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right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.3 数组&字符串</span><span class="arrow right"></span></button><!----></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable active"><!----><span class="title">2.4 面向对象编程</span><span class="arrow down"></span></button><ul class="sidebar-links"><li><!--[--><a href="/oo/object-class.html" class="nav-link sidebar-link sidebar-page" aria-label="对象和类"><!---->对象和类<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/var.html" class="nav-link sidebar-link sidebar-page" aria-label="Java变量"><!---->Java变量<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a aria-current="page" href="/oo/method.html" class="router-link-active router-link-exact-active nav-link active sidebar-link sidebar-page active" aria-label="方法"><!---->方法<!----></a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a aria-current="page" href="/oo/method.html#_01、java-中的方法是什么" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="01、Java 中的方法是什么？"><!---->01、Java 中的方法是什么？<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/oo/method.html#_02、如何声明方法" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="02、如何声明方法？"><!---->02、如何声明方法？<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/oo/method.html#_02、方法有哪几种" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="02、方法有哪几种？"><!---->02、方法有哪几种？<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/oo/method.html#_03、什么是实例方法" class="router-link-active 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sidebar-page" aria-label="final"><!---->final<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/oo/instanceof.html" class="nav-link sidebar-link sidebar-page" aria-label="instanceof"><!---->instanceof<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/immutable.html" class="nav-link sidebar-link sidebar-page" aria-label="不可变对象"><!---->不可变对象<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/varables.html" class="nav-link sidebar-link sidebar-page" aria-label="可变参数"><!---->可变参数<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/generic.html" class="nav-link sidebar-link sidebar-page" aria-label="泛型"><!---->泛型<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/annotation.html" class="nav-link sidebar-link sidebar-page" aria-label="注解"><!---->注解<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/enum.html" class="nav-link sidebar-link sidebar-page" aria-label="枚举"><!---->枚举<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a href="/basic-extra-meal/fanshe.html" class="nav-link sidebar-link sidebar-page" aria-label="反射"><!---->反射<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li></ul></section><!--]--></li><li><!--[--><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.5 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><!---->Java方法</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 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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 tag4 clickable" role="navigation">Java</li></ul><meta property="keywords" content="Java"></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 6 分钟</span><meta property="timeRequired" content="PT6M"></span></div><hr></div><div class="toc-place-holder"><aside id="toc"><div class="toc-header">此页内容</div><div class="toc-wrapper"><ul class="toc-list"><!--[--><li class="toc-item"><a aria-current="page" href="/oo/method.html#_01、java-中的方法是什么" class="router-link-active router-link-exact-active toc-link level3">01、Java 中的方法是什么？</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/oo/method.html#_02、如何声明方法" class="router-link-active router-link-exact-active toc-link level3">02、如何声明方法？</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/oo/method.html#_02、方法有哪几种" class="router-link-active router-link-exact-active toc-link level3">02、方法有哪几种？</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/oo/method.html#_03、什么是实例方法" class="router-link-active router-link-exact-active toc-link level3">03、什么是实例方法？</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/oo/method.html#_04、什么是抽象方法" class="router-link-active router-link-exact-active toc-link level3">04、什么是抽象方法？</a></li><!----><!--]--></ul></div></aside></div><!----><div class="theme-hope-content"><h1 id="java方法" tabindex="-1"><a class="header-anchor" href="#java方法" aria-hidden="true">#</a> Java方法</h1><p>“二哥，<a href="https://mp.weixin.qq.com/s/UExby8GP3kSacCXliQw8pQ" target="_blank" rel="noopener noreferrer">上一节<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>学了对象和类，这一节我们学什么呢？”三妹满是期待的问我。</p><p>“这一节我们来了解一下 Java 中的方法——什么是方法？如何声明方法？方法有哪几种？什么是实例方法？什么是抽象方法？”我笑着对三妹说，“我开始了啊，你不要闪啊。”</p><h3 id="_01、java-中的方法是什么" tabindex="-1"><a class="header-anchor" href="#_01、java-中的方法是什么" aria-hidden="true">#</a> 01、Java 中的方法是什么？</h3><p>方法用来实现代码的可重用性，我们编写一次方法，并多次使用它。通过增加或者删除方法中的一部分代码，就可以提高整体代码的可读性。</p><p>只有方法被调用时，它才会执行。Java 中最有名的方法当属 <code>main()</code> 方法，点击下面的链接可以阅读更多关于 <code>main()</code> 方法的知识点。</p><blockquote><p><a href="https://mp.weixin.qq.com/s/191I_2CVOxVuyfLVtb4jhg" target="_blank" rel="noopener noreferrer">零基础学 Java 第 4 讲：Hello World<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></blockquote><h3 id="_02、如何声明方法" tabindex="-1"><a class="header-anchor" href="#_02、如何声明方法" aria-hidden="true">#</a> 02、如何声明方法？</h3><p>方法的声明反映了方法的一些信息，比如说可见性、返回类型、方法名和参数。如下图所示。</p><p><img src="http://cdn.tobebetterjavaer.com/tobebetterjavaer/images/object-class/17-01.png" alt=""></p><p><strong>访问权限</strong>：它指定了方法的可见性。Java 提供了四种访问权限修饰符：</p><ul><li>public：该方法可以被所有类访问。</li><li>private：该方法只能在定义它的类中访问。</li><li>protected：该方法可以被同一个包中的类，或者不同包中的子类访问。</li><li>default：该方法如果没有使用任何访问权限修饰符，Java 默认它使用 default 修饰符，该方法只能被同一个包中类可见。</li></ul><p><strong>返回类型</strong>：方法返回的数据类型，可以是基本数据类型、对象和集合，如果不需要返回数据，则使用 void 关键字。</p><p><strong>方法名</strong>：方法名最好反应出方法的功能，比如，我们要创建一个将两个数字相减的方法，那么方法名最好是 subtract。</p><p>方法名最好是一个动词，并且以小写字母开头。如果方法名包含两个以上单词，那么第一个单词最好是动词，然后是形容词或者名词，并且要以驼峰式的命名方式命名。比如：</p><ul><li>一个单词的方法名：<code>sum()</code></li><li>多个单词的方法名：<code>stringComparision()</code></li></ul><p>一个方法可能与同一个类中的另外一个方法同名，这被称为方法重载。</p><p><strong>参数</strong>：参数被放在一个圆括号内，如果有多个参数，可以使用逗号隔开。参数包含两个部分，参数类型和参数名。如果方法没有参数，圆括号是空的。</p><p><strong>方法签名</strong>：每一个方法都有一个签名，包括方法名和参数。</p><p><strong>方法体</strong>：方法体放在一对花括号内，把一些代码放在一起，用来执行特定的任务。</p><h3 id="_02、方法有哪几种" tabindex="-1"><a class="header-anchor" href="#_02、方法有哪几种" aria-hidden="true">#</a> 02、方法有哪几种？</h3><p>方法可以分为两种，一种叫预先定义方法，一种叫用户自定义方法。</p><p><strong>1）预先定义方法</strong></p><p>Java 提供了大量预先定义好的方法供我们调用，也称为标准类库方法，或者内置方法。比如说 String 类的 <code>length()</code>、<code>equals()</code>、<code>compare()</code> 方法，以及我们在初学 Java 阶段最常用的 <code>println()</code> 方法，用来在控制台打印信息。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 微信搜「沉默王二」，回复关键字 PDF
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">PredefinedMethodDemo</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 string">"沉默王二，一枚有趣的程序员"</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>在上面的代码中，我们使用了两个预先定义的方法，<code>main()</code> 方法是程序运行的入口，<code>println()</code> 方法是 <code>PrintStream</code> 类的一个方法。这些方法已经提前定义好了，所以我们可以直接使用它们。</p><p>我们可以通过集成开发工具查看预先定义方法的方法签名，当我们把鼠标停留在 <code>println()</code> 方法上面时，就会显示下图中的内容：</p><p><img src="http://cdn.tobebetterjavaer.com/tobebetterjavaer/images/object-class/17-02.png" alt=""></p><p><code>println()</code> 方法的访问权限修饰符是 public，返回类型为 void，方法名为 println，参数为 <code>String x</code>，以及 Javadoc（方法是干嘛的）。</p><p>预先定义方法让编程变得简单了起来，我们只需要在实现某些功能的时候直接调用这些方法即可，不需要重新编写。</p><p><strong>2）用户自定义方法</strong></p><p>当预先定义方法无法满足我们的要求时，就需要自定义一些方法，比如说，我们来定义这样一个方法，用来检查数字是偶数还是奇数。</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">static</span> <span class="token keyword">void</span> <span class="token function">findEvenOdd</span><span class="token punctuation">(</span><span class="token keyword">int</span> num<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>num <span class="token operator">%</span> <span class="token number">2</span> <span class="token operator">==</span> <span class="token number">0</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>num <span class="token operator">+</span> <span class="token string">" 是偶数"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">else</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>num <span class="token operator">+</span> <span class="token string">" 是奇数"</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></div><p>方法名叫做 <code>findEvenOdd</code>，访问权限修饰符是 public，并且是静态的（static），返回类型是 void，参数有一个整型（int）的 num。方法体中有一个 if else 语句，如果 num 可以被 2 整除，那么就打印这个数字是偶数，否则就打印这个数字是奇数。</p><p>方法被定义好后，如何被调用呢？</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 微信搜「沉默王二」，回复关键字 PDF
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">EvenOddDemo</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 function">findEvenOdd</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">findEvenOdd</span><span class="token punctuation">(</span><span class="token number">11</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">findEvenOdd</span><span class="token punctuation">(</span><span class="token keyword">int</span> num<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>num <span class="token operator">%</span> <span class="token number">2</span> <span class="token operator">==</span> <span class="token number">0</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>num <span class="token operator">+</span> <span class="token string">" 是偶数"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">else</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>num <span class="token operator">+</span> <span class="token string">" 是奇数"</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></div><p><code>main()</code> 方法是程序的入口，并且是静态的，那么就可以直接调用同样是静态方法的 <code>findEvenOdd()</code>。</p><p>当一个方法被 static 关键字修饰时，它就是一个静态方法。换句话说，静态方法是属于类的，不属于类实例的（不需要通过 new 关键字创建对象来调用，直接通过类名就可以调用）。</p><h3 id="_03、什么是实例方法" tabindex="-1"><a class="header-anchor" href="#_03、什么是实例方法" aria-hidden="true">#</a> 03、什么是实例方法？</h3><p>没有使用 static 关键字修饰，但在类中声明的方法被称为实例方法，在调用实例方法之前，必须创建类的对象。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 微信搜「沉默王二」，回复关键字 PDF
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">InstanceMethodExample</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">InstanceMethodExample</span> instanceMethodExample <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">InstanceMethodExample</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>instanceMethodExample<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">)</span><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">add</span><span class="token punctuation">(</span><span class="token keyword">int</span> a<span class="token punctuation">,</span> <span class="token keyword">int</span> b<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> a <span class="token operator">+</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 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>add()</code> 方法是一个实例方法，需要创建 InstanceMethodExample 对象来访问。</p><p>实例方法有两种特殊类型：</p><ul><li>getter 方法</li><li>setter 方法</li></ul><p>getter 方法用来获取私有变量（private 修饰的字段）的值，setter 方法用来设置私有变量的值。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 沉默王二，一枚有趣的程序员
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Person</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span> <span class="token class-name">String</span> name<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> age<span class="token punctuation">;</span>
<span class="token keyword">private</span> <span class="token keyword">int</span> sex<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 keyword">public</span> <span class="token keyword">void</span> <span class="token function">setName</span><span class="token punctuation">(</span><span class="token class-name">String</span> name<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 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 keyword">void</span> <span class="token function">setAge</span><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>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">getSex</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> sex<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">setSex</span><span class="token punctuation">(</span><span class="token keyword">int</span> sex<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>sex <span class="token operator">=</span> sex<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>getter 方法以 get 开头，setter 方法以 set 开头。</p><h3 id="_04、什么是抽象方法" tabindex="-1"><a class="header-anchor" href="#_04、什么是抽象方法" aria-hidden="true">#</a> 04、什么是抽象方法？</h3><p>没有方法体的方法被称为抽象方法，它总是在抽象类中声明。这意味着如果类有抽象方法的话，这个类就必须是抽象的。可以使用 atstract 关键字创建抽象方法和抽象类。</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 微信搜「沉默王二」，回复关键字 PDF
*/</span>
<span class="token keyword">abstract</span> <span class="token keyword">class</span> <span class="token class-name">AbstractDemo</span> <span class="token punctuation">{</span>
<span class="token keyword">abstract</span> <span class="token keyword">void</span> <span class="token function">display</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></div><p>当一个类继承了抽象类后，就必须重写抽象方法：</p><div class="language-java ext-java line-numbers-mode"><pre class="language-java"><code><span class="token doc-comment comment">/**
* <span class="token keyword">@author</span> 微信搜「沉默王二」，回复关键字 PDF
*/</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">MyAbstractDemo</span> <span class="token keyword">extends</span> <span class="token class-name">AbstractDemo</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Override</span>
<span class="token keyword">void</span> <span class="token function">display</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">"重写了抽象方法"</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">MyAbstractDemo</span> myAbstractDemo <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyAbstractDemo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
myAbstractDemo<span class="token punctuation">.</span><span class="token function">display</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></div><p>输出结果如下所示：</p><div class="language-text ext-text line-numbers-mode"><pre class="language-text"><code>重写了抽象方法
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><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/oo/method.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">2022/5/14 上午7:14:28</span></div><div class="meta-item contributors"><span class="label">贡献者: </span><!--[--><!--[--><span class="contributor" title="email: [email protected]">itwanger</span>,<!--]--><!--[--><span class="contributor" title="email: [email protected]">沉默王二</span><!--]--><!--]--></div></footer><nav class="page-nav"><a href="/oo/var.html" class="nav-link prev" aria-label="Java变量"><div class="hint"><span class="arrow left"></span>上一页</div><div class="link"><!---->Java变量</div></a><a href="/oo/construct.html" class="nav-link next" aria-label="构造方法"><div class="hint">下一页<span class="arrow right"></span></div><div class="link">构造方法<!----></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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