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    <entry>
      <title>比较器</title>
      <link href="/2020/04/11/bi-jiao-qi/"/>
      <url>/2020/04/11/bi-jiao-qi/</url>
      
        <content type="html"><![CDATA[<h1 id="Java中常见的比较器的实现方法"><a href="#Java中常见的比较器的实现方法" class="headerlink" title="Java中常见的比较器的实现方法"></a><a href="https://www.cnblogs.com/ldy-blogs/p/8488138.html" target="_blank" rel="noopener">Java中常见的比较器的实现方法</a></h1><p>在Java中经常会涉及到对象数组的排序问题，那么就涉及到对象之间的比较问题。</p><p>通常对象之间的比较可以从两个方面去看：</p><p>第一个方面：对象的地址是否一样，也就是是否引用自同一个对象。这种方式可以直接使用“==“来完成。</p><p>第二个方面：以对象的某一个属性的角度去比较。</p><p>对于JDK8而言，有三种实现对象比较的方法：</p><p>1、覆写Object类的equals（）方法；</p><p>2、继承Comparable接口，并实现compareTo（）方法；</p><p>3、定义一个单独的对象比较器，继承自Comparator接口，实现compare（）方法。</p><p>由于使用的排序方式的不同，具体选择哪种方法来实现对象的比较也会有所不同。</p><p>第一种方法比较便于理解，复写equals()方法一般用于自己实现的对象数组排序，而对于在应用Java内置的排序算法时，使用后两种方式都是可以实现的。</p><p>先来看一下第二种方式，这种方式就是让自己编写的类继承Comparable接口，并实现接口的compareTo()方法，这种情况下，在使用java.util.Arrays.sort()方法时不用指定具体的比较器，sort()方法会使用对象自己的比较函数对对象进行排序。具体实例代码如下：</p><pre class=" language-java"><code class="language-java"><span class="token keyword">import</span> java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>Arrays<span class="token punctuation">;</span><span class="token keyword">class</span> <span class="token class-name">BookCook</span> <span class="token keyword">implements</span> <span class="token class-name">Comparable</span><span class="token operator">&lt;</span>BookCook<span class="token operator">></span><span class="token punctuation">{</span>    <span class="token keyword">private</span> String title<span class="token punctuation">;</span>    <span class="token keyword">private</span> <span class="token keyword">double</span> price<span class="token punctuation">;</span>    <span class="token keyword">public</span> <span class="token function">BookCook</span><span class="token punctuation">(</span>String title<span class="token punctuation">,</span><span class="token keyword">double</span> price<span class="token punctuation">)</span><span class="token punctuation">{</span>        <span class="token keyword">this</span><span class="token punctuation">.</span>title <span class="token operator">=</span> title<span class="token punctuation">;</span>        <span class="token keyword">this</span><span class="token punctuation">.</span>price <span class="token operator">=</span> price<span class="token punctuation">;</span>    <span class="token punctuation">}</span>    <span class="token annotation punctuation">@Override</span>    <span class="token keyword">public</span> String <span class="token function">toString</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 string">"书名："</span><span class="token operator">+</span><span class="token keyword">this</span><span class="token punctuation">.</span>title<span class="token operator">+</span><span class="token string">",价格："</span><span class="token operator">+</span><span class="token keyword">this</span><span class="token punctuation">.</span>price<span class="token punctuation">;</span>    <span class="token punctuation">}</span>    <span class="token annotation punctuation">@Override</span>    <span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">compareTo</span><span class="token punctuation">(</span>BookCook o<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 punctuation">.</span>price <span class="token operator">></span> o<span class="token punctuation">.</span>price<span class="token punctuation">)</span><span class="token punctuation">{</span>            <span class="token keyword">return</span> <span class="token number">1</span><span class="token punctuation">;</span>        <span class="token punctuation">}</span><span class="token keyword">else</span> <span class="token keyword">if</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span>price <span class="token operator">&lt;</span> o<span class="token punctuation">.</span>price<span class="token punctuation">)</span><span class="token punctuation">{</span>            <span class="token keyword">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>        <span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>            <span class="token keyword">return</span> <span class="token number">0</span><span class="token punctuation">;</span>        <span class="token punctuation">}</span>    <span class="token punctuation">}</span><span class="token punctuation">}</span></code></pre><p>从JDK1.8开始出现了Comparator接口，它的出现解决了当需要在已经开发好的代码基础上完善对象的比较功能时不想更改之前的代码的问题。这种情况，我们需要单独定义一个对象比较器，继承Comparator接口。具体实现代码如下：</p><pre class=" language-java"><code class="language-java"><span class="token keyword">class</span> <span class="token class-name">Student</span> <span class="token punctuation">{</span>    <span class="token keyword">private</span> String name<span class="token punctuation">;</span>    <span class="token keyword">private</span> <span class="token keyword">double</span> score<span class="token punctuation">;</span>    <span class="token keyword">public</span> <span class="token function">Student</span><span class="token punctuation">(</span>String name<span class="token punctuation">,</span><span class="token keyword">double</span> score<span class="token punctuation">)</span><span class="token punctuation">{</span>        <span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>        <span class="token keyword">this</span><span class="token punctuation">.</span>score <span class="token operator">=</span> score<span class="token punctuation">;</span>    <span class="token punctuation">}</span>    <span class="token keyword">public</span> <span class="token keyword">double</span> <span class="token function">getScore</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 keyword">this</span><span class="token punctuation">.</span>score<span class="token punctuation">;</span>    <span class="token punctuation">}</span>    <span class="token annotation punctuation">@Override</span>    <span class="token keyword">public</span> String <span class="token function">toString</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 string">"姓名:"</span><span class="token operator">+</span><span class="token keyword">this</span><span class="token punctuation">.</span>name<span class="token operator">+</span><span class="token string">",分数:"</span><span class="token operator">+</span><span class="token keyword">this</span><span class="token punctuation">.</span>score<span class="token punctuation">;</span>    <span class="token punctuation">}</span><span class="token punctuation">}</span><span class="token keyword">class</span> <span class="token class-name">StudentComparator</span> <span class="token keyword">implements</span> <span class="token class-name">Comparator</span><span class="token operator">&lt;</span>Student<span class="token operator">></span> <span class="token punctuation">{</span>    <span class="token annotation punctuation">@Override</span>    <span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">compare</span><span class="token punctuation">(</span>Student o1<span class="token punctuation">,</span>Student o2<span class="token punctuation">)</span> <span class="token punctuation">{</span>        <span class="token keyword">if</span><span class="token punctuation">(</span>o1<span class="token punctuation">.</span><span class="token function">getScore</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> o2<span class="token punctuation">.</span><span class="token function">getScore</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 number">1</span><span class="token punctuation">;</span>        <span class="token punctuation">}</span><span class="token keyword">else</span> <span class="token keyword">if</span><span class="token punctuation">(</span>o1<span class="token punctuation">.</span><span class="token function">getScore</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&lt;</span> o2<span class="token punctuation">.</span><span class="token function">getScore</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 operator">-</span><span class="token number">1</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 keyword">return</span> <span class="token number">0</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">class</span> <span class="token class-name">TestComparator</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>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>        Student<span class="token punctuation">[</span><span class="token punctuation">]</span> sts <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Student</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">{</span>                <span class="token keyword">new</span> <span class="token class-name">Student</span><span class="token punctuation">(</span><span class="token string">"小戴"</span><span class="token punctuation">,</span><span class="token number">60</span><span class="token punctuation">)</span><span class="token punctuation">,</span>                <span class="token keyword">new</span> <span class="token class-name">Student</span><span class="token punctuation">(</span><span class="token string">"小王"</span><span class="token punctuation">,</span><span class="token number">90</span><span class="token punctuation">)</span><span class="token punctuation">,</span>                <span class="token keyword">new</span> <span class="token class-name">Student</span><span class="token punctuation">(</span><span class="token string">"老王"</span><span class="token punctuation">,</span><span class="token number">80</span><span class="token punctuation">)</span><span class="token punctuation">,</span>                <span class="token keyword">new</span> <span class="token class-name">Student</span><span class="token punctuation">(</span><span class="token string">"小萱"</span><span class="token punctuation">,</span><span class="token number">95</span><span class="token punctuation">)</span>        <span class="token punctuation">}</span><span class="token punctuation">;</span>        java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>Arrays<span class="token punctuation">.</span><span class="token function">sort</span><span class="token punctuation">(</span>sts<span class="token punctuation">,</span> <span class="token keyword">new</span> <span class="token class-name">StudentComparator</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>Arrays<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span>sts<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><script>        document.querySelectorAll('.github-emoji')          .forEach(el => {            if (!el.dataset.src) { return; }            const img = document.createElement('img');            img.style = 'display:none !important;';            img.src = el.dataset.src;            img.addEventListener('error', () => {              img.remove();              el.style.color = 'inherit';              el.style.backgroundImage = 'none';           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    <entry>
      <title>Hello World</title>
      <link href="/2020/04/08/hello-world/"/>
      <url>/2020/04/08/hello-world/</url>
      
        <content type="html"><![CDATA[<p>Welcome to <a href="https://hexo.io/" target="_blank" rel="noopener">Hexo</a>! This is your very first post. Check <a href="https://hexo.io/docs/" target="_blank" rel="noopener">documentation</a> for more info. If you get any problems when using Hexo, you can find the answer in <a href="https://hexo.io/docs/troubleshooting.html" target="_blank" rel="noopener">troubleshooting</a> or you can ask me on <a href="https://github.com/hexojs/hexo/issues" target="_blank" rel="noopener">GitHub</a>.</p><h2 id="Quick-Start"><a href="#Quick-Start" class="headerlink" title="Quick Start"></a>Quick Start</h2><h3 id="Create-a-new-post"><a href="#Create-a-new-post" class="headerlink" title="Create a new post"></a>Create a new post</h3><pre class=" language-bash"><code class="language-bash">$ hexo new <span class="token string">"My New Post"</span></code></pre><p>More info: <a href="https://hexo.io/docs/writing.html" target="_blank" rel="noopener">Writing</a></p><h3 id="Run-server"><a href="#Run-server" class="headerlink" title="Run server"></a>Run server</h3><pre class=" language-bash"><code class="language-bash">$ hexo server</code></pre><p>More info: <a href="https://hexo.io/docs/server.html" target="_blank" rel="noopener">Server</a></p><h3 id="Generate-static-files"><a href="#Generate-static-files" class="headerlink" title="Generate static files"></a>Generate static files</h3><pre class=" language-bash"><code class="language-bash">$ hexo generate</code></pre><p>More info: <a href="https://hexo.io/docs/generating.html" target="_blank" rel="noopener">Generating</a></p><h3 id="Deploy-to-remote-sites"><a href="#Deploy-to-remote-sites" class="headerlink" title="Deploy to remote sites"></a>Deploy to remote sites</h3><pre class=" language-bash"><code class="language-bash">$ hexo deploy</code></pre><p>More info: <a href="https://hexo.io/docs/one-command-deployment.html" target="_blank" rel="noopener">Deployment</a></p><script>        document.querySelectorAll('.github-emoji')          .forEach(el => {            if (!el.dataset.src) { return; }            const img = document.createElement('img');            img.style = 'display:none !important;';            img.src = el.dataset.src;            img.addEventListener('error', () => {              img.remove();              el.style.color = 'inherit';              el.style.backgroundImage = 'none';              el.style.background = 'none';            });            img.addEventListener('load', () => {              img.remove();            });            document.body.appendChild(img);          });      </script>]]></content>
      
      
      
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