4-134.4 38.4-195.2c-22.4-12.8-41.6-19.2-57.6-19.2C259.2 716.8 227.2 761.6 224 800zM560 675.2l-32 51.2c-51.2 51.2-83.2 32-83.2 32 25.6 67.2 0 112-12.8 128 25.6 6.4 51.2 9.6 80 9.6 54.4 0 102.4-9.6 150.4-32l0 0c3.2 0 3.2-3.2 3.2-3.2 22.4-16 12.8-35.2 6.4-44.8-9.6-12.8-12.8-25.6-12.8-41.6 0-54.4 60.8-99.2 137.6-99.2 6.4 0 12.8 0 22.4 0 12.8 0 38.4 9.6 48-25.6 0-3.2 0-3.2 3.2-6.4 0-3.2 3.2-6.4 3.2-6.4 6.4-16 6.4-16 6.4-19.2 9.6-35.2 16-73.6 16-115.2 0-105.6-41.6-198.4-108.8-268.8C704 396.8 560 675.2 560 675.2zM224 419.2c0-28.8 22.4-51.2 51.2-51.2 28.8 0 51.2 22.4 51.2 51.2 0 28.8-22.4 51.2-51.2 51.2C246.4 470.4 224 448 224 419.2zM320 284.8c0-22.4 19.2-41.6 41.6-41.6 22.4 0 41.6 19.2 41.6 41.6 0 22.4-19.2 41.6-41.6 41.6C339.2 326.4 320 307.2 320 284.8zM457.6 208c0-12.8 12.8-25.6 25.6-25.6 12.8 0 25.6 12.8 25.6 25.6 0 12.8-12.8 25.6-25.6 25.6C470.4 233.6 457.6 220.8 457.6 208zM128 505.6C128 592 153.6 672 201.6 736c28.8-60.8 112-60.8 124.8-60.8-16-51.2 16-99.2 16-99.2l316.8-422.4c-48-19.2-99.2-32-150.4-32C297.6 118.4 128 291.2 128 505.6zM764.8 86.4c-22.4 19.2-390.4 518.4-390.4 518.4-22.4 28.8-12.8 76.8 22.4 99.2l9.6 6.4c35.2 22.4 80 12.8 99.2-25.6 0 0 6.4-12.8 9.6-19.2 54.4-105.6 275.2-524.8 288-553.6 6.4-19.2-3.2-32-19.2-32C777.6 76.8 771.2 80 764.8 86.4z"></path></svg><div class="outlook-dropdown"></div></button></div><div id="docsearch-container"></div><button class="toggle-navbar-button" aria-label="Toggle Navbar" aria-expanded="false" aria-controls="nav-screen"><span class="button-container"><span class="button-top"></span><span class="button-middle"></span><span class="button-bottom"></span></span></button></div></header><div class="toggle-sidebar-wrapper"><span class="arrow 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 href="/string/immutable.html" class="nav-link sidebar-link sidebar-page" 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 aria-current="page" href="/string/equals.html" class="router-link-active router-link-exact-active nav-link active sidebar-link sidebar-page active" 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 网络编程</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">2.12 NIO</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">2.13 并发编程</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">2.14 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、学习建议</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">八、知识库搭建</span><span class="arrow right"></span></button></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><span class="title">九、联系作者</span><span class="arrow right"></span></button></section></li></ul></aside><main class="page" id="main-content"><nav class="breadcrumb disable"></nav><div class="page-title"><h1>Java如何判断两个字符串是否相等？</h1><div class="page-info"><span class="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="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"><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7月13日</span><meta property="datePublished" content="2021-07-13T07:01:13.000Z"></span><span class="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><ul class="categories-wrapper"><li><span class="category category0 clickable" role="navigation">Java核心</span></li></ul><meta property="articleSection" content="Java核心"></span><span 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><ul class="tags-wrapper"><li><span class="tag tag5 clickable" role="navigation">数组&字符串</span></li></ul><meta property="keywords" content="数组&字符串"></span><span class="words-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 1981 字</span><meta property="wordCount" content="1981"></span><span class="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="theme-hope-content"><p>“二哥，如何比较两个字符串相等啊？”三妹问。</p><p>“这个问题看似简单，却在 Stack Overflow 上有超过 370 万+的访问量。”我说，“这个问题也可以引申为 <code>.equals()</code> 和 ‘==’ 操作符有什么区别。”</p><ul><li>“==”操作符用于比较两个对象的地址是否相等。</li><li><code>.equals()</code> 方法用于比较两个对象的内容是否相等。</li></ul><p>“不是很理解。”三妹感到很困惑。</p><p>“我来举个不恰当又很恰当的例子，一看你就明白了，三妹。”</p><p>有一对双胞胎，姐姐叫阿丽塔，妹妹叫洛丽塔。我们普通人可能完全无法分辨谁是姐姐谁是妹妹，可她们的妈妈却可以轻而易举地辨认出。</p><p><img src="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/string/equals-01.png" alt="" loading="lazy"></p><p><code>.equals()</code> 就好像我们普通人，看见阿丽塔以为是洛丽塔，看见洛丽塔以为是阿丽塔，看起来一样就觉得她们是同一个人；“==”操作符就好像她们的妈妈，要求更严格，观察更细致，一眼就能分辨出谁是姐姐谁是妹妹。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">String</span> alita <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span><span class="token string">"小萝莉"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token class-name">String</span> luolita <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span><span class="token string">"小萝莉"</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>alita<span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span>luolita<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</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>alita <span class="token operator">==</span> luolita<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</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>就上面这段代码来说，<code>.equals()</code> 输出的结果为 true，而“==”操作符输出的结果为 false——前者要求内容相等就可以，后者要求必须是同一个对象。</p><p>“三妹，之前已经学过了，Java 的所有类都默认地继承 Object 这个超类，该类有一个名为 <code>.equals()</code> 的方法。”一边说，我一边打开了 Object 类的源码。</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">boolean</span> <span class="token function">equals</span><span class="token punctuation">(</span><span class="token class-name">Object</span> obj<span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token keyword">this</span> <span class="token operator">==</span> obj<span class="token punctuation">)</span><span class="token punctuation">;</span>

</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>你看，Object 类的 <code>.equals()</code> 方法默认采用的是“==”操作符进行比较。假如子类没有重写该方法的话，那么“==”操作符和 <code>.equals()</code> 方法的功效就完全一样——比较两个对象的内存地址是否相等。</p><p>但实际情况中，有不少类重写了 <code>.equals()</code> 方法，因为比较内存地址的要求比较严格，不太符合现实中所有的场景需求。拿 String 类来说，我们在比较字符串的时候，的确只想判断它们俩的内容是相等的就可以了，并不想比较它们俩是不是同一个对象。</p><p>况且，字符串有字符串常量池的概念，本身就推荐使用 <code>String s = "字符串"</code> 这种形式来创建字符串对象，而不是通过 new 关键字的方式，因为可以把字符串缓存在字符串常量池中，方便下次使用。</p><p>“哦，我明白了。”三妹说。</p><p>“那就来看一下 <code>.equals()</code> 方法的源码吧。”我说。</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">boolean</span> <span class="token function">equals</span><span class="token punctuation">(</span><span class="token class-name">Object</span> anObject<span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">this</span> <span class="token operator">==</span> anObject<span class="token punctuation">)</span> <span class="token punctuation">{</span>

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

<span class="token keyword">if</span> <span class="token punctuation">(</span>anObject <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> aString <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">)</span>anObject<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> aString<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">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">equals</span><span class="token punctuation">(</span>value<span class="token punctuation">,</span> aString<span class="token punctuation">.</span>value<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">equals</span><span class="token punctuation">(</span>value<span class="token punctuation">,</span> aString<span class="token punctuation">.</span>value<span class="token punctuation">)</span><span class="token punctuation">;</span>

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

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">boolean</span> <span class="token function">equals</span><span class="token punctuation">(</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">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> other<span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">if</span> <span class="token punctuation">(</span>value<span class="token punctuation">.</span>length <span class="token operator">==</span> other<span class="token punctuation">.</span>length<span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> value<span class="token punctuation">.</span>length<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">if</span> <span class="token punctuation">(</span>value<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">!=</span> other<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

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

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

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

</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>“输出什么呢？”我问。</p><p>“<code>.equals()</code> 比较的是两个字符串对象的内容是否相等，所以结果为 true。”三妹答。</p><p>第二题：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span><span class="token string">"小萝莉"</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token string">"小萝莉"</span>

</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>“==操作符左侧的是在堆中创建的对象，右侧是在字符串常量池中的对象，尽管内容相同，但内存地址不同，所以返回 false。”三妹答。</p><p>第三题：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span><span class="token string">"小萝莉"</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span><span class="token string">"小萝莉"</span><span class="token punctuation">)</span>

</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>“new 出来的对象肯定是完全不同的内存地址，所以返回 false。”三妹答。</p><p>第四题：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token string">"小萝莉"</span> <span class="token operator">==</span> <span class="token string">"小萝莉"</span>

</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>“字符串常量池中只会有一个相同内容的对象，所以返回 true。”三妹答。</p><p>第五题：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token string">"小萝莉"</span> <span class="token operator">==</span> <span class="token string">"小"</span> <span class="token operator">+</span> <span class="token string">"萝莉"</span>

</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>“由于‘小’和‘萝莉’都在字符串常量池，所以编译器在遇到‘+’操作符的时候将其自动优化为“小萝莉”，所以返回 true。”</p><p>第六题：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span><span class="token string">"小萝莉"</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">intern</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token string">"小萝莉"</span>

</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>“<code>new String("小萝莉")</code> 在执行的时候，会先在字符串常量池中创建对象，然后再在堆中创建对象；执行 <code>intern()</code> 方法的时候发现字符串常量池中已经有了‘小萝莉’这个对象，所以就直接返回字符串常量池中的对象引用了，那再与字符串常量池中的‘小萝莉’比较，当然会返回 true 了。”三妹说。</p><p>哇，不得不说，三妹前几节的字符串相关内容都完全学会了呀！</p><p>“三妹，哥再给你补充一点。”我说。</p><p>“如果要进行两个字符串对象的内容比较，除了 <code>.equals()</code> 方法，还有其他两个可选的方案。”</p><p>1）<code>Objects.equals()</code></p><p><code>Objects.equals()</code> 这个静态方法的优势在于不需要在调用之前判空。</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 keyword">boolean</span> <span class="token function">equals</span><span class="token punctuation">(</span><span class="token class-name">Object</span> a<span class="token punctuation">,</span> <span class="token class-name">Object</span> b<span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">return</span> <span class="token punctuation">(</span>a <span class="token operator">==</span> b<span class="token punctuation">)</span> <span class="token operator">||</span> <span class="token punctuation">(</span>a <span class="token operator">!=</span> <span class="token keyword">null</span> <span class="token operator">&&</span> a<span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span>b<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>如果直接使用 <code>a.equals(b)</code>，则需要在调用之前对 a 进行判空，否则可能会抛出空指针 <code>java.lang.NullPointerException</code>。<code>Objects.equals()</code> 用起来就完全没有这个担心。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">Objects</span><span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span><span class="token string">"小萝莉"</span><span class="token punctuation">,</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span><span class="token string">"小"</span> <span class="token operator">+</span> <span class="token string">"萝莉"</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token comment">// --> true</span>

<span class="token class-name">Objects</span><span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span><span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span><span class="token string">"小"</span> <span class="token operator">+</span> <span class="token string">"萝莉"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// --> false</span>

<span class="token class-name">String</span> a <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>

a<span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span><span class="token string">"小"</span> <span class="token operator">+</span> <span class="token string">"萝莉"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// throw exception</span>

<span class="token comment">// Argument is a StringBuffer, StringBuilder</span>

<span class="token keyword">if</span> <span class="token punctuation">(</span>cs <span class="token keyword">instanceof</span> <span class="token class-name">AbstractStringBuilder</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">if</span> <span class="token punctuation">(</span>cs <span class="token keyword">instanceof</span> <span class="token class-name">StringBuffer</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">synchronized</span><span class="token punctuation">(</span>cs<span class="token punctuation">)</span> <span class="token punctuation">{</span>

<span class="token keyword">return</span> <span class="token function">nonSyncContentEquals</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token class-name">AbstractStringBuilder</span><span class="token punctuation">)</span>cs<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">// Argument is a String</span>

<span class="token keyword">if</span> <span class="token punctuation">(</span>cs <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 keyword">return</span> <span class="token function">equals</span><span class="token punctuation">(</span>cs<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">// Argument is a generic CharSequence</span>

<span class="token keyword">int</span> n <span class="token operator">=</span> cs<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>n <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 punctuation">{</span>

<span class="token keyword">return</span> <span class="token boolean">false</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">if</span> <span class="token punctuation">(</span><span class="token function">isLatin1</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">if</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>val<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">&</span> <span class="token number">0xff</span><span class="token punctuation">)</span> <span class="token operator">!=</span> cs<span class="token punctuation">.</span><span class="token function">charAt</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

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

<span class="token keyword">if</span> <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">contentEquals</span><span class="token punctuation">(</span>val<span class="token punctuation">,</span> cs<span class="token punctuation">,</span> n<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

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

<span class="token keyword">return</span> <span class="token boolean">true</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 class="line-number"></div></div></div><p>从源码上可以看得出，如果 cs 是 StringBuffer，该方法还会进行同步，非常的智能化；如果是 String 的话，其实调用的还是 <code>equals()</code> 方法。当然了，这也就意味着使用该方法进行比较的时候，多出来了很多步骤，性能上有些损失。</p><p>“是的，总体上感觉还是 <code>Objects.equals()</code> 比较舒服。”三妹的眼睛是雪亮的，发现了这个方法的优点。</p><hr><p>最近整理了一份牛逼的学习资料，包括但不限于Java基础部分（JVM、Java集合框架、多线程），还囊括了 <strong>数据库、计算机网络、算法与数据结构、设计模式、框架类Spring、Netty、微服务（Dubbo，消息队列）网关</strong> 等等等等……详情戳：<a href="https://tobebetterjavaer.com/pdf/programmer-111.html" target="_blank" rel="noopener noreferrer">可以说是2022年全网最全的学习和找工作的PDF资源了<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path><polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg><span class="external-link-icon-sr-only">open in new window</span></span></a></p><p>微信搜 <strong>沉默王二</strong> 或扫描下方二维码关注二哥的原创公众号沉默王二，回复 <strong>111</strong> 即可免费领取。</p><p><img src="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/gongzhonghao.png" alt="" loading="lazy"></p></div><footer class="page-meta"><div class="meta-item edit-link"><a href="https://github.com/itwanger/toBeBetterJavaer/edit/master/docs/string/equals.md" rel="noopener noreferrer" target="_blank" aria-label="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>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></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="/string/intern.html" class="nav-link prev" aria-label="深入解析String.intern()方法"><div class="hint"><span class="arrow left"></span>上一页</div><div class="link">深入解析String.intern()方法</div></a><a href="/string/join.html" class="nav-link next" aria-label="Java字符串拼接"><div class="hint">下一页<span class="arrow right"></span></div><div class="link">Java字符串拼接</div></a></nav><div class="giscus-wrapper input-top" style="display:block;"><div style="text-align:center">Loading...</div></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><!--]--& 30F2 gt;</div>

</body>

</html>

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

FilesExpand file tree

equals.html

Latest commit

History

equals.html

File metadata and controls