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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Hexo</title>
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
<meta property="og:type" content="website">
<meta property="og:title" content="Hexo">
<meta property="og:url" content="http://yoursite.com/index.html">
<meta property="og:site_name" content="Hexo">
<meta name="twitter:card" content="summary">
<meta name="twitter:title" content="Hexo">
<link rel="alternate" href="/atom.xml" title="Hexo" type="application/atom+xml">
<link rel="icon" href="/favicon.png">
<link href="//fonts.googleapis.com/css?family=Source+Code+Pro" rel="stylesheet" type="text/css">
<link rel="stylesheet" href="/css/style.css">
</head>
<body>
<div id="container">
<div id="wrap">
<header id="header">
<div id="banner"></div>
<div id="header-outer" class="outer">
<div id="header-title" class="inner">
<h1 id="logo-wrap">
<a href="/" id="logo">Hexo</a>
</h1>
</div>
<div id="header-inner" class="inner">
<nav id="main-nav">
<a id="main-nav-toggle" class="nav-icon"></a>
<a class="main-nav-link" href="/">Home</a>
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</nav>
<nav id="sub-nav">
<a id="nav-rss-link" class="nav-icon" href="/atom.xml" title="RSS Feed"></a>
<a id="nav-search-btn" class="nav-icon" title="Search"></a>
</nav>
<div id="search-form-wrap">
<form action="//google.com/search" method="get" accept-charset="UTF-8" class="search-form"><input type="search" name="q" results="0" class="search-form-input" placeholder="Search"><button type="submit" class="search-form-submit"></button><input type="hidden" name="sitesearch" value="http://yoursite.com"></form>
</div>
</div>
</div>
</header>
<div class="outer">
<section id="main">
<article id="post-hexo-tips" class="article article-type-post" itemscope itemprop="blogPost">
<div class="article-meta">
<a href="/2017/09/04/hexo-tips/" class="article-date">
<time datetime="2017-09-04T09:31:56.000Z" itemprop="datePublished">2017-09-04</time>
</a>
</div>
<div class="article-inner">
<header class="article-header">
<h1 itemprop="name">
<a class="article-title" href="/2017/09/04/hexo-tips/">从 CSDN 博客迁移到个人 Hexo 站点的一点坑</a>
</h1>
</header>
<div class="article-entry" itemprop="articleBody">
<h1 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h1><p>最近把 原来 CSDN 博客迁移到了个人博客。</p>
<p>原先 CSDN 博客：<a href="http://blog.csdn.net/never_cxb" target="_blank" rel="external">http://blog.csdn.net/never_cxb</a></p>
<p>独立个人博客：<a href="http://www.alijava.com/" target="_blank" rel="external">http://www.alijava.com/</a></p>
<h2 id="配置信息"><a href="#配置信息" class="headerlink" title="配置信息"></a>配置信息</h2><ul>
<li>由 Hexo 强力驱动 </li>
<li>主题 - NexT.Mist</li>
<li>图片存储于七牛云 </li>
<li>服务器 nginx</li>
<li>部署于阿里云</li>
<li>已备案</li>
<li>评论： 多说</li>
<li>统计阅读次数：LeanCloud</li>
<li>搜索引擎优化：百度站长</li>
</ul>
<p>如果您还没有注册七牛，可以通过我的邀请链接注册 <a href="https://portal.qiniu.com/signup?code=3lpzf1unpyr0y" target="_blank" rel="external">https://portal.qiniu.com/signup?code=3lpzf1unpyr0y</a>，可以享受特有优惠以及免费空间。</p>
<h2 id="nginx-常用命令"><a href="#nginx-常用命令" class="headerlink" title="nginx 常用命令"></a>nginx 常用命令</h2><ul>
<li><code>sudo service nginx restart</code> 重启服务器nginx</li>
</ul>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line">sudo service nginx start</div><div class="line">sudo service nginx stop</div><div class="line">sudo service nginx restart</div></pre></td></tr></table></figure>
<p>安装 <code>next</code> 官网教程配置<strong>腾讯404 页面</strong>，发现总是无法显示</p>
<p>后来发现是因为<code>nginx</code>的问题，需要配置 <code>404</code>路径，</p>
<p>设 404 为 <code>hexo</code> 的 <code>public</code> 目录 <code>/usr/local/hexo/blog/public</code></p>
<p>加上 <code>fastcgi_intercept_errors on</code>，现在就可以正常访问了</p>
<p><a href="http://www.alijava.com/404.html" target="_blank" rel="external">http://www.alijava.com/404.html</a></p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div></pre></td><td class="code"><pre><div class="line">error_page 404 /404.html;</div><div class="line"></div><div class="line">location = /404.html {</div><div class="line"> root /usr/local/hexo/blog/public;</div><div class="line">}</div><div class="line"></div><div class="line">fastcgi_intercept_errors on;</div></pre></td></tr></table></figure>
<h2 id="Todo-List"><a href="#Todo-List" class="headerlink" title="Todo List"></a>Todo List</h2><ul>
<li>git 版本控制，备份</li>
<li>推广，搜索引擎优化</li>
</ul>
<h2 id="Hexo-常用命令"><a href="#Hexo-常用命令" class="headerlink" title="Hexo 常用命令"></a>Hexo 常用命令</h2><ul>
<li><p><code>hexo new "java-basics" 或者 hexo n "java-basics"</code></p>
</li>
<li><p><code>hexo generate 或者 hexo g</code> 生成静态文件至<code>public</code>目录</p>
</li>
<li><p><code>hexo server 或者 hexo s</code> 启动服务预览</p>
</li>
<li><p><code>hexo s -p 5000</code> 将默认端口<code>4000</code>修改为<code>5000</code></p>
</li>
</ul>
<h2 id="保持ssh连接不断线"><a href="#保持ssh连接不断线" class="headerlink" title="保持ssh连接不断线"></a>保持ssh连接不断线</h2><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">ssh -o ServerAliveInterval=60 root@115.**.**.**</div></pre></td></tr></table></figure>
<p>意思是每60秒发送一个信号重连</p>
<h1 id="搜索引擎优化"><a href="#搜索引擎优化" class="headerlink" title="搜索引擎优化"></a>搜索引擎优化</h1><p>主要是通过百度站长平台，希望能够提升博客在搜索引擎的收录数量及排序位置</p>
<h2 id="主动推送-实时"><a href="#主动推送-实时" class="headerlink" title="主动推送(实时)"></a>主动推送(实时)</h2><p>官方文档这么说：</p>
<p>将要提交的链接按照每行一条的格式写入一个文本文件中，命名此文件为urls.txt，<br>然后进入该文件所在目录，执行如下命令：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">curl -H 'Content-Type:text/plain' --data-binary @urls.txt "http://data.zz.baidu.com/urls?site=www.alijava.com&token=2FncXBwaZ5iVh5oT"</div></pre></td></tr></table></figure></p>
<p>为了方便提交，写了一个脚本，方便 <code>curl</code> 提交链接。</p>
<p>（1）<code>ls source/_posts | grep ".md$"</code> ，输出<code>source/_posts</code>以<code>.md</code>结尾的文件名<br>（2）笔者的文章 <code>url</code> 为 <code>http://www.alijava.com/</code> + 文件名，利用 <code>sed -e 's/\.md$//'</code>去掉后缀 <code>.md</code><br>（3）<code>sed -e 's/^/http:\/\/www.alijava.com\//'</code>加上网站前缀</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">ls source/_posts | grep ".md$" | sed -e 's/\.md$//' -e 's/^/http:\/\/www.alijava.com\//' > urls.txt</div><div class="line">echo `curl -H 'Content-Type:text/plain' --data-binary @urls.txt "http://data.zz.baidu.com/urls?site=www.alijava.com&token=你的token"`</div></pre></td></tr></table></figure>
<h2 id="sitemap"><a href="#sitemap" class="headerlink" title="sitemap"></a>sitemap</h2><p>注意在你的<strong>hexo 博客目录</strong>，执行下面命令</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">npm install hexo-generator-sitemap --save</div><div class="line">npm install hexo-generator-baidu-sitemap --save</div></pre></td></tr></table></figure>
<p><strong>站点配置文件</strong> 增加<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div></pre></td><td class="code"><pre><div class="line">sitemap:</div><div class="line"> path: sitemap.xml</div><div class="line">baidusitemap:</div><div class="line"> path: baidusitemap.xml</div></pre></td></tr></table></figure></p>
<p>然后重新编译并部署</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">hexo clean</div><div class="line">hexo g</div></pre></td></tr></table></figure>
<p>站点地图就可以通过下面链接访问了</p>
<ul>
<li><a href="http://alijava.com/sitemap.xml" target="_blank" rel="external">http://alijava.com/sitemap.xml</a></li>
<li><a href="http://alijava.com/baidusitemap.xml" target="_blank" rel="external">http://alijava.com/baidusitemap.xml</a></li>
</ul>
<h2 id="sitemap-的坑"><a href="#sitemap-的坑" class="headerlink" title="sitemap 的坑"></a>sitemap 的坑</h2><p>把生成的<code>sitemap</code>提交百度站长之家后，发现状态为<code>主域校验失败</code></p>
<p>原因是生成的 <code>sitemap.xml</code> 里面的是 <code>http://yoursite.com/common-tools/</code>，前缀不是网站真实网址</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div></pre></td><td class="code"><pre><div class="line"><span class="tag"><<span class="name">url</span>></span></div><div class="line"><span class="tag"><<span class="name">loc</span>></span>http://yoursite.com/common-tools/<span class="tag"></<span class="name">loc</span>></span></div><div class="line"><span class="tag"><<span class="name">lastmod</span>></span>2016-09-03T08:28:25.843Z<span class="tag"></<span class="name">lastmod</span>></span></div><div class="line"><span class="tag"></<span class="name">url</span>></span></div></pre></td></tr></table></figure>
<p>目前的方法是手动修改 <code>sitemap.xml</code> 和<code>baidusitemap.xml</code>，但是每次<code>hexo g</code>部署之后都需要修改，<strong>不知道有没有其他方法</strong>？</p>
<p>可以利用 <code>vim</code> 修改文件</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">:%s/yoursite/www.alijava/g</div></pre></td></tr></table></figure>
<p>将<code>yoursite.com</code>替换为<code>www.alijava.com</code>，<code>g</code>表示替换所有</p>
<h2 id="参考文章"><a href="#参考文章" class="headerlink" title="参考文章"></a>参考文章</h2><ul>
<li><a href="http://oakland.github.io/2016/05/02/hexo-%E5%A6%82%E4%BD%95%E7%94%9F%E6%88%90%E4%B8%80%E7%AF%87%E6%96%B0%E7%9A%84post/" target="_blank" rel="external">http://oakland.github.io/2016/05/02/hexo-%E5%A6%82%E4%BD%95%E7%94%9F%E6%88%90%E4%B8%80%E7%AF%87%E6%96%B0%E7%9A%84post/</a></li>
</ul>
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<a href="/2017/02/09/hello-world/" class="article-date">
<time datetime="2017-02-09T12:16:16.000Z" itemprop="datePublished">2017-02-09</time>
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<h1 itemprop="name">
<a class="article-title" href="/2017/02/09/hello-world/">Hello World</a>
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<p>Welcome to <a href="https://hexo.io/" target="_blank" rel="external">Hexo</a>! This is your very first post. Check <a href="https://hexo.io/docs/" target="_blank" rel="external">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="external">troubleshooting</a> or you can ask me on <a href="https://github.com/hexojs/hexo/issues" target="_blank" rel="external">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><figure class="highlight bash"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">$ hexo new <span class="string">"My New Post"</span></div></pre></td></tr></table></figure>
<p>More info: <a href="https://hexo.io/docs/writing.html" target="_blank" rel="external">Writing</a></p>
<h3 id="Run-server"><a href="#Run-server" class="headerlink" title="Run server"></a>Run server</h3><figure class="highlight bash"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">$ hexo server</div></pre></td></tr></table></figure>
<p>More info: <a href="https://hexo.io/docs/server.html" target="_blank" rel="external">Server</a></p>
<h3 id="Generate-static-files"><a href="#Generate-static-files" class="headerlink" title="Generate static files"></a>Generate static files</h3><figure class="highlight bash"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">$ hexo generate</div></pre></td></tr></table></figure>
<p>More info: <a href="https://hexo.io/docs/generating.html" target="_blank" rel="external">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><figure class="highlight bash"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">$ hexo deploy</div></pre></td></tr></table></figure>
<p>More info: <a href="https://hexo.io/docs/deployment.html" target="_blank" rel="external">Deployment</a></p>
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<article id="post-campus-interview" class="article article-type-post" itemscope itemprop="blogPost">
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<a href="/2016/11/25/campus-interview/" class="article-date">
<time datetime="2016-11-25T12:49:35.000Z" itemprop="datePublished">2016-11-25</time>
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<a class="article-title" href="/2016/11/25/campus-interview/">2017互联网校园招聘的一些面试题</a>
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<div class="article-entry" itemprop="articleBody">
<h2 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h2><p>参加了2017年校招，面试了阿里、百度、腾讯、滴滴、美团、网易、去哪儿等公司，个人是客户端 Android 方向，总结了面试过程中频率出现较高的题目，希望对大家有所帮助。</p>
<h2 id="Java-一些知识点"><a href="#Java-一些知识点" class="headerlink" title="Java 一些知识点"></a>Java 一些知识点</h2><h3 id="Object-有哪些方法"><a href="#Object-有哪些方法" class="headerlink" title="Object 有哪些方法"></a>Object 有哪些方法</h3><ul>
<li><code>public</code> 方法：<code>getClass</code>、<code>equals</code>、<code>hashCode</code>、<code>toString</code>、<code>wait</code>、<code>notify</code></li>
<li><code>protected</code> 方法：<code>clone</code>、<code>finalize</code></li>
<li><code>private</code> 方法：<code>registerNatives</code>，该方法作用是将不同平台C/C++实现的方法映射到Java中的<code>native</code>方法</li>
</ul>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Object</span> </span>{</div><div class="line"> <span class="function"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">native</span> <span class="keyword">void</span> <span class="title">registerNatives</span><span class="params">()</span></span>;</div><div class="line"> <span class="comment">// 声明后有紧接静态代码块</span></div><div class="line"> <span class="keyword">static</span> {</div><div class="line"> registerNatives();</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h3 id="自动装箱"><a href="#自动装箱" class="headerlink" title="自动装箱"></a>自动装箱</h3><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>{</div><div class="line"> <span class="keyword">int</span> i = <span class="number">0</span>;</div><div class="line"> Integer j = <span class="keyword">new</span> Integer(<span class="number">0</span>);</div><div class="line"> System.out.println(j == i);</div><div class="line"> System.out.println(j.equals(i));</div><div class="line">}</div></pre></td></tr></table></figure>
<p>上述代码的输出是<br><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">true</span></div><div class="line"><span class="keyword">true</span></div></pre></td></tr></table></figure></p>
<h3 id="Java-虚拟机-GC-根节点的选择"><a href="#Java-虚拟机-GC-根节点的选择" class="headerlink" title="Java 虚拟机 GC 根节点的选择"></a>Java 虚拟机 GC 根节点的选择</h3><p>Java通过<strong>可达性分析</strong>来判断对象是否存活。基本思想是通过一系列称为”GC roots”的对象作为起始点，可以作为根节点的是：</p>
<ul>
<li>虚拟机栈（栈帧中的本地变量表）中引用的对象</li>
<li>本地方法栈中 JNI（即一般说的 Native 方法）引用的对象</li>
<li>方法区中类静态属性引用的对象</li>
<li>方法区中常量引用的对象</li>
</ul>
<p>笔者这么理解，作为GC Roots的节点主要在<strong>全局性</strong>的引用（例如常量或类静态属性）与<strong>执行上下文</strong>（例如栈帧中的本地变量表）中。<br>虚拟机栈、本地方法栈这都是局部变量，某个方法执行完，某些局部使用的对象可以被回收。</p>
<h3 id="类加载机制"><a href="#类加载机制" class="headerlink" title="类加载机制"></a>类加载机制</h3><ul>
<li><p>启动类加载器( Bootstrap ClassLoader)</p>
<p> 启动类加载器无法被 java 程序员直接引用, 这个类加载器负责把存放在<code><JAVA_HOME>\lib</code>目录中的, 或者被<code>-Xbootclasspath</code>参数指定路径中的, 并且是被虚拟机识别的类库加载到虚拟机内存中.</p>
</li>
<li><p>扩展类加载器(Extension ClassLoader)</p>
<p> 负责加载在<code><JAVA_HOME>\lib\ext</code>目录中的, 或者被<code>java.ext.dirs</code>系统变量所指定的路径中的所有类库。</p>
</li>
<li><p>应用程序类加载器( Application ClassLoader )</p>
<p> 这个类加载器是<code>ClassLoader</code> 中的 <code>getSystemClassLoader()</code>方法的返回值, 一般称其为系统类加载器, 它负责加载用户类路径( <code>ClassPath</code> )上所指定的类库</p>
</li>
</ul>
<p>从 java 虚拟机的角度而降, 只存在两种不同的类加载器：</p>
<ul>
<li><p>一个是启动类加载器( <code>Bootstrap ClassLoader</code> ), 这个类加载使用 C++ 语言实现, 是虚拟机自身的一部分;</p>
</li>
<li><p>另一种是其他所有的类加载器, 他们由 java 语言实现, 独立于虚拟机之外, 并且全部继承自<code>java.lang.ClassLoader</code></p>
</li>
</ul>
<p>加载类的寻找范围就是 JVM 默认路径加上<code>Classpath</code>, 类具体是使用哪个类加载器不确定。</p>
<h3 id="类加载主要步骤"><a href="#类加载主要步骤" class="headerlink" title="类加载主要步骤"></a>类加载主要步骤</h3><ul>
<li>加载 把 class 文件的二进制字节流加载到 jvm 里面</li>
<li>验证 确保 class 文件的字节流包含的信息符合当前 jvm 的要求 有文件格式验证, 元数据验证, 字节码验证, 符号引用验证等</li>
<li>准备 正式为类变量分配内存并设置类变量初始值的阶段, 初始化为各数据类型的零值</li>
<li>解析 把常量值内的符号引用替换为直接引用的过程</li>
<li>初始化 执行类构造器<code><clinit>()</code>方法</li>
<li>使用 根据相应的业务逻辑代码使用该类</li>
<li>卸载 类从方法区移除</li>
</ul>
<h3 id="双亲委派模型"><a href="#双亲委派模型" class="headerlink" title="双亲委派模型"></a>双亲委派模型</h3><p>除了顶层的启动类加载器之外, 其余的类加载器都应当有自己的父类加载器, 父子关系这儿一般都是以组合来实现。</p>
<p>工作过程: 如果一个类加载器收到了类加载的请求, 它首先不会自己去尝试加载这个类, 而是把这个请求委派给父类加载器去完成, 最终所有的加载请求都会传送到顶层的启动类加载器中, 只有当父类加载器反馈自己无法完成这个请求时候, 才由子加载器来加载。</p>
<p>例如类<code>Object</code>，它放在<code>rt.jar</code>中，无论哪一个类加载器要加载这个类，最终都是委派给启动类加载器进行加载，因此<code>Object</code>类在程序的各种类加载器环境中都是同一个类。</p>
<p>对于任何一个类, 都需要由加载它的类加载器和这个类本身一同确定其在 java 虚拟机中的唯一性。</p>
<p><code>ClassLoader.loadClass()</code>的代码如下，先检查是否已经被加载过，如果没有则<code>parent.loadClass()</code>调用父加载器的<code>loadClass()</code>方法，如果父加载器为空则默认使用启动类加载器作为父加载器。如果父类加载器加载失败，抛出<code>ClassNotFoundException</code>，再调用自己的<code>findClass()</code>方法进行加载。</p>
<p>另外，如果我们自己实现类加载器，一般是<code>Override</code>复写 <code>findClass</code>方法，而不是<code>loadClass</code>方法。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div></pre></td><td class="code"><pre><div class="line">protected Class<?> loadClass(String name, boolean resolve)</div><div class="line">throws ClassNotFoundException {</div><div class="line"> synchronized (getClassLoadingLock(name)) {</div><div class="line"> // First, check if the class has already been loaded</div><div class="line"> Class c = findLoadedClass(name);</div><div class="line"> if (c == null) {</div><div class="line"> long t0 = System.nanoTime();</div><div class="line"> try {</div><div class="line"> if (parent != null) {</div><div class="line"> c = parent.loadClass(name, false);</div><div class="line"> } else {</div><div class="line"> c = findBootstrapClassOrNull(name);</div><div class="line"> }</div><div class="line"> } catch (ClassNotFoundException e) {</div><div class="line"> // ClassNotFoundException thrown if class not found</div><div class="line"> // from the non-null parent class loader</div><div class="line"> }</div><div class="line"></div><div class="line"> if (c == null) {</div><div class="line"> // If still not found, then invoke findClass in order</div><div class="line"> // to find the class.</div><div class="line"> long t1 = System.nanoTime();</div><div class="line"> c = findClass(name); //可以Override该方法</div><div class="line"> }</div><div class="line"> }</div><div class="line"> if (resolve) {</div><div class="line"> resolveClass(c);</div><div class="line"> }</div><div class="line"> return c;</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="Java-后台的一点知识"><a href="#Java-后台的一点知识" class="headerlink" title="Java 后台的一点知识"></a>Java 后台的一点知识</h2><h3 id="JSP-与-Servlet-的关系"><a href="#JSP-与-Servlet-的关系" class="headerlink" title="JSP 与 Servlet 的关系"></a>JSP 与 Servlet 的关系</h3><ul>
<li>Tomcat 等 Web 容器最终会把 JSP转化为 Servlet</li>
<li>Jsp更擅长表现于页面显示, Servlet更擅长于逻辑控制</li>
<li>Servlet是利用 <code>System.out.println()</code>来输出 html 代码，由于包括大量的HTML标签、大量的静态文本及格式等，导致Servlet的开发效率低下</li>
<li>JSP通过在标准的HTML页面中嵌入Java代码，其静态的部分无须Java程序控制，Java 代码只控制那些动态生成的信息</li>
<li>最终 JSP 被容器解释为 Servlet，其中Html 代码也是用 <code>System.out.println()</code>等拼接输出的</li>
<li>JSP 第一次访问的时候，要转化为 java 文件，然后编译为 class 文件，所以第一次访问 JSP 速度会比较慢，后面会快很多</li>
</ul>
<h3 id="Servlet-生命周期"><a href="#Servlet-生命周期" class="headerlink" title="Servlet 生命周期"></a>Servlet 生命周期</h3><p>主要是<code>java.servlet.Servlet</code>接口中的<code>init()</code> 、<code>service()</code> 、和<code>destroy()</code> 3个方法。</p>
<ul>
<li>初始化阶段，web容器通过调用<code>init()</code>方法来初始化<code>Servlet</code>实例，在Servlet的整个生命周期类，<code>init()</code>方法只被调用一次</li>
<li>客户请求到来时，容器会开始一个新线程，并调用servlet的 <code>service()</code>方法，<code>service()</code> 方法根据请求的http方法来调用 <code>doget()</code> 或<code>dopost()</code></li>
<li>终止阶段调用<code>destroy()</code>方法，销毁一些资源</li>
</ul>
<h3 id="GET-请求-vs-POST-请求"><a href="#GET-请求-vs-POST-请求" class="headerlink" title="GET 请求 vs POST 请求"></a>GET 请求 vs POST 请求</h3><ul>
<li><code>GET</code>用于信息获取，是安全的和幂等的，<code>GET</code>一般是对后台数据库的信息进行查询</li>
<li><code>POST</code>表示可能修改变服务器上的资源的请求，一般是对后台数据库进行增、删、改的操作</li>
<li><code>GET</code>请求的参数会跟在URL后进行传递，请求的数据会附在URL之后，以<code>?</code>分割URL和传输数据，参数之间以<code>&</code>相连，一般浏览器对 URL 的长度会有限制</li>
<li><code>POST</code>请求，提交的数据则放置在是HTTP包的包体中，用类似<code>Key-Value</code>的格式发送一些数据，相对来说，<code>GET</code>请求会把请求的参数暴露在 URL 中，安全性比<code>POST</code>差一些</li>
</ul>
<h3 id="HTTP-请求的基本格式"><a href="#HTTP-请求的基本格式" class="headerlink" title="HTTP 请求的基本格式"></a>HTTP 请求的基本格式</h3><ul>
<li><<code>request line></code> 请求行</li>
<li><code><headers></code> 请求头（参数头）</li>
<li><code><blank line></code> 空白行</li>
<li><code>[<request-body>]</code> 请求实体（<code>GET没有， POST有</code>）</li>
</ul>
<h2 id="数据库"><a href="#数据库" class="headerlink" title="数据库"></a>数据库</h2><h3 id="索引的分类"><a href="#索引的分类" class="headerlink" title="索引的分类"></a>索引的分类</h3><p>主要分为聚集索引和非聚集索引：</p>
<ul>
<li>聚集索引存储记录物理上连续，而非聚集索引是逻辑上的连续，物理存储并不连续</li>
<li>聚集索引一个表只能有一个，而非聚集索引一个表可以存在多个</li>
</ul>
<h3 id="ResultSet-统计记录数目"><a href="#ResultSet-统计记录数目" class="headerlink" title="ResultSet 统计记录数目"></a>ResultSet 统计记录数目</h3><p>Java 中使用<code>JDBC</code>连接数据库，最后都会得到一个 ResultSet，比如如下的代码<br><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div></pre></td><td class="code"><pre><div class="line">Connection con = DriverManager.getConnection(url, username, password);</div><div class="line">Statement sta = con.createStatement();</div><div class="line">String sql = <span class="string">"select * from student"</span>;</div><div class="line">ResultSet resultSet = sta.executeQuery(sql);</div></pre></td></tr></table></figure></p>
<p>那么如何根据得到的<code>ResultSet</code>统计一共有多少条记录呢？注意：<code>ResultSet</code>没有提供类似<code>size()</code>、<code>length</code>的 API 来直接获取总记录数。</p>
<p>方法1：利用循环<br><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">int</span> sum = <span class="number">0</span>; </div><div class="line"><span class="keyword">while</span>(resultSet.next()){ </div><div class="line"> sum++; </div><div class="line">}</div></pre></td></tr></table></figure></p>
<p>方法2：利用ResultSet的getRow方法来获得ResultSet的总行数</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div></pre></td><td class="code"><pre><div class="line">resultSet.last(); //移到最后一行 </div><div class="line">int rowCount = resultSet.getRow(); //得到当前行号，也就是记录数 </div><div class="line">``` </div><div class="line"> </div><div class="line"></div><div class="line">## 设计模式 ##</div><div class="line"></div><div class="line">### 单例模式 ###</div><div class="line"></div><div class="line">单例模式中必须保证只有一个实例存在。有时候单例是为了避免重复创建多个实例造成资源浪费，有时候也是为了避免多个不同的实例导致系统不一致的行为。</div><div class="line"></div><div class="line">Android 中，App启动时系统会创建一个`Application`对象，用来存储系统的一些信息，这儿的`Application` 就是是单例模式的应用。可以通过`Context.getApplicationContext()`获取唯一的`Application`实例。</div><div class="line"></div><div class="line">```java</div><div class="line">class Singleton { </div><div class="line"> private volatile static Singleton instance; </div><div class="line"> </div><div class="line"> private Singleton() { } </div><div class="line"> </div><div class="line"> public static Singleton getInstance() { </div><div class="line"> //第一重判断 </div><div class="line"> if (instance == null) { </div><div class="line"> //锁定代码块 </div><div class="line"> synchronized (Singleton.class) { </div><div class="line"> //第二重判断 </div><div class="line"> if (instance == null) { </div><div class="line"> instance = new Singleton(); //创建单例实例 </div><div class="line"> } </div><div class="line"> } </div><div class="line"> } </div><div class="line"> return instance; </div><div class="line"> } </div><div class="line">}</div></pre></td></tr></table></figure>
<p>为什么<code>synchronized</code>里面需要加一次判断<code>if (instance == null)</code>，是考虑这样的特殊情形：比如线程A、B都到达<strong>第一个</strong><code>if (instance == null)</code>，线程A进入<code>synchronized</code>代码中创建实例，线程B排队等待。但当A执行完毕时，线程B进入<code>synchronized</code>锁定代码，它并不知道实例已经创建，将继续创建新的实例，导致产生多个单例对象。</p>
<p>也可以用内部类的方式创建，</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">public</span> class <span class="title">Singleton</span><span class="params">()</span></span>{</div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> <span class="class"><span class="keyword">class</span> <span class="title">Inner</span> </span>{</div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> Singleton instance = <span class="keyword">new</span> Singleton();</div><div class="line"> }</div><div class="line"> <span class="function"><span class="keyword">private</span> <span class="title">Singleton</span><span class="params">()</span> </span>{</div><div class="line"> }</div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> Singleton <span class="title">getInstance</span><span class="params">()</span></span>{</div><div class="line"> <span class="keyword">return</span> Inner.instance;</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h3 id="模板方法模式"><a href="#模板方法模式" class="headerlink" title="模板方法模式"></a>模板方法模式</h3><p>在父类中实现一个算法不变的部分，并将可变的行为留给子类来实现。</p>
<p>比如<code>AsyncTask</code> 里面的四个方法<code>onPreExecute</code>、<code>doInBackground</code>、<code>onProgressUpdate</code>、<code>onPostExecute</code></p>
<p>还有<code>Activity</code>也应用了模板方法模式<br><code>onCreate</code>、<code>onStart</code>、<code>onResume</code>、<code>onPause</code>、<code>onStop</code>、<code>onDestroy</code>、<code>onRestart</code></p>
<h3 id="适配器模式"><a href="#适配器模式" class="headerlink" title="适配器模式"></a>适配器模式</h3><p>分为两种：类的适配器模式、对象的适配器模式</p>
<p>Android 里的 <code>ListView</code> 和 <code>RecyclerView</code>的<code>setAdapter()</code>方法就是使用了适配器模式。</p>
<h3 id="观察者模式"><a href="#观察者模式" class="headerlink" title="观察者模式"></a>观察者模式</h3><p>在 GUI 中，不管是 Windows 桌面应用、或者 Android、IOS，都会给某个按钮 Button 设置监听事件，这儿就是使用了观察者模式。Android 中设置 Button 的监听事件代码如下：<br><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">final</span> Button button = (Button) findViewById(R.id.button_id);</div><div class="line">button.setOnClickListener(<span class="keyword">new</span> View.OnClickListener() {</div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onClick</span><span class="params">(View v)</span> </span>{</div><div class="line"> <span class="comment">// Perform action on click</span></div><div class="line"> }</div><div class="line">});</div></pre></td></tr></table></figure></p>
<h2 id="笔试编程题"><a href="#笔试编程题" class="headerlink" title="笔试编程题"></a>笔试编程题</h2><h3 id="线程-VS-进程"><a href="#线程-VS-进程" class="headerlink" title="线程 VS 进程"></a>线程 VS 进程</h3><p>关于线程和进程，不正确的描述是<em>__</em>。(选 D 栈是线程私有， 保存其运行状态和局部变量 )<br> A. 进程的隔离性要好于线程<br> B. 线程在资源消耗上通常要比进程轻量<br> C. 不同进程间不会共享逻辑地址空间<br> D. 同一个进程的线程之间共享内存，包括堆和栈<br> E. 进程间有途径共享大量内存中的数据<br> F. 线程间通讯可以通过直接访问全局变量，或者使用进程间通讯的机制(IPC)</p>
<h3 id="找出未打卡的员工"><a href="#找出未打卡的员工" class="headerlink" title="找出未打卡的员工"></a>找出未打卡的员工</h3><p>题目：输入两行数据，第一行为全部员工的 id，第二行为某一天打卡的员工 id，已知只有一个员工没有打卡，求出未打卡员工的 id。（员工 id 不重复，每行输入的 id 未排序）<br>输入：<br>1001 1003 1002 1005 1004<br>1002 1003 1001 1004<br>输出：<br>1005</p>
<p>分析：可以用两个 List，第一个 List 保存所有员工的 id，第二个 List 保存打卡员工的 id，从第一个List 中把第二个 List 的数据都删除，最终剩下的就是未打卡员工的 id。</p>
<p><strong>更好的方法</strong>：异或，两行数据中未打卡员工的 id 出现了一次，其余员工的 id 都出现了2次，两个相同的数异或为0。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div></pre></td><td class="code"><pre><div class="line">public static void main(String[] args) {</div><div class="line"> Scanner scan = new Scanner(System.in);</div><div class="line"> while (scan.hasNext()) {</div><div class="line"></div><div class="line"> String[] ids = scan.nextLine().split(" ");</div><div class="line"> String[] marks = scan.nextLine().split(" ");</div><div class="line"> int result = 0;</div><div class="line"> for (int i = 0; i < ids.length; i++) {</div><div class="line"> result ^= Integer.parseInt(ids[i]);</div><div class="line"> }</div><div class="line"> for (int i = 0; i < marks.length; i++) {</div><div class="line"> result ^= Integer.parseInt(marks[i]);</div><div class="line"> }</div><div class="line"> System.out.println(result);</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="手写代码题"><a href="#手写代码题" class="headerlink" title="手写代码题"></a>手写代码题</h2><h3 id="快速排序"><a href="#快速排序" class="headerlink" title="快速排序"></a>快速排序</h3><p>排序是经典面试题，公司也希望通过手写快排来考察面试者的编程习惯和基本功。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div></pre></td><td class="code"><pre><div class="line">// 排序范围 [start, end], 包含 end</div><div class="line">public void sort(int[] arr, int start, int end) {</div><div class="line"> if (start < end) {</div><div class="line"> int p = partition(arr, start, end);</div><div class="line"> quickSort(arr, start, p - 1);</div><div class="line"> quickSort(arr, p + 1, end);</div><div class="line"> }</div><div class="line">}</div><div class="line">// 一次划分代码，返回被划分后的基准位置</div><div class="line">public static int partition(int[] arr, int left, int right) {</div><div class="line"> int pivot = arr[left];</div><div class="line"> while (left < right) {</div><div class="line"> while (left < right && arr[right] >= pivot)</div><div class="line"> right--;</div><div class="line"> if (left < right)</div><div class="line"> arr[left++] = arr[right];</div><div class="line"> while (left < right && arr[left] <= pivot)</div><div class="line"> left++;</div><div class="line"> if (left < right)</div><div class="line"> arr[right--] = arr[left];</div><div class="line"> }</div><div class="line"> arr[left] = pivot;</div><div class="line"> return left;</div><div class="line">}</div></pre></td></tr></table></figure>
<p>Note：快排是不稳定的，常见的稳定排序是：冒泡、插入、归并</p>
<h3 id="括号字符串是否合法"><a href="#括号字符串是否合法" class="headerlink" title="括号字符串是否合法"></a>括号字符串是否合法</h3><p>某个字符串只包括<code>(</code>和<code>）</code>，判断其中的括号是否匹配正确，比如<code>(()())</code>正确，<code>((())()</code>错误，<code>不允许使用栈</code>。</p>
<p>这种类似题的常见思路是栈，对于左括号入栈，如果遇到右括号，判断此时栈顶是不是左括号，是则将其出栈，不是则该括号序列不合法。</p>
<p>面试官要求不能使用栈，可以使用计数器，利用<code>int count</code>字段。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div></pre></td><td class="code"><pre><div class="line">public static boolean checkBrackets(String str) {</div><div class="line"> char[] cs = str.toCharArray();</div><div class="line"> int count = 0;</div><div class="line"> for (int i = 0; i < cs.length; i++) {</div><div class="line"> if (cs[i] == '(')</div><div class="line"> count++;</div><div class="line"> else {</div><div class="line"> count--;</div><div class="line"> if (count < 0) {</div><div class="line"> return false;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"></div><div class="line"> return count == 0;</div><div class="line">}</div></pre></td></tr></table></figure>
<h3 id="扑克牌随机发牌"><a href="#扑克牌随机发牌" class="headerlink" title="扑克牌随机发牌"></a>扑克牌随机发牌</h3><p>对于52张牌，实现一个随机打算扑克牌顺序的程序。52张牌使用 <code>int</code> 数组模拟。</p>
<p>该算法的难点是如何保证随机性？有个经典算法<code>shuffle</code>，思路就是遍历数组，在剩下的元素里再随机取一个元素，然后再在剩下的元素里再随机取一个元素。每次取完元素后，我们就不会让这个元素参与下一次的选取。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div></pre></td><td class="code"><pre><div class="line">To shuffle an array a of n elements (indices 0..n-1):</div><div class="line"> for i from n − 1 downto 1 do</div><div class="line"> j ← random integer with 0 ≤ j ≤ i</div><div class="line"> exchange a[j] and a[i]</div></pre></td></tr></table></figure>
<p>注意这儿是<code>0 ≤ j ≤ i</code>，包括<code>j=i</code>的情况，因为可能洗牌后某个牌未发生交换，比如第51张牌还是原来的第51张牌。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">randomCards</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">int</span>[] data = <span class="keyword">new</span> <span class="keyword">int</span>[<span class="number">52</span>];</div><div class="line"> Random random= <span class="keyword">new</span> Random();</div><div class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> i = <span class="number">0</span>; i < data.length; i++)</div><div class="line"> data[i] = i;</div><div class="line"></div><div class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> i = data.length - <span class="number">1</span>; i > <span class="number">0</span>; i--) {</div><div class="line"> <span class="keyword">int</span> temp = random.nextInt(i+<span class="number">1</span>); <span class="comment">//产生 [0,i] 之间的随机数</span></div><div class="line"> swap(data,i,temp);</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="智力题"><a href="#智力题" class="headerlink" title="智力题"></a>智力题</h2><h3 id="金条付费"><a href="#金条付费" class="headerlink" title="金条付费"></a>金条付费</h3><p>你让工人为你工作7天，回报是一根金条，这个金条平分成相连的7段，你必须在每天结束的时候给他们一段金条，如果只允许你两次把金条弄断，你如何给你的工人付费？</p>
<p>答案：切成一段,两段,和四段.</p>
<p>第1天: 给出1.<br>第2天: 给出2,还回1.<br>第3天: 给出1.<br>第4天: 给出4,还回1+2.<br>第5天: 给出1.<br>第6天: 给出2,还回1.<br>第7天: 给出1.</p>
<h3 id="赛马"><a href="#赛马" class="headerlink" title="赛马"></a>赛马</h3><p>25匹马，速度都不同，但每匹马的速度都是定值。现在只有5条赛道，无法计时，即每赛一场最多只能知道5匹马的相对快慢。问最少赛几场可以找出25匹马中速度最快的前3名？</p>
<p>答案：</p>
<ul>
<li>25匹马分成5组，先进行<strong>5场</strong>比赛</li>
<li>再将刚才5场的冠军进行<strong>第6场</strong>比赛，得到第一名。按照第6场比赛的名词把前面5场比赛所在的组命名为 A、B、C、D、E 组，即 A 组的冠军是第6场第一名，B 组的冠军是第二名 …</li>
<li>分析第2名和第3名的可能性，如果确定有多于3匹马比某匹马快，那它可以被淘汰了。因为 D 组是第6场的第四名，整个D 组被淘汰了，同意整个 E 组被淘汰。剩下可能是整体的第2、3名的就是C组的第1名、B组的1、2名、A组的第2、3名。取这5匹马进行<strong>第7场</strong>比赛<br>-所以，一共需要7场比赛</li>
</ul>
<p>本文链接：<a href="http://www.codeceo.com/article/it-interview-question-2017.html" target="_blank" rel="external">http://www.codeceo.com/article/it-interview-question-2017.html</a></p>
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<a class="article-title" href="/2016/10/03/javac-error/">javac、javap命令行执行 java 程序的一点小坑</a>
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<h2 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h2><p>2016校园招聘季，正在复习 java，想使用 <code>javac</code> 、 <code>java</code> 、<code>javap</code>等命令分析<code>String s = "a" + "b" + "c" + "d"</code> 会创建几个对象，没想到执行<code>java</code> 命令总是报错。</p>
<p>本文链接 <a href="http://www.alijava.com/javac-error/" target="_blank" rel="external">http://www.alijava.com/javac-error/</a> 转载请注明出处</p>
<h2 id="代码"><a href="#代码" class="headerlink" title="代码"></a>代码</h2><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div></pre></td><td class="code"><pre><div class="line">TomChens-MBP:util tomchen$ pwd</div><div class="line">/Users/tomchen/Documents/javaEclipse/workspaceJava/OnlineOJ/src/util</div><div class="line">TomChens-MBP:util tomchen$ ls</div><div class="line">Main.java</div><div class="line">TomChens-MBP:util tomchen$ cat Main.java </div><div class="line"><span class="keyword">package</span> util; <span class="comment">//包名</span></div><div class="line"></div><div class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Main</span> </span>{</div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>{</div><div class="line"> String s = <span class="string">"a"</span> + <span class="string">"b"</span> + <span class="string">"c"</span> + <span class="string">"d"</span>;</div><div class="line"> System.out.println(s);</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<p><code>Main.java</code> 是在 Eclipse 工程下的<code>util</code>包里（<strong>注意就是这个 <code>util</code>包的影响</strong>！！）</p>
<h2 id="javac"><a href="#javac" class="headerlink" title="javac"></a>javac</h2><p>在目录<code>src/util</code> 执行 <code>javac</code>，没有问题</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line">TomChens-MBP:util tomchen$ javac Main.java </div><div class="line">TomChens-MBP:util tomchen$ ls</div><div class="line">Main.class Main.java</div></pre></td></tr></table></figure>
<ul>
<li><code>javac</code> 命令的使用方式是 <code>javac [文件名(带后缀名 .java)]</code></li>
<li><code>java</code> 命令是 <code>java [文件名(不带后缀名)]</code> </li>
</ul>
<h2 id="javap-字节码反编译"><a href="#javap-字节码反编译" class="headerlink" title="javap 字节码反编译"></a>javap 字节码反编译</h2><p>依然在目录<code>src/util</code>下执行<code>javap</code></p>
<figure class="highlight"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div><div class="line">65</div></pre></td><td class="code"><pre><div class="line">TomChens-MBP:util tomchen$ javap -c -v Main.class </div><div class="line">Classfile /Users/tomchen/Documents/javaEclipse/workspaceJava/OnlineOJ/src/util/Main.class</div><div class="line"> Last modified Oct 3, 2016; size 421 bytes</div><div class="line"> MD5 checksum 0700e51efd4656898d4c1c136394661f</div><div class="line"> Compiled from "Main.java"</div><div class="line">public class util.Main</div><div class="line"> SourceFile: "Main.java"</div><div class="line"> minor version: 0</div><div class="line"> major version: 51</div><div class="line"> flags: ACC_PUBLIC, ACC_SUPER</div><div class="line">Constant pool:</div><div class="line"> #1 = Methodref #6.#15 // java/lang/Object."<init>":()V</div><div class="line"> #2 = String #16 // abcd</div><div class="line"> #3 = Fieldref #17.#18 // java/lang/System.out:Ljava/io/PrintStream;</div><div class="line"> #4 = Methodref #19.#20 // java/io/PrintStream.println:(Ljava/lang/String;)V</div><div class="line"> #5 = Class #21 // util/Main</div><div class="line"> #6 = Class #22 // java/lang/Object</div><div class="line"> #7 = Utf8 <init></div><div class="line"> #8 = Utf8 ()V</div><div class="line"> #9 = Utf8 Code</div><div class="line"> #10 = Utf8 LineNumberTable</div><div class="line"> #11 = Utf8 main</div><div class="line"> #12 = Utf8 ([Ljava/lang/String;)V</div><div class="line"> #13 = Utf8 SourceFile</div><div class="line"> #14 = Utf8 Main.java</div><div class="line"> #15 = NameAndType #7:#8 // "<init>":()V</div><div class="line"> #16 = Utf8 abcd</div><div class="line"> #17 = Class #23 // java/lang/System</div><div class="line"> #18 = NameAndType #24:#25 // out:Ljava/io/PrintStream;</div><div class="line"> #19 = Class #26 // java/io/PrintStream</div><div class="line"> #20 = NameAndType #27:#28 // println:(Ljava/lang/String;)V</div><div class="line"> #21 = Utf8 util/Main</div><div class="line"> #22 = Utf8 java/lang/Object</div><div class="line"> #23 = Utf8 java/lang/System</div><div class="line"> #24 = Utf8 out</div><div class="line"> #25 = Utf8 Ljava/io/PrintStream;</div><div class="line"> #26 = Utf8 java/io/PrintStream</div><div class="line"> #27 = Utf8 println</div><div class="line"> #28 = Utf8 (Ljava/lang/String;)V</div><div class="line">{</div><div class="line"> public util.Main();</div><div class="line"> flags: ACC_PUBLIC</div><div class="line"> Code:</div><div class="line"> stack=1, locals=1, args_size=1</div><div class="line"> 0: aload_0 </div><div class="line"> 1: invokespecial #1 // Method java/lang/Object."<init>":()V</div><div class="line"> 4: return </div><div class="line"> LineNumberTable:</div><div class="line"> line 3: 0</div><div class="line"></div><div class="line"> public static void main(java.lang.String[]);</div><div class="line"> flags: ACC_PUBLIC, ACC_STATIC</div><div class="line"> Code:</div><div class="line"> stack=2, locals=2, args_size=1</div><div class="line"> 0: ldc #2 // String abcd</div><div class="line"> 2: astore_1 </div><div class="line"> 3: getstatic #3 // Field java/lang/System.out:Ljava/io/PrintStream;</div><div class="line"> 6: aload_1 </div><div class="line"> 7: invokevirtual #4 // Method java/io/PrintStream.println:(Ljava/lang/String;)V</div><div class="line"> 10: return </div><div class="line"> LineNumberTable:</div><div class="line"> line 5: 0</div><div class="line"> line 6: 3</div><div class="line"> line 7: 10</div><div class="line">}</div></pre></td></tr></table></figure>
<p>反编译主要是分析上面的<code>String s = "a" + "b" + "c" + "d";</code></p>
<p>由上面的<code>#2 = String #16 // abcd</code><br>可知：<code>"a" + "b" + "c" + "d"</code>只创建了一个对象，因为<code>"a""b""c""d"</code>等都是字符串常量，对于常量，在编译时候直接存储这几个常量拼接后的结果。</p>
<h2 id="java"><a href="#java" class="headerlink" title="java"></a>java</h2><p> 用惯了 Eclipse，想试下命令行输出，没想到执行<code>java</code>命令却老是报错</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div></pre></td><td class="code"><pre><div class="line">TomChens-MBP:util tomchen$ pwd</div><div class="line">/Users/tomchen/Documents/javaEclipse/workspaceJava/OnlineOJ/src/util</div><div class="line">TomChens-MBP:util tomchen$ java Main</div><div class="line">Exception in thread <span class="string">"main"</span> java.lang.NoClassDefFoundError: Main (wrong name: util/Main)</div><div class="line"> at java.lang.ClassLoader.defineClass1(Native Method)</div><div class="line"> at java.lang.ClassLoader.defineClass(ClassLoader.java:<span class="number">791</span>)</div><div class="line"> at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:<span class="number">142</span>)</div><div class="line"> at java.net.URLClassLoader.defineClass(URLClassLoader.java:<span class="number">449</span>)</div><div class="line"> at java.net.URLClassLoader.access$<span class="number">100</span>(URLClassLoader.java:<span class="number">71</span>)</div><div class="line"> at java.net.URLClassLoader$<span class="number">1</span>.run(URLClassLoader.java:<span class="number">361</span>)</div><div class="line"> at java.net.URLClassLoader$<span class="number">1</span>.run(URLClassLoader.java:<span class="number">355</span>)</div><div class="line"> at java.security.AccessController.doPrivileged(Native Method)</div><div class="line"> at java.net.URLClassLoader.findClass(URLClassLoader.java:<span class="number">354</span>)</div><div class="line"> at java.lang.ClassLoader.loadClass(ClassLoader.java:<span class="number">423</span>)</div><div class="line"> at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:<span class="number">308</span>)</div><div class="line"> at java.lang.ClassLoader.loadClass(ClassLoader.java:<span class="number">356</span>)</div><div class="line"> at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:<span class="number">482</span>)</div></pre></td></tr></table></figure>
<p>报了一堆问题，看网上的答案说可能是 CLASSPATH 的问题。</p>
<p>试验 <code>TomChens-MBP:util tomchen$ java -classpath . Main</code>还是不行。</p>
<p>怀疑可能是环境变量的问题，mac 的环境变量和 windows 有区别。</p>
<h2 id="Mac-设置-JAVA-HOME-和-PATH"><a href="#Mac-设置-JAVA-HOME-和-PATH" class="headerlink" title="Mac 设置 JAVA_HOME 和 PATH"></a>Mac 设置 JAVA_HOME 和 PATH</h2><p>设置 <code>JAVA_HOME</code>，网上找到一个方法，该方法的优点是没有把<code>JAVA_HOME</code>写死：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div></pre></td><td class="code"><pre><div class="line">// 编辑文件'~/.zshrc'或'~/.bash_profile'，加入下面两行：</div><div class="line">// 对于Java 1.7：</div><div class="line"></div><div class="line">export JAVA_HOME=`/usr/libexec/java_home -v 1.7`</div><div class="line">export PATH=${JAVA_HOME}/bin:$PATH</div></pre></td></tr></table></figure>
<p>对于 <code>CLASSPATH</code> ，网上大多意见是：不要设置全局的环境变量，每个应用会自己设置。有点疑惑？</p>
<ul>
<li>Mac OS X （Unix/Linux）中，路径分隔符是冒号(:)</li>
<li>Windows是分号（;）</li>
</ul>
<p>但是设置了环境变量还是没能解决上述的问题。</p>
<h2 id="package-的原因"><a href="#package-的原因" class="headerlink" title="package 的原因"></a>package 的原因</h2><p>后来看到一篇文章，发现要在 <code>src</code> 目录下执行 java 命令，而不是在<code>/src/util</code> 下执行。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div></pre></td><td class="code"><pre><div class="line">TomChens-MBP:util tomchen$ cd ..</div><div class="line">TomChens-MBP:src tomchen$ pwd</div><div class="line">/Users/tomchen/Documents/javaEclipse/workspaceJava/OnlineOJ/src</div><div class="line">TomChens-MBP:src tomchen$ java util.Main</div><div class="line">abcd</div><div class="line">TomChens-MBP:src tomchen$ java util/Main</div><div class="line">abcd</div></pre></td></tr></table></figure>
<p>可以看到，用<code>util.Main</code>或者<code>util/Main</code>指定包名都可以。</p>
<p>如果不是在<code>src</code>执行，而是在 <code>src/util</code>执行<code>java util/Main</code>，还是会报错</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div></pre></td><td class="code"><pre><div class="line">TomChens-MacBook-Pro:util tomchen$ pwd</div><div class="line">/Users/tomchen/Documents/javaEclipse/workspaceJava/OnlineOJ/src/util</div><div class="line">TomChens-MacBook-Pro:util tomchen$ java util/Main</div><div class="line">Error: Could not find or load main class util.Main</div></pre></td></tr></table></figure>
<h2 id="总结与思考"><a href="#总结与思考" class="headerlink" title="总结与思考"></a>总结与思考</h2><p> <code>javac</code> 命令与 <code>java</code> 命令的区别</p>
<ul>
<li><code>javac</code> 命令，在 <code>src</code>下执行<code>javac util/Main.java</code>可以，在<code>src/util</code>下执行<code>javac Main.java</code>也可以。</li>
<li>执行 <code>java</code> 命令需在 包的上层目录（比如包<code>util</code>的上层目录： <code>src</code>），并且类名前面要带上包名。因为Java存在类名相同但包名不同的情况，比如 <code>java.awt.List</code> 和<code>java.util.List</code>，包名+类名才能唯一识别某个类。</li>
<li>javac是一个<strong>平台命令</strong>，它对具体的平台文件进行操作，要指明<strong>被编译的文件路径</strong>。</li>
<li>java是一个<strong>虚拟机命令</strong>，它对类操作，即对类的描述要用点分的描述形式，并且不能加扩展名，还要注意类名的大小写。</li>
</ul>
<h2 id="参考文章"><a href="#参考文章" class="headerlink" title="参考文章"></a>参考文章</h2><ul>
<li><a href="http://www.raychase.net/1647" target="_blank" rel="external">常用的JDK自带命令行工具</a></li>
<li><a href="http://www.cnblogs.com/wangrui-techbolg/archive/2012/12/29/2839047.html" target="_blank" rel="external">Mac 终端命令运行java</a></li>
<li><a href="https://github.com/pubyun/macdev/blob/master/java.md" target="_blank" rel="external">Java开发环境的设置</a></li>
<li><a href="http://www.cnblogs.com/haolujun/archive/2013/03/02/2939698.html" target="_blank" rel="external">自己动手编译、运行Java程序</a></li>
</ul>
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<time datetime="2016-10-02T01:52:40.000Z" itemprop="datePublished">2016-10-02</time>
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<a class="article-title" href="/2016/10/02/sort-summary/">经典排序算法总结--冒泡、快排、插入、希尔、归并、选择</a>
</h1>
</header>
<div class="article-entry" itemprop="articleBody">
<h2 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h2><p>互联网面试，排序是经典问题，总结几种经典排序代码，方便后期查阅。</p>
<p>本文链接 <a href="http://www.alijava.com/sort-summary/" target="_blank" rel="external">http://www.alijava.com/sort-summary/</a> 转载请注明出处。</p>
<p>如何测试编写的排序代码? 可以利用在线编程OJ系统 ，比如牛客网的<br><a href="http://www.nowcoder.com/questionTerminal/508f66c6c93d4191ab25151066cb50ef" target="_blank" rel="external">http://www.nowcoder.com/questionTerminal/508f66c6c93d4191ab25151066cb50ef</a></p>
<h2 id="冒泡排序"><a href="#冒泡排序" class="headerlink" title="冒泡排序"></a>冒泡排序</h2><p>对纵向排列的关键字序列，按照自下而上的扫描方向对两两相邻的关键字进行比较，<br>若为逆序(k_j < k_j-1 )，则将两个记录交换位置；<br>重复上述扫描排序过程，直至没有记录需要交换为止。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">bubbleSort</span><span class="params">(<span class="keyword">int</span>[] arr, <span class="keyword">int</span> size)</span> </span>{</div><div class="line"> <span class="keyword">boolean</span> swap = <span class="keyword">false</span>;</div><div class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> i = <span class="number">0</span>; i < size - <span class="number">1</span>; i++) { <span class="comment">//最多进行 n-1 趟</span></div><div class="line"> swap = <span class="keyword">false</span>;</div><div class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> j = size - <span class="number">1</span>; j > i; j--) { <span class="comment">//从下往上扫描</span></div><div class="line"> <span class="keyword">if</span> (arr[j] < arr[j - <span class="number">1</span>]) {</div><div class="line"> swap(arr, j, j - <span class="number">1</span>);</div><div class="line"> swap = <span class="keyword">true</span>;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> <span class="keyword">if</span> (!swap) {</div><div class="line"> <span class="keyword">break</span>; <span class="comment">// 未发生交换，终止算法</span></div><div class="line"> }</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<p>冒泡排序的优化：<br>至多需要 n-1 趟扫描，如果在某趟扫描后，待排序记录已是有序，可以在此趟扫描后终止。<br>可引入布尔量<code>swap</code>，每次扫描前值为<code>false</code>，若排序过程中发生了交换，置为<code>true</code>。<br>在一趟扫描后，如果<code>swap</code>仍为<code>false</code>，表示本次未曾交换记录，可以终止算法。</p>
<h3 id="交换函数"><a href="#交换函数" class="headerlink" title="交换函数"></a>交换函数</h3><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">swap</span><span class="params">(<span class="keyword">int</span>[] arr, <span class="keyword">int</span> one, <span class="keyword">int</span> two)</span> </span>{</div><div class="line"> <span class="keyword">int</span> temp = arr[one];</div><div class="line"> arr[one] = arr[two];</div><div class="line"> arr[two] = temp;</div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="快速排序"><a href="#快速排序" class="headerlink" title="快速排序"></a>快速排序</h2><p>通过一趟排序将记录序列分成两个子序列，<br>再分别对这两个子序列进行排序以达到整个序列有序。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div></pre></td><td class="code"><pre><div class="line"><span class="comment">// 排序范围 [start, end], 包含 end </span></div><div class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">quickSort</span><span class="params">(<span class="keyword">int</span>[] arr, <span class="keyword">int</span> start, <span class="keyword">int</span> end)</span> </span>{</div><div class="line"> <span class="keyword">if</span> (start < end) {</div><div class="line"> <span class="keyword">int</span> p = partition(arr, start, end);</div><div class="line"> quickSort(arr, start, p - <span class="number">1</span>);</div><div class="line"> quickSort(arr, p + <span class="number">1</span>, end);</div><div class="line"> }</div><div class="line">}</div><div class="line"></div><div class="line"><span class="comment">// 一次划分代码，返回被划分后的基准位置</span></div><div class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">int</span> <span class="title">partition</span><span class="params">(<span class="keyword">int</span>[] arr, <span class="keyword">int</span> left, <span class="keyword">int</span> right)</span> </span>{</div><div class="line"> <span class="keyword">int</span> pivot = arr[left];</div><div class="line"> <span class="keyword">while</span> (left < right) {</div><div class="line"> <span class="keyword">while</span> (left < right && arr[right] >= pivot)</div><div class="line"> right--;</div><div class="line"> <span class="keyword">if</span> (left < right)</div><div class="line"> arr[left++] = arr[right];</div><div class="line"> <span class="keyword">while</span> (left < right && arr[left] <= pivot)</div><div class="line"> left++;</div><div class="line"> <span class="keyword">if</span> (left < right)</div><div class="line"> arr[right--] = arr[left];</div><div class="line"> }</div><div class="line"> arr[left] = pivot;</div><div class="line"> <span class="keyword">return</span> left;</div><div class="line">}</div></pre></td></tr></table></figure>
<p>快速排序的优化：<br>基准的选择影响快速排序的性能，最理想的情况是：选择的基准恰好能把待排序序列分成两个等长的子序列。</p>
<p>上文选择基准是固定使用序列的第1个元素，改进思路是：使用左端、右端和中间位置上的三个元素的<strong>中位数</strong>作为基准。</p>
<h2 id="非递归实现-快速排序"><a href="#非递归实现-快速排序" class="headerlink" title="非递归实现 快速排序"></a>非递归实现 快速排序</h2><p>思路就是用<strong>栈</strong>模拟递归</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">quickSort</span><span class="params">(<span class="keyword">int</span>[] arr, <span class="keyword">int</span> start, <span class="keyword">int</span> end)</span> </span>{</div><div class="line"> <span class="keyword">int</span>[] stack = <span class="keyword">new</span> <span class="keyword">int</span>[end - start + <span class="number">1</span>]; <span class="comment">// 数组模拟栈</span></div><div class="line"> <span class="keyword">int</span> len = <span class="number">0</span>;</div><div class="line"> stack[len++] = start; <span class="comment">// 入栈</span></div><div class="line"> stack[len++] = end;</div><div class="line"> <span class="keyword">while</span> (len > <span class="number">0</span>) { <span class="comment">// 栈中还有元素</span></div><div class="line"> <span class="keyword">int</span> right = stack[--len]; <span class="comment">// 注意是 --len</span></div><div class="line"> <span class="keyword">int</span> left = stack[--len];</div><div class="line"> <span class="keyword">int</span> p = partition(arr, left, right);</div><div class="line"> <span class="keyword">if</span> (p - <span class="number">1</span> > left) {</div><div class="line"> stack[len++] = left;</div><div class="line"> stack[len++] = p - <span class="number">1</span>;</div><div class="line"> }</div><div class="line"> <span class="keyword">if</span> (p + <span class="number">1</span> < right) {</div><div class="line"> stack[len++] = p + <span class="number">1</span>;</div><div class="line"> stack[len++] = right;</div><div class="line"> }</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="插入排序"><a href="#插入排序" class="headerlink" title="插入排序"></a>插入排序</h2><p>把关键字<code>k_i</code>依次与有序区的关键字<code>k_i-1</code>、<code>k_i-2</code>、··· 、<code>k_1</code>比较<br>找到应该插入的位置，将<code>k_i</code>插入，后面的序列要往后移动</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">insertSort</span><span class="params">(<span class="keyword">int</span>[] arr, <span class="keyword">int</span> size)</span> </span>{</div><div class="line"> <span class="keyword">int</span> temp = arr[<span class="number">0</span>];</div><div class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> i = <span class="number">1</span>; i < size; i++) {</div><div class="line"> <span class="comment">// 若 arr[i] 不小于有序区的最后一个元素，直接扩大有序区</span></div><div class="line"> <span class="keyword">if</span> (arr[i] < arr[i - <span class="number">1</span>]) { </div><div class="line"> temp = arr[i];</div><div class="line"> <span class="keyword">int</span> j = i - <span class="number">1</span>;</div><div class="line"> <span class="keyword">while</span> (j >= <span class="number">0</span> && temp < arr[j]) {</div><div class="line"> arr[j + <span class="number">1</span>] = arr[j--];</div><div class="line"> }</div><div class="line"> arr[j + <span class="number">1</span>] = temp;</div><div class="line"> }</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="希尔排序"><a href="#希尔排序" class="headerlink" title="希尔排序"></a>希尔排序</h2><p>插入排序当 n 较小时效率较高；当一组记录有序时，插入排序的算法复杂度可达到最优，即 O(n)。<br>希尔排序正是基于这两点对插入排序进行改进的。</p>
<p>希尔排序的基本思想：设置 t 个整数增量：<code>d_1</code>、<code>d_2</code>、···、<code>d_t</code>，其中<code>d_1 < n</code>, <code>d_t=1</code><br>以<code>d_1</code>为增量，将所有距离为<code>d_1</code>的记录放到同一个组，可以得到<code>d_1</code>个组，在各组内进行直接插入排序；<br>然后取第二个增量<code>d_2</code>，重复上述的分组和排序，直至增量<code>d_t=1</code></p>
<p>设置增量序列时，要使得增量值没有除 1 之外的公因子，最后一个增量值必须为 1。<br>希尔排序的时间复杂度取决于增量序列的选取。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div></pre></td><td class="code"><pre><div class="line">// shellSort(origins, origins.length, new int[] { 5, 3, 1 });</div><div class="line">public static void shellSort(int[] arr, int size, int[] d) {</div><div class="line"> for (int k = 0; k < d.length; k++) {</div><div class="line"> int gap = d[k];</div><div class="line"> for (int j = 0; j < gap; j++) { // 对于增量值 gap，一共 gap 组，0~gap-1</div><div class="line"> for (int i = j + gap; i < size; i++) {</div><div class="line"> if (arr[i] < arr[i - gap]) { // 如果大于，不需要插入排序</div><div class="line"> int pivot = arr[i];</div><div class="line"> int t = i - gap;</div><div class="line"> while (t >= 0 && pivot < arr[t]) {</div><div class="line"> arr[t + gap] = arr[t];</div><div class="line"> t = t - gap;</div><div class="line"> }</div><div class="line"> arr[t + gap] = pivot;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="归并排序"><a href="#归并排序" class="headerlink" title="归并排序"></a>归并排序</h2><p>归并的含义是：将两个或两个以上的有序表合并成一个新的有序表。<br>归并排序的思路是：<br>假设初始表含有 n 个记录，可看成是 n 个有序的子表，每个子表的长度为1，然后两两归并，<br>得到 n/2 个长度为 2 的有序子表，再两两归并，如此重复，直至得到长度为 n 的有序子表为止。</p>
<p>合并两个有序表：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div></pre></td><td class="code"><pre><div class="line">// 将arr[low]~arr[center]与arr[center+1]~arr[right]合并成有序表</div><div class="line">public static void merge(int[] arr, int left, int center, int right) {</div><div class="line"> int[] result = new int[right - left + 1];</div><div class="line"> int i = left, j = center + 1, k = 0;</div><div class="line"> while (i <= center && j <= right) {</div><div class="line"> if (arr[i] < arr[j])</div><div class="line"> result[k++] = arr[i++];</div><div class="line"> else</div><div class="line"> result[k++] = arr[j++];</div><div class="line"> }</div><div class="line"> while (i <= center)</div><div class="line"> result[k++] = arr[i++];</div><div class="line"> while (j <= right)</div><div class="line"> result[k++] = arr[j++];</div><div class="line"> System.arraycopy(result, 0, arr, left, right - left + 1);</div><div class="line">}</div></pre></td></tr></table></figure></p>
<p>一趟归并：<br>假设长度为<code>n</code>的待排序序列中，每个<strong>有序表</strong>的长度为 <code>step</code>，归并前共有<code>n/step</code>个子序列：<br><code>arr[0]~arr[step-1], arr[step]~arr[step*2-1], ···</code> ，一趟归并将相邻的一对有序表进行归并。<br>需要考虑三种情况：</p>
<ul>
<li>有序表的个数为偶数，且长度均为<code>step</code></li>
<li>有序表的个数为偶数，但最后一个有序表的长度小于<code>step</code></li>
<li>有序表的个数为奇数（轮空，不需要归并）</li>
</ul>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div></pre></td><td class="code"><pre><div class="line">// 子表的长度为 step，对数组进行一趟归并</div><div class="line">public static void mergePass(int[] arr, int step) {</div><div class="line"> int length = arr.length;</div><div class="line"> int i = 0;</div><div class="line"> // 循环，归并长度为 step 的两个有序表</div><div class="line"> for (; i + step * 2 - 1 < length; i += step * 2) {</div><div class="line"> merge(arr, i, i + step - 1, i + step * 2 - 1);</div><div class="line"> }</div><div class="line"> if (i + step < length)</div><div class="line"> merge(arr, i, i + step - 1, length - 1);</div><div class="line"> // 注意: 若 i + step >= length, 最后一个子表轮空，无需归并</div><div class="line">}</div></pre></td></tr></table></figure>
<p>归并排序时，有序表的初始长度为1，每趟归并后有序表长度增大一倍；<br>若干趟归并后，有序表的长度<code>>=n</code>，排序结束。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div></pre></td><td class="code"><pre><div class="line">public static void mergeSort(int[] arr, int size) {</div><div class="line"> for (int i = 1; i < size; i *= 2) {</div><div class="line"> mergePass(arr, i);</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="直接选择排序"><a href="#直接选择排序" class="headerlink" title="直接选择排序"></a>直接选择排序</h2><p>算法思路：第一趟排序将待排序记录 <code>arr[0]~arr[n-1]</code>作为无序区，从中找出最小的记录并与无序区<br>第1个记录<code>arr[0]</code>交换，此时得到有序区为<code>arr[0]</code>，无序区为<code>arr[1]~arr[n-1]</code>。<br>第二趟排序从<code>arr[1]~arr[n-1]</code>选出最小的记录，与<code>arr[1]</code>交换。<br>重复上述过程…</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div></pre></td><td class="code"><pre><div class="line">public static void selectSort(int[] arr, int size) {</div><div class="line"> for (int i = 0; i < size; i++) {</div><div class="line"> int min = i;</div><div class="line"> for (int j = i + 1; j < size; j++) {</div><div class="line"> if (arr[j] < arr[min])</div><div class="line"> min = j;</div><div class="line"> }</div><div class="line"> if (min != i)</div><div class="line"> swap(arr, min, i);</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="堆排序"><a href="#堆排序" class="headerlink" title="堆排序"></a>堆排序</h2><p>堆排序需要建立最小堆，参见这篇文章 <a href="http://www.alijava.com/heap-sort/" target="_blank" rel="external">http://www.alijava.com/heap-sort/</a></p>
<h2 id="排序汇总"><a href="#排序汇总" class="headerlink" title="排序汇总"></a>排序汇总</h2><table>
<thead>
<tr>
<th>排序算法</th>
<th style="text-align:center">平均时间复杂度</th>
<th style="text-align:center">最坏时间复杂度</th>
<th style="text-align:center">空间复杂度</th>
<th style="text-align:center">是否稳定</th>
</tr>
</thead>
<tbody>
<tr>
<td>冒泡</td>
<td style="text-align:center">O(n2)</td>
<td style="text-align:center">O(n2)</td>
<td style="text-align:center">O(1)</td>
<td style="text-align:center">稳定</td>
</tr>
<tr>
<td>快排</td>
<td style="text-align:center">O(nlogn)</td>
<td style="text-align:center">O(n2)</td>
<td style="text-align:center">O(logn)</td>
<td style="text-align:center">不稳定</td>
</tr>
<tr>
<td>插入</td>
<td style="text-align:center">O(n2)</td>
<td style="text-align:center">O(n2)</td>
<td style="text-align:center">O(1)</td>
<td style="text-align:center">稳定</td>
</tr>
<tr>
<td>希尔</td>
<td style="text-align:center">O(n1.3)</td>
<td style="text-align:center">O(n2)</td>
<td style="text-align:center">O(1)</td>
<td style="text-align:center">不稳定</td>
</tr>
<tr>
<td>归并</td>
<td style="text-align:center">O(nlogn)</td>
<td style="text-align:center">O(nlogn)</td>
<td style="text-align:center">O(n)</td>
<td style="text-align:center">稳定</td>
</tr>
<tr>
<td>选择</td>
<td style="text-align:center">O(n2)</td>
<td style="text-align:center">O(n2)</td>
<td style="text-align:center">O(1)</td>
<td style="text-align:center">不稳定</td>
</tr>
<tr>
<td>堆排序</td>
<td style="text-align:center">O(nlogn)</td>
<td style="text-align:center">O(nlogn)</td>
<td style="text-align:center">O(1)</td>
<td style="text-align:center">不稳定</td>
</tr>
</tbody>
</table>
<hr>
<p>利用递归实现快速排序，需要O(logn)的辅助空间;<br>归并排序大多数实现方法是O(logn)的辅助空间，少数是 O(1);<br>常见的稳定的排序为：冒泡、插入、归并。</p>
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<a class="article-title" href="/2016/09/22/heap-sort/">经典排序之 堆排序（附两种建堆思路及代码）</a>
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<h2 id="堆排序"><a href="#堆排序" class="headerlink" title="堆排序"></a>堆排序</h2><p>先做下记录，后序加上讲解<br>两种建立堆，一种就地，一种是插入</p>
<h2 id="buildMaxHeap"><a href="#buildMaxHeap" class="headerlink" title="buildMaxHeap"></a>buildMaxHeap</h2><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div><div class="line">65</div><div class="line">66</div></pre></td><td class="code"><pre><div class="line">import java.util.*;</div><div class="line"></div><div class="line">public class Main {</div><div class="line"></div><div class="line"> public static void main(String[] args) {</div><div class="line"></div><div class="line"> Scanner scan = new Scanner(System.in);</div><div class="line"> while (scan.hasNext()) {</div><div class="line"> int num = Integer.parseInt(scan.nextLine());</div><div class="line"> String[] inputs = scan.nextLine().split(" ");</div><div class="line"> int[] origins = new int[num];</div><div class="line"> int i = 0;</div><div class="line"> for (String s : inputs) {</div><div class="line"> origins[i++] = Integer.parseInt(s);</div><div class="line"> }</div><div class="line"></div><div class="line"> heapSort(origins, num);</div><div class="line"> for (int oi = num - 1; oi >= 0; oi--)</div><div class="line"> System.out.print(origins[oi] + " ");</div><div class="line"></div><div class="line"> System.out.println();</div><div class="line"> }</div><div class="line"> }</div><div class="line"></div><div class="line"> public static void heapSort(int[] arr, int length) {</div><div class="line"> buildHeapInPlace(arr, length);</div><div class="line"> for (int i = 0; i < length; i++) {</div><div class="line"> swap(arr, 0, length - 1 - i);</div><div class="line"> minHeap(arr, 0, length - 1 - i);</div><div class="line"> }</div><div class="line"></div><div class="line"> }</div><div class="line"></div><div class="line"> public static void buildHeapInPlace(int[] arr, int length) {</div><div class="line"> for (int i = (length - 1 - 1) >>> 1; i >= 0; i--)</div><div class="line"> minHeap(arr, i, length);</div><div class="line"></div><div class="line"> }</div><div class="line"></div><div class="line"> public static void minHeap(int[] arr, int mark, int length) {</div><div class="line"> int left = (mark << 1) + 1;</div><div class="line"> int right = (mark << 1) + 2;</div><div class="line"></div><div class="line"> while (left < length) {</div><div class="line"> int min = left;</div><div class="line"> if (right < length && arr[right] < arr[left])</div><div class="line"> min = right;</div><div class="line"></div><div class="line"> if (arr[min] < arr[mark]) {</div><div class="line"> swap(arr, min, mark);</div><div class="line"> mark = min;</div><div class="line"> left = (mark << 1) + 1;</div><div class="line"> right = (mark << 1) + 2;</div><div class="line"> } else {</div><div class="line"> break;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"></div><div class="line"> public static void swap(int[] arr, int one, int two) {</div><div class="line"> int temp = arr[one];</div><div class="line"> arr[one] = arr[two];</div><div class="line"> arr[two] = temp;</div><div class="line"> }</div><div class="line"></div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="maxHeapInsert"><a href="#maxHeapInsert" class="headerlink" title="maxHeapInsert"></a>maxHeapInsert</h2><p>逐个插入，建立堆</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div><div class="line">65</div><div class="line">66</div><div class="line">67</div><div class="line">68</div><div class="line">69</div><div class="line">70</div><div class="line">71</div><div class="line">72</div><div class="line">73</div><div class="line">74</div><div class="line">75</div><div class="line">76</div><div class="line">77</div><div class="line">78</div><div class="line">79</div><div class="line">80</div><div class="line">81</div><div class="line">82</div><div class="line">83</div><div class="line">84</div><div class="line">85</div><div class="line">86</div><div class="line">87</div><div class="line">88</div><div class="line">89</div><div class="line">90</div><div class="line">91</div><div class="line">92</div><div class="line">93</div><div class="line">94</div><div class="line">95</div><div class="line">96</div><div class="line">97</div><div class="line">98</div><div class="line">99</div><div class="line">100</div><div class="line">101</div><div class="line">102</div><div class="line">103</div><div class="line">104</div><div class="line">105</div><div class="line">106</div><div class="line">107</div><div class="line">108</div><div class="line">109</div><div class="line">110</div><div class="line">111</div><div class="line">112</div><div class="line">113</div><div class="line">114</div><div class="line">115</div><div class="line">116</div><div class="line">117</div><div class="line">118</div><div class="line">119</div><div class="line">120</div></pre></td><td class="code"><pre><div class="line">import java.util.*;</div><div class="line"></div><div class="line">public class Main {</div><div class="line"></div><div class="line"> public static void main(String[] args) {</div><div class="line"></div><div class="line"> Scanner scan = new Scanner(System.in);</div><div class="line"> while (scan.hasNext()) {</div><div class="line"> int num = Integer.parseInt(scan.nextLine());</div><div class="line"> String[] inputs = scan.nextLine().split(" ");</div><div class="line"> int[] origins = new int[num];</div><div class="line"> int i = 0;</div><div class="line"> for (String s : inputs) {</div><div class="line"> origins[i++] = Integer.parseInt(s);</div><div class="line"> }</div><div class="line"></div><div class="line"> heapSortTwo(origins, num);</div><div class="line"> for (int oi = num - 1; oi >= 0; oi--)</div><div class="line"> System.out.print(origins[oi] + " ");</div><div class="line"></div><div class="line"> System.out.println();</div><div class="line"> }</div><div class="line"> }</div><div class="line"></div><div class="line"></div><div class="line"> public static void heapSortTwo(int[] arr, int length) {</div><div class="line"> int[] copy = buildHeapInsert(arr, length);</div><div class="line"> for (int i = 0; i < length; i++) {</div><div class="line"> swap(copy, 0, length - 1 - i);</div><div class="line"> minHeapDown(copy, 0, length - 1 - i);</div><div class="line"> }</div><div class="line"> System.arraycopy(copy, 0, arr, 0, length);</div><div class="line"> }</div><div class="line"></div><div class="line"> /**</div><div class="line"> * 逐个插入建立最小堆</div><div class="line"> * @param arr</div><div class="line"> * @param length</div><div class="line"> */</div><div class="line"> public static int[] buildHeapInsert(int[] arr, int length) {</div><div class="line"> int[] heapArr = new int[length];</div><div class="line"> int heapLength = 0;</div><div class="line"> for (int i = 0; i < length; i++) {</div><div class="line"> heapArr[i] = arr[i];</div><div class="line"> minHeapUp(heapArr, i, ++heapLength);</div><div class="line"> }</div><div class="line"> return heapArr;</div><div class="line"> }</div><div class="line"></div><div class="line"></div><div class="line"> /**</div><div class="line"> * 维持堆的性质 上溯</div><div class="line"> * @param arr</div><div class="line"> * @param mark</div><div class="line"> * @param length</div><div class="line"> */</div><div class="line"> public static void minHeapUp(int[] arr, int mark, int length) {</div><div class="line"> int parent = (mark - 1) >> 1;</div><div class="line"> while (parent >= 0) {</div><div class="line"> if (arr[parent] > arr[mark]) {</div><div class="line"> swap(arr, parent, mark);</div><div class="line"> mark = parent;</div><div class="line"> parent = (mark - 1) >> 1;</div><div class="line"> } else {</div><div class="line"> break;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> </div><div class="line"> public static void heapSortOne(int[] arr, int length) {</div><div class="line"> buildHeapInPlace(arr, length);</div><div class="line"> for (int i = 0; i < length; i++) {</div><div class="line"> swap(arr, 0, length - 1 - i);</div><div class="line"> minHeapDown(arr, 0, length - 1 - i);</div><div class="line"> }</div><div class="line"> }</div><div class="line"> </div><div class="line"> /**</div><div class="line"> * 就地改变数组，建立堆</div><div class="line"> * @param arr</div><div class="line"> * @param length</div><div class="line"> */</div><div class="line"> public static void buildHeapInPlace(int[] arr, int length) {</div><div class="line"> for (int i = (length - 1 - 1) >>> 1; i >= 0; i--)</div><div class="line"> minHeapDown(arr, i, length);</div><div class="line"> }</div><div class="line"></div><div class="line"> /**</div><div class="line"> * 维持堆的性质 下溯</div><div class="line"> * @param arr</div><div class="line"> * @param mark</div><div class="line"> * @param length</div><div class="line"> */</div><div class="line"> public static void minHeapDown(int[] arr, int mark, int length) {</div><div class="line"> int left = (mark << 1) + 1;</div><div class="line"> int right = (mark << 1) + 2;</div><div class="line"></div><div class="line"> while (left < length) {</div><div class="line"> int min = left;</div><div class="line"> if (right < length && arr[right] < arr[left])</div><div class="line"> min = right;</div><div class="line"></div><div class="line"> if (arr[min] < arr[mark]) {</div><div class="line"> swap(arr, min, mark);</div><div class="line"> mark = min;</div><div class="line"> left = (mark << 1) + 1;</div><div class="line"> right = (mark << 1) + 2;</div><div class="line"> } else {</div><div class="line"> break;</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"></div><div class="line"> public static void swap(int[] arr, int one, int two) {</div><div class="line"> int temp = arr[one];</div><div class="line"> arr[one] = arr[two];</div><div class="line"> arr[two] = temp;</div><div class="line"> }</div><div class="line"></div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="备注"><a href="#备注" class="headerlink" title="备注"></a>备注</h2><p>可以通过这个牛客网 在线排序 OJ 检测自己排序算法</p>
<p><a href="http://www.nowcoder.com/questionTerminal/508f66c6c93d4191ab25151066cb50ef" target="_blank" rel="external">http://www.nowcoder.com/questionTerminal/508f66c6c93d4191ab25151066cb50ef</a></p>
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<a class="article-title" href="/2016/09/09/asynctask-analysis/">asynctask-analysis</a>
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<a class="article-title" href="/2016/09/03/array-copy/">深入解析 Java 数组 Arrays.copyOf 、Arrays.asList</a>
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<h1 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h1><p>java 数组定义和 C 语言中有些区别, <code>Arrays</code> 类提供了一些工具方法，本文总结了<code>copyOf()</code>、<code>asList()</code>使用过程中的一些注意点。</p>
<p>本文链接 <a href="http://www.alijava.com/array-copy/" target="_blank" rel="external">http://www.alijava.com/array-copy/</a> 转载请注明出处</p>
<h1 id="数组基础"><a href="#数组基础" class="headerlink" title="数组基础"></a>数组基础</h1><h2 id="定义数组"><a href="#定义数组" class="headerlink" title="定义数组"></a>定义数组</h2><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">int</span>[] a1 = { <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span> }; <span class="comment">//Java 风格</span></div><div class="line"><span class="keyword">int</span> a1[] = { <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span> }; <span class="comment">//C语言风格</span></div></pre></td></tr></table></figure>
<p><code>int[] a1</code>把<code>[]</code> 写在前面，更强调类型信息：数组<code>int[]</code></p>
<p><code>int[]</code> 也是继承了<code>Object</code>类, 而不是 <code>Object[]</code></p>
<p>数组可以创建时赋值，或者创建后再赋值</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">int</span>[] a2 = <span class="keyword">new</span> <span class="keyword">int</span>[] { <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span> };</div><div class="line"></div><div class="line"><span class="keyword">int</span> a3[] = <span class="keyword">new</span> <span class="keyword">int</span>[] { <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span> };</div><div class="line"></div><div class="line"><span class="keyword">int</span>[] a4 = <span class="keyword">new</span> <span class="keyword">int</span>[<span class="number">3</span>];</div><div class="line"></div><div class="line"><span class="keyword">for</span> (<span class="keyword">int</span> i = <span class="number">0</span>; i< a4.length; i++) </div><div class="line"> a4[i] = i;</div></pre></td></tr></table></figure>
<p>数组长度是 <code>length</code>，而字符串<code>String</code>获取长度是<code>length()</code></p>
<h2 id="foreach-循环"><a href="#foreach-循环" class="headerlink" title="foreach 循环"></a>foreach 循环</h2><p>JDK 5.0 引进了被称为<code>foreach</code>循环来遍历数组</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">for</span>(<span class="keyword">int</span> element: a4) </div><div class="line"> System.out.println(element);</div></pre></td></tr></table></figure>
<p>输出</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line"><span class="number">0</span></div><div class="line"><span class="number">1</span></div><div class="line"><span class="number">2</span></div></pre></td></tr></table></figure>
<h2 id="数组作为方法的参数"><a href="#数组作为方法的参数" class="headerlink" title="数组作为方法的参数"></a>数组作为方法的参数</h2><p>如果方法的参数是 <code>int[]</code> </p>
<ul>
<li>一是将变量传进去</li>
<li>二是匿名格式 <code>new int[] { 1, 2, 3 }</code>, 传<code>{ 1, 2, 3 }</code>是错误的</li>
</ul>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>{</div><div class="line"> <span class="comment">// testArr(a4); // 传入数组的引用，正确</span></div><div class="line"> </div><div class="line"> testArr(<span class="keyword">new</span> <span class="keyword">int</span>[] { <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span> });</div><div class="line"></div><div class="line"> <span class="comment">// compile error</span></div><div class="line"> <span class="comment">// testArr({ 1, 2, 3 });</span></div><div class="line"></div><div class="line"> <span class="comment">// compile error</span></div><div class="line"> <span class="comment">// testArr(1, 2, 3);</span></div><div class="line">}</div><div class="line"></div><div class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">testArr</span><span class="params">(<span class="keyword">int</span>[] nums)</span> </span>{</div><div class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> element : nums)</div><div class="line"> System.out.println(element);</div><div class="line">}</div></pre></td></tr></table></figure>
<p>输出</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line"><span class="number">1</span></div><div class="line"><span class="number">2</span></div><div class="line"><span class="number">3</span></div></pre></td></tr></table></figure>
<p>对于可变长参数的方法</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div></pre></td><td class="code"><pre><div class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">testVariPara</span><span class="params">(<span class="keyword">int</span>... nums)</span> </span>{</div><div class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> element : nums)</div><div class="line"> System.out.println(element);</div><div class="line">}</div></pre></td></tr></table></figure>
<p>下面这两种传递参数方法都可以正常运行</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">testVariPara(<span class="keyword">new</span> <span class="keyword">int</span>[] { <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span> });</div><div class="line">testVariPara(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>);</div></pre></td></tr></table></figure>
<h1 id="Arrays-工具类"><a href="#Arrays-工具类" class="headerlink" title="Arrays 工具类"></a>Arrays 工具类</h1><h2 id="toString-NaN"><a href="#toString-NaN" class="headerlink" title="toString"></a>toString</h2><p>Java 没有覆盖(<code>override</code>) 数组<code>int[]</code> 的toString()方法, 所以</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">System.out.println(a1.toString());</div></pre></td></tr></table></figure>
<p>得到结果 </p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">[I@<span class="number">182</span>da3d</div></pre></td></tr></table></figure>
<p>可以使用工具类 <code>Arrays</code> 输出数组</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">System.out.println(Arrays.toString(a1));</div></pre></td></tr></table></figure>
<p>输出</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>]</div></pre></td></tr></table></figure>
<h2 id="copyOf"><a href="#copyOf" class="headerlink" title="copyOf"></a>copyOf</h2><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">int</span>[] arr = {<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>,<span class="number">4</span>,<span class="number">5</span>};</div><div class="line"> </div><div class="line"><span class="keyword">int</span>[] copied = Arrays.copyOf(arr, <span class="number">10</span>); <span class="comment">//10 是数组的长度</span></div><div class="line">System.out.println(Arrays.toString(copied));</div><div class="line"> </div><div class="line">copied = Arrays.copyOf(arr, <span class="number">3</span>);</div><div class="line">System.out.println(Arrays.toString(copied));</div></pre></td></tr></table></figure>
<p>输出</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>]</div><div class="line">[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>]</div></pre></td></tr></table></figure>
<h2 id="区别-System-arraycopy"><a href="#区别-System-arraycopy" class="headerlink" title="区别 System.arraycopy()"></a>区别 System.arraycopy()</h2><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">int</span>[] arr = {<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>,<span class="number">4</span>,<span class="number">5</span>};</div><div class="line"> </div><div class="line"><span class="keyword">int</span>[] copied = <span class="keyword">new</span> <span class="keyword">int</span>[<span class="number">10</span>];</div><div class="line">System.arraycopy(arr, <span class="number">0</span>, copied, <span class="number">1</span>, <span class="number">5</span>);<span class="comment">// 5是需复制的元素个数</span></div><div class="line"> </div><div class="line">System.out.println(Arrays.toString(copied));</div></pre></td></tr></table></figure>
<p>输出<br><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">[<span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>]</div><div class="line">[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>, <span class="number">0</span>]</div></pre></td></tr></table></figure></p>
<p>查看 <code>Arrays.copyOf</code> 源码可知，它是新建了一个数组，然后利用<code>System.arraycopy</code> 将源数组复制到新数组中</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">int</span>[] copyOf(<span class="keyword">int</span>[] original, <span class="keyword">int</span> newLength) { </div><div class="line"> <span class="keyword">int</span>[] copy = <span class="keyword">new</span> <span class="keyword">int</span>[newLength]; </div><div class="line"> System.arraycopy(original, <span class="number">0</span>, copy, <span class="number">0</span>, Math.min(original.length, newLength)); </div><div class="line"> <span class="keyword">return</span> copy; </div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="asList-使用"><a href="#asList-使用" class="headerlink" title="asList 使用"></a>asList 使用</h2><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">int</span>[] a1 = { <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span> }; </div><div class="line">List<<span class="keyword">int</span>[]> list = Arrays.asList(a1); <span class="comment">// eclipse 提示修改为这样可以编译通过</span></div></pre></td></tr></table></figure>
<p>上面的很奇怪， <code>List<int></code> 和 <code>List<Integer></code> 会编译不通过，只能改为 <code>List<int[]></code> </p>
<p>转为 <code>List<int[]></code> 可以通过这样访问数组 <code>list.get(0)</code></p>
<p>为什么会这样呢？</p>
<p><code>List<int></code>编译错误，说明没有自动装箱和拆箱，<code>Arrays.asList</code>常见用法如下</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">List<Object> objList = Arrays.asList(obj1, obj2, obj3);</div></pre></td></tr></table></figure>
<p>上面代码将多个输入参数转化为 <code>List</code>，你也可以传入单个参数</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">List<Object> objList = Arrays.asList(obj1);</div></pre></td></tr></table></figure>
<p>而前面也提到了 <code>int[]</code>是一个对象，继承自<code>Object</code> , 所以返回了类型参数为 <code>int[]</code>的 <code>List</code></p>
<p>推荐 <code>Apache Commons ArrayUtils</code><br>下载地址 <a href="https://commons.apache.org/proper/commons-lang/download_lang.cgi" target="_blank" rel="external">https://commons.apache.org/proper/commons-lang/download_lang.cgi</a></p>
<p>它提供了很多工具方法，可以使用下面的代码处理 <code>int</code> 数组</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">List<Integer> exampleList = Arrays.asList(ArrayUtils.toObject(array));</div></pre></td></tr></table></figure>
<p>看下 API，<code>public static Integer[] toObject(int[] array)</code> 是将 <code>int[]</code> 转为 <code>Integer[]</code></p>
<p>也可以这么使用 <code>Arrays.asList</code> 来转化数组</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line">Integer[] a1 = { <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span> }; </div><div class="line">List<Integer> list = Arrays.asList(a1);</div><div class="line">System.out.println(list);</div></pre></td></tr></table></figure>
<p>或者这样</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">List<Integer> list = Arrays.asList(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>);</div><div class="line">System.out.println(list);</div></pre></td></tr></table></figure>
<h2 id="asList-定长"><a href="#asList-定长" class="headerlink" title="asList 定长"></a>asList 定长</h2><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">List<Integer> list = Arrays.asList(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>);</div><div class="line">list.add(<span class="number">44</span>); <span class="comment">// 抛出 UnsupportedOperationException</span></div></pre></td></tr></table></figure>
<p>上面的代码会抛出<code>java.lang.UnsupportedOperationException</code>异常</p>
<p>注意：<code>Arrays.asList</code>返回的是 <code>Arrays.ArrayList</code>，不是我们常用的<code>ArrayList</code></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div></pre></td><td class="code"><pre><div class="line"><span class="comment">// Arrays.ArrayList 源码</span></div><div class="line"><span class="keyword">private</span> <span class="keyword">static</span> <span class="class"><span class="keyword">class</span> <span class="title">ArrayList</span><<span class="title">E</span>> <span class="keyword">extends</span> <span class="title">AbstractList</span><<span class="title">E</span>> </span>{</div><div class="line"> <span class="function"><span class="keyword">public</span> E <span class="title">get</span><span class="params">(<span class="keyword">int</span> index)</span> </span>{</div><div class="line"> <span class="keyword">return</span> a[index];</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> E <span class="title">set</span><span class="params">(<span class="keyword">int</span> index, E element)</span> </span>{</div><div class="line"> E oldValue = a[index];</div><div class="line"> a[index] = element;</div><div class="line"> <span class="keyword">return</span> oldValue;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">indexOf</span><span class="params">(Object o)</span> </span>{</div><div class="line"> <span class="keyword">if</span> (o==<span class="keyword">null</span>) {</div><div class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> i=<span class="number">0</span>; i<a.length; i++)</div><div class="line"> <span class="keyword">if</span> (a[i]==<span class="keyword">null</span>)</div><div class="line"> <span class="keyword">return</span> i;</div><div class="line"> } <span class="keyword">else</span> {</div><div class="line"> <span class="keyword">for</span> (<span class="keyword">int</span> i=<span class="number">0</span>; i<a.length; i++)</div><div class="line"> <span class="keyword">if</span> (o.equals(a[i]))</div><div class="line"> <span class="keyword">return</span> i;</div><div class="line"> }</div><div class="line"> <span class="keyword">return</span> -<span class="number">1</span>;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">boolean</span> <span class="title">contains</span><span class="params">(Object o)</span> </span>{</div><div class="line"> <span class="keyword">return</span> indexOf(o) != -<span class="number">1</span>;</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<p><code>Arrays.asList</code> 不支持改变数组长度的操作（<code>add</code>、 <code>remove</code>等），看下源码，<code>Arrays.ArrayList</code>只实现了 <code>get</code>、 <code>set</code>、<code>indexOf</code>、<code>contains</code>等方法。</p>
<p><code>Arrays.ArrayList</code>的父类是<code>AbstractList</code>，它的 <code>add</code> 和 <code>set</code>都是<code>throw new UnsupportedOperationException()</code></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div></pre></td><td class="code"><pre><div class="line"><span class="comment">// AbstractList 源码</span></div><div class="line"><span class="keyword">public</span> <span class="keyword">abstract</span> <span class="class"><span class="keyword">class</span> <span class="title">AbstractList</span><<span class="title">E</span>> <span class="keyword">extends</span> <span class="title">AbstractCollection</span><<span class="title">E</span>> <span class="keyword">implements</span> <span class="title">List</span><<span class="title">E</span>> </span>{</div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">add</span><span class="params">(<span class="keyword">int</span> index, E element)</span> </span>{</div><div class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> UnsupportedOperationException();</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> E <span class="title">remove</span><span class="params">(<span class="keyword">int</span> index)</span> </span>{</div><div class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> UnsupportedOperationException();</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<p>如果需要得到支持<code>add</code>、<code>remove</code>的 <code>ArrayList</code>，可以这样</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">ArrayList<Integer> list = <span class="keyword">new</span> ArrayList<Integer>(Arrays.asList(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>));</div></pre></td></tr></table></figure>
<h2 id="集合转为数组"><a href="#集合转为数组" class="headerlink" title="集合转为数组"></a>集合转为数组</h2><p>ArrayList 可以转化为数组，有两个重载的方法</p>
<ul>
<li><code>Object[] toArray()</code></li>
<li><code><T> T[] toArray(T[] a)</code></li>
</ul>
<p>注意 <code>toArray()</code> 只能得到 <code>Object[]</code>，无法转型为具体数组类型，比如下面的代码会抛出<code>java.lang.ClassCastException</code>异常</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">List<Integer> list = <span class="keyword">new</span> ArrayList<>(Arrays.asList(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>));</div><div class="line">Integer[] arr = (Integer[]) list.toArray(); <span class="comment">// 抛出ClassCastException</span></div></pre></td></tr></table></figure>
<p>如果需要得到具体类型，需要使用<code>toArray(T[] a)</code>，传入参数<code>T[] a</code></p>
<ul>
<li><p>若<code>T[] a</code>长度<code><</code> 原来<code>list</code>的长度，则新建一个<code>list</code>的长度数组，填充元素并返回</p>
</li>
<li><p>若长度 <code>>=</code> <code>list</code>的长度，则把<code>list</code>元素填充<code>T[] a</code>，并返回<code>T[] a</code>的引用</p>
</li>
</ul>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div></pre></td><td class="code"><pre><div class="line">ArrayList<Integer> list = <span class="keyword">new</span> ArrayList<>(Arrays.asList(<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>));</div><div class="line"></div><div class="line">Integer[] a1 = <span class="keyword">new</span> Integer[<span class="number">2</span>];</div><div class="line">list.toArray(a1);</div><div class="line">System.out.println(Arrays.toString(a1));</div><div class="line"></div><div class="line">Integer[] a2 = <span class="keyword">new</span> Integer[<span class="number">3</span>];</div><div class="line">list.toArray(a2);</div><div class="line">System.out.println(Arrays.toString(a2));</div><div class="line"></div><div class="line">Integer[] a3 = <span class="keyword">new</span> Integer[<span class="number">4</span>];</div><div class="line">list.toArray(a3);</div><div class="line">System.out.println(Arrays.toString(a3));</div></pre></td></tr></table></figure>
<p>输出</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line">[null, null]</div><div class="line">[1, 2, 3]</div><div class="line">[1, 2, 3, null]</div></pre></td></tr></table></figure>
<p>也可以这么使用<code>String[] a = list.toArray(new String[0]);</code>，<code>new String[0]</code>只是为了类型信息</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div></pre></td><td class="code"><pre><div class="line"><span class="comment">// toArray(T[] a) 源码</span></div><div class="line"><span class="keyword">public</span> <T> T[] toArray(T[] a) {</div><div class="line"> <span class="keyword">if</span> (a.length < size)</div><div class="line"> <span class="comment">// Make a new array of a's runtime type, but my contents:</span></div><div class="line"> <span class="keyword">return</span> (T[]) Arrays.copyOf(elementData, size, a.getClass());</div><div class="line"> System.arraycopy(elementData, <span class="number">0</span>, a, <span class="number">0</span>, size);</div><div class="line"> <span class="keyword">if</span> (a.length > size)</div><div class="line"> a[size] = <span class="keyword">null</span>;</div><div class="line"> <span class="keyword">return</span> a;</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keyword">public</span> <span class="keyword">static</span> <T,U> T[] copyOf(U[] original, <span class="keyword">int</span> newLength, Class<? extends T[]> newType) {</div><div class="line"> T[] copy = ((Object)newType == (Object)Object[].class)</div><div class="line"> ? (T[]) <span class="keyword">new</span> Object[newLength]</div><div class="line"> : (T[]) Array.newInstance(newType.getComponentType(), newLength);</div><div class="line"> System.arraycopy(original, <span class="number">0</span>, copy, <span class="number">0</span>,</div><div class="line"> Math.min(original.length, newLength));</div><div class="line"> <span class="keyword">return</span> copy;</div><div class="line">}</div></pre></td></tr></table></figure>
<h1 id="参考文章"><a href="#参考文章" class="headerlink" title="参考文章"></a>参考文章</h1><ul>
<li><a href="http://stackoverflow.com/questions/12020886/how-arrays-aslistint-can-return-listint" target="_blank" rel="external">http://stackoverflow.com/questions/12020886/how-arrays-aslistint-can-return-listint</a></li>
</ul>
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<h1 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h1><p>Android Material Design越来越流行，以前很常用的 ListView 现在也用RecyclerView代替了，实现原理还是相似的。笔者实现一下 RecyclerView，代码比较简单，适合初学者，如有错误，欢迎指出。</p>
<p>源码地址（欢迎star） <a href="https://github.com/studychen/SeeNewsV2" target="_blank" rel="external">https://github.com/studychen/SeeNewsV2</a></p>
<p>本文链接 <a href="http://www.alijava.com/recyclerview-basics/" target="_blank" rel="external">http://www.alijava.com/recyclerview-basics/</a> 转载请注明出处</p>
<h1 id="复习-ListView"><a href="#复习-ListView" class="headerlink" title="复习 ListView"></a>复习 ListView</h1><p>ListView 实现过程中需要复写BaseAdapter，主要是这4个方法</p>
<ul>
<li><code>public int getCount()</code> ：适配器中数据集中 数据的个数，即ListView需要显示的数据个数</li>
<li><code>public Object getItem(int position)</code> ： 获取数据集中与指定索引对应的数据项 </li>
<li><code>public long getItemId(int position)</code> ： 获取指定行对应的ID </li>
<li><code>public View getView(int position, View convertView, ViewGroup parent)</code> ：获取每一个Item的显示内容</li>
</ul>
<blockquote>
<p>一般 <code>ListView</code> 每一项都是相同的布局，若想各个项实现不同的布局，可复写 <code>getItemViewType</code> 和 <code>getViewTypeCount</code>实现</p>
</blockquote>
<h1 id="RecyclerView-实现"><a href="#RecyclerView-实现" class="headerlink" title="RecyclerView 实现"></a>RecyclerView 实现</h1><h2 id="xml-布局"><a href="#xml-布局" class="headerlink" title="xml 布局"></a>xml 布局</h2><p><code>RecyclerView</code>中每一项的布局 <code>item_article_type_1.xml</code></p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div 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class="line">75</div><div class="line">76</div><div class="line">77</div><div class="line">78</div><div class="line">79</div><div class="line">80</div><div class="line">81</div><div class="line">82</div><div class="line">83</div><div class="line">84</div><div class="line">85</div><div class="line">86</div><div class="line">87</div><div class="line">88</div><div class="line">89</div><div class="line">90</div><div class="line">91</div></pre></td><td class="code"><pre><div class="line"><?xml version="1.0" encoding="utf-8"?></div><div class="line"><span class="tag"><<span class="name">android.support.v7.widget.CardView</span> <span class="attr">xmlns:android</span>=<span class="string">"http://schemas.android.com/apk/res/android"</span></span></div><div class="line"> <span class="attr">xmlns:card_view</span>=<span class="string">"http://schemas.android.com/apk/res-auto"</span></div><div class="line"> <span class="attr">xmlns:app</span>=<span class="string">"http://schemas.android.com/apk/res-auto"</span></div><div class="line"> <span class="attr">xmlns:fresco</span>=<span class="string">"http://schemas.android.com/apk/res-auto"</span></div><div class="line"> <span class="attr">android:id</span>=<span class="string">"@+id/cv_item"</span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"match_parent"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:foreground</span>=<span class="string">"?android:attr/selectableItemBackground"</span></div><div class="line"> <span class="attr">app:cardCornerRadius</span>=<span class="string">"5dp"</span></div><div class="line"> <span class="attr">app:cardElevation</span>=<span class="string">"5dp"</span></div><div class="line"> <span class="attr">app:contentPadding</span>=<span class="string">"2dp"</span>></div><div class="line"></div><div class="line"> <span class="tag"><<span class="name">LinearLayout</span></span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"match_parent"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"wrap_content"</span>></div><div class="line"></div><div class="line"> <span class="tag"><<span class="name">com.facebook.drawee.view.SimpleDraweeView</span></span></div><div class="line"> <span class="attr">android:id</span>=<span class="string">"@+id/rcv_article_photo"</span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"100dp"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"100dp"</span></div><div class="line"> <span class="attr">android:layout_centerVertical</span>=<span class="string">"true"</span></div><div class="line"> <span class="attr">fresco:actualImageScaleType</span>=<span class="string">"centerInside"</span></div><div class="line"> <span class="attr">fresco:roundAsCircle</span>=<span class="string">"true"</span></div><div class="line"> <span class="attr">fresco:roundingBorderColor</span>=<span class="string">"@color/lightslategray"</span></div><div class="line"> <span class="attr">fresco:roundingBorderWidth</span>=<span class="string">"1dp"</span> /></div><div class="line"></div><div class="line"> <span class="tag"><<span class="name">LinearLayout</span></span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"0dp"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"match_parent"</span></div><div class="line"> <span class="attr">android:layout_weight</span>=<span class="string">"1"</span></div><div class="line"> <span class="attr">android:orientation</span>=<span class="string">"vertical"</span>></div><div class="line"></div><div class="line"> <span class="tag"><<span class="name">TextView</span></span></div><div class="line"> <span class="attr">android:id</span>=<span class="string">"@+id/rcv_article_title"</span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:layout_marginLeft</span>=<span class="string">"10dp"</span></div><div class="line"> <span class="attr">android:layout_marginTop</span>=<span class="string">"2dp"</span></div><div class="line"> <span class="attr">android:gravity</span>=<span class="string">"center"</span></div><div class="line"> <span class="attr">android:text</span>=<span class="string">"关于举办《经典音乐作品欣赏与人文审美》讲座的通知"</span></div><div class="line"> <span class="attr">android:textColor</span>=<span class="string">"@color/primary_text"</span> /></div><div class="line"> <span class="comment"><!-- 新闻 发布时间 来源 阅读次数--></span></div><div class="line"> <span class="tag"><<span class="name">LinearLayout</span></span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"match_parent"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:layout_marginTop</span>=<span class="string">"5dp"</span></div><div class="line"> <span class="attr">android:gravity</span>=<span class="string">"center"</span></div><div class="line"> <span class="attr">android:orientation</span>=<span class="string">"horizontal"</span>></div><div class="line"></div><div class="line"> <span class="tag"><<span class="name">TextView</span></span></div><div class="line"> <span class="attr">android:id</span>=<span class="string">"@+id/rcv_article_date"</span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:layout_marginLeft</span>=<span class="string">"10dp"</span></div><div class="line"> <span class="attr">android:layout_marginRight</span>=<span class="string">"2dp"</span></div><div class="line"> <span class="attr">android:text</span>=<span class="string">"2015-01-09"</span> /></div><div class="line"></div><div class="line"> <span class="tag"><<span class="name">TextView</span></span></div><div class="line"> <span class="attr">android:id</span>=<span class="string">"@+id/rcv_article_source"</span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:layout_marginLeft</span>=<span class="string">"2dp"</span></div><div class="line"> <span class="attr">android:layout_marginRight</span>=<span class="string">"2dp"</span></div><div class="line"> <span class="attr">android:text</span>=<span class="string">"科学研究院"</span> /></div><div class="line"></div><div class="line"> <span class="tag"><<span class="name">TextView</span></span></div><div class="line"> <span class="attr">android:id</span>=<span class="string">"@+id/rcv_article_readtimes"</span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:layout_marginLeft</span>=<span class="string">"2dp"</span></div><div class="line"> <span class="attr">android:layout_marginRight</span>=<span class="string">"2dp"</span></div><div class="line"> <span class="attr">android:text</span>=<span class="string">"1129次"</span> /></div><div class="line"></div><div class="line"> <span class="tag"></<span class="name">LinearLayout</span>></span></div><div class="line"></div><div class="line"></div><div class="line"> <span class="tag"><<span class="name">TextView</span></span></div><div class="line"> <span class="attr">android:id</span>=<span class="string">"@+id/rcv_article_preview"</span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"wrap_content"</span></div><div class="line"> <span class="attr">android:layout_marginLeft</span>=<span class="string">"10dp"</span></div><div class="line"> <span class="attr">android:layout_marginTop</span>=<span class="string">"5dp"</span></div><div class="line"> <span class="attr">android:ellipsize</span>=<span class="string">"end"</span></div><div class="line"> <span class="attr">android:maxLines</span>=<span class="string">"2"</span></div><div class="line"> <span class="attr">android:text</span>=<span class="string">"讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识..."</span> /></div><div class="line"></div><div class="line"> <span class="tag"></<span class="name">LinearLayout</span>></span></div><div class="line"> <span class="tag"></<span class="name">LinearLayout</span>></span></div><div class="line"></div><div class="line"><span class="tag"></<span class="name">android.support.v7.widget.CardView</span>></span></div></pre></td></tr></table></figure>
<p>布局思路就是 <code>CardView</code>里面嵌入了一个<code>LinearLayout</code>。图片部分用固定宽度<code>100dp</code>，文字部分利用<code>android:layout_weight="1"</code>占据了其他部分。</p>
<p><code>TextView</code>利用<code>android:gravity="center"</code>使得标题的文字居中。</p>
<p><code>LinearLayout</code>里面利用<code>android:gravity="center"</code>使得<code>"2015-01-09 科学研究院 1129次"</code>居中，</p>
<p>新闻详情内容的<code>TextView</code>利用</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">android:maxLines="2"</div><div class="line">android:ellipsize="end"</div></pre></td></tr></table></figure>
<p>将文章内容限定为2行，超出部分用省略号显示。</p>
<p>预览效果</p>
<p><img src="http://img.blog.csdn.net/20160112111012393" alt="这里写图片描述"></p>
<p>新闻列表的 <code>xml</code> 文件，<code>fragment_article.xml</code></p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div></pre></td><td class="code"><pre><div class="line"><?xml version="1.0" encoding="utf-8"?></div><div class="line"><span class="tag"><<span class="name">LinearLayout</span> <span class="attr">xmlns:android</span>=<span class="string">"http://schemas.android.com/apk/res/android"</span></span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"match_parent"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"match_parent"</span></div><div class="line"> <span class="attr">android:orientation</span>=<span class="string">"vertical"</span>></div><div class="line"></div><div class="line"> <span class="tag"><<span class="name">android.support.v7.widget.RecyclerView</span></span></div><div class="line"> <span class="attr">android:id</span>=<span class="string">"@+id/rcv_article"</span></div><div class="line"> <span class="attr">android:layout_width</span>=<span class="string">"match_parent"</span></div><div class="line"> <span class="attr">android:layout_height</span>=<span class="string">"0dp"</span></div><div class="line"> <span class="attr">android:layout_weight</span>=<span class="string">"1"</span> /></div><div class="line"><span class="tag"></<span class="name">LinearLayout</span>></span></div></pre></td></tr></table></figure>
<h2 id="实现-Adapter"><a href="#实现-Adapter" class="headerlink" title="实现 Adapter"></a>实现 Adapter</h2><p>主要步骤是:</p>
<ul>
<li>根据上面的 <code>item_article_type_1.xml</code>实现一个 <code>class ImageItemArticleViewHolder extends RecyclerView.ViewHolder</code></li>
<li>实现<code>ItemArticleListAdapter extends RecyclerView.Adapter <></code><br>重写三个方法<ul>
<li><code>public int getItemCount()</code> </li>
<li><code>public TestAdapter.ImageItemArticleViewHolder onCreateViewHolder(ViewGroup parent, int viewType)</code> </li>
<li><code>public void onBindViewHolder(ImageItemArticleViewHolder holder, int position)</code> </li>
</ul>
</li>
</ul>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">ItemArticleAdapter</span> <span class="keyword">extends</span> <span class="title">RecyclerView</span>.<span class="title">Adapter</span><<span class="title">ItemArticleAdapter</span>.<span class="title">ImageItemArticleViewHolder</span>> </span>{</div><div class="line"></div><div class="line"> <span class="comment">//新闻列表</span></div><div class="line"> <span class="keyword">private</span> List<ItemArticle> articleList;</div><div class="line"></div><div class="line"> <span class="comment">//context</span></div><div class="line"> <span class="keyword">private</span> Context context;</div><div class="line"></div><div class="line"> <span class="keyword">private</span> LayoutInflater mLayoutInflater;</div><div class="line"></div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="title">ItemArticleAdapter</span><span class="params">(Context context,List<ItemArticle> articleList)</span> </span>{</div><div class="line"> <span class="keyword">this</span>.context = context;</div><div class="line"> <span class="keyword">this</span>.articleList = articleList;</div><div class="line"> mLayoutInflater = LayoutInflater.from(context);</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="keyword">public</span> ItemArticleAdapter.<span class="function">ImageItemArticleViewHolder <span class="title">onCreateViewHolder</span><span class="params">(ViewGroup parent, <span class="keyword">int</span> viewType)</span> </span>{</div><div class="line"> View view = mLayoutInflater.inflate(</div><div class="line"> R.layout.item_article_type_1, parent, <span class="keyword">false</span>);</div><div class="line"> <span class="keyword">return</span> <span class="keyword">new</span> ImageItemArticleViewHolder(view);</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onBindViewHolder</span><span class="params">(ImageItemArticleViewHolder holder, <span class="keyword">int</span> position)</span> </span>{</div><div class="line"> ItemArticle article = articleList.get(position);</div><div class="line"> holder.rcvArticlePhoto.setImageURI(Uri.parse(article.getImageUrl()));</div><div class="line"> holder.rcvArticleTitle.setText(article.getTitle());</div><div class="line"> holder.rcvArticleDate.setText(article.getPublishDate());</div><div class="line"> holder.rcvArticleSource.setText(article.getSource());</div><div class="line"> <span class="comment">//注意这个阅读次数是 int 类型，需要转化为 String 类型</span></div><div class="line"> holder.rcvArticleReadtimes.setText(article.getReadTimes()+<span class="string">"次"</span>);</div><div class="line"> holder.rcvArticlePreview.setText(article.getPreview());</div><div class="line"> }</div><div class="line"></div><div class="line"></div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">getItemCount</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">return</span> articleList.size();</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="class"><span class="keyword">class</span> <span class="title">ImageItemArticleViewHolder</span> <span class="keyword">extends</span> <span class="title">RecyclerView</span>.<span class="title">ViewHolder</span> </span>{</div><div class="line"></div><div class="line"> <span class="meta">@InjectView</span>(R.id.rcv_article_photo)</div><div class="line"> SimpleDraweeView rcvArticlePhoto;</div><div class="line"> <span class="meta">@InjectView</span>(R.id.rcv_article_title)</div><div class="line"> TextView rcvArticleTitle;</div><div class="line"> <span class="meta">@InjectView</span>(R.id.rcv_article_date)</div><div class="line"> TextView rcvArticleDate;</div><div class="line"> <span class="meta">@InjectView</span>(R.id.rcv_article_source)</div><div class="line"> TextView rcvArticleSource;</div><div class="line"> <span class="meta">@InjectView</span>(R.id.rcv_article_readtimes)</div><div class="line"> TextView rcvArticleReadtimes;</div><div class="line"> <span class="meta">@InjectView</span>(R.id.rcv_article_preview)</div><div class="line"> TextView rcvArticlePreview;</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="title">ImageItemArticleViewHolder</span><span class="params">(View itemView)</span> </span>{</div><div class="line"> <span class="keyword">super</span>(itemView);</div><div class="line"> ButterKnife.inject(<span class="keyword">this</span>, itemView);</div><div class="line"> }</div><div class="line"> }</div><div class="line"></div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="新闻实体类-javabean"><a href="#新闻实体类-javabean" class="headerlink" title="新闻实体类 javabean"></a>新闻实体类 javabean</h2><p>有新闻的 index，图片 url，标题，发布时间，来源，阅读次数，新闻内容预览<br><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div 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class="line">68</div><div class="line">69</div><div class="line">70</div><div class="line">71</div><div class="line">72</div><div class="line">73</div><div class="line">74</div><div class="line">75</div><div class="line">76</div><div class="line">77</div><div class="line">78</div><div class="line">79</div></pre></td><td class="code"><pre><div class="line"><span class="comment">/**</span></div><div class="line"> * 新闻类，这是在 RecycleView 使用的新闻 javabean</div><div class="line"> * 还有一个新闻详情javabean</div><div class="line"> */</div><div class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">ItemArticle</span> </span>{</div><div class="line"> <span class="keyword">private</span> <span class="keyword">int</span> index;</div><div class="line"> <span class="keyword">private</span> String imageUrl;</div><div class="line"> <span class="keyword">private</span> String title;</div><div class="line"> <span class="keyword">private</span> String publishDate;</div><div class="line"> <span class="keyword">private</span> String source;</div><div class="line"> <span class="keyword">private</span> <span class="keyword">int</span> readTimes;</div><div class="line"> <span class="keyword">private</span> String preview;</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="title">ItemArticle</span><span class="params">(<span class="keyword">int</span> index, String imageUrl, String title, String publishDate, String source, <span class="keyword">int</span> readTimes, String preview)</span> </span>{</div><div class="line"> <span class="keyword">this</span>.index = index;</div><div class="line"> <span class="keyword">this</span>.imageUrl = imageUrl;</div><div class="line"> <span class="keyword">this</span>.title = title;</div><div class="line"> <span class="keyword">this</span>.publishDate = publishDate;</div><div class="line"> <span class="keyword">this</span>.source = source;</div><div class="line"> <span class="keyword">this</span>.readTimes = readTimes;</div><div class="line"> <span class="keyword">this</span>.preview = preview;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">getIndex</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">return</span> index;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setIndex</span><span class="params">(<span class="keyword">int</span> index)</span> </span>{</div><div class="line"> <span class="keyword">this</span>.index = index;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> String <span class="title">getImageUrl</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">return</span> imageUrl;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setImageUrl</span><span class="params">(String imageUrl)</span> </span>{</div><div class="line"> <span class="keyword">this</span>.imageUrl = imageUrl;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> String <span class="title">getTitle</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">return</span> title;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setTitle</span><span class="params">(String title)</span> </span>{</div><div class="line"> <span class="keyword">this</span>.title = title;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> String <span class="title">getPublishDate</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">return</span> publishDate;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setPublishDate</span><span class="params">(String publishDate)</span> </span>{</div><div class="line"> <span class="keyword">this</span>.publishDate = publishDate;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> String <span class="title">getSource</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">return</span> source;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setSource</span><span class="params">(String source)</span> </span>{</div><div class="line"> <span class="keyword">this</span>.source = source;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">getReadTimes</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">return</span> readTimes;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setReadTimes</span><span class="params">(<span class="keyword">int</span> readTimes)</span> </span>{</div><div class="line"> <span class="keyword">this</span>.readTimes = readTimes;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> String <span class="title">getPreview</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">return</span> preview;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setPreview</span><span class="params">(String preview)</span> </span>{</div><div class="line"> <span class="keyword">this</span>.preview = preview;</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure></p>
<h2 id="fragment-里面使用-RecyclerView"><a href="#fragment-里面使用-RecyclerView" class="headerlink" title="fragment 里面使用 RecyclerView"></a>fragment 里面使用 RecyclerView</h2><p>思路就是开启一个异步线程，读取多条新闻，加入<code>List<ItemArticle></code>，由这个<code>List</code>构造<code>ItemArticleAdapter</code>，最后利用<code>setAdapter()</code>方法给<code>RecyclerView</code>加上适配器。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div 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class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> String STORE_PARAM = <span class="string">"param"</span>;</div><div class="line"> <span class="meta">@InjectView</span>(R.id.rcv_article)</div><div class="line"> RecyclerView rcvArticle;</div><div class="line"></div><div class="line"> <span class="keyword">private</span> String mParam;</div><div class="line"> <span class="comment">//新闻列表数据</span></div><div class="line"> <span class="keyword">private</span> List<ItemArticle> itemArticleList = <span class="keyword">new</span> ArrayList<ItemArticle>();</div><div class="line"></div><div class="line"> <span class="comment">//获取 fragment 依赖的 Activity，方便使用 Context</span></div><div class="line"> <span class="keyword">private</span> Activity mAct;</div><div class="line"></div><div class="line"></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> Fragment <span class="title">newInstance</span><span class="params">(String param)</span> </span>{</div><div class="line"> ArticleFragment fragment = <span class="keyword">new</span> ArticleFragment();</div><div class="line"> Bundle args = <span class="keyword">new</span> Bundle();</div><div class="line"> args.putString(STORE_PARAM, param);</div><div class="line"> fragment.setArguments(args);</div><div class="line"> <span class="keyword">return</span> fragment;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onCreate</span><span class="params">(Bundle savedInstanceState)</span> </span>{</div><div class="line"> <span class="keyword">super</span>.onCreate(savedInstanceState);</div><div class="line"> <span class="keyword">if</span> (getArguments() != <span class="keyword">null</span>) {</div><div class="line"> mParam = getArguments().getString(STORE_PARAM);</div><div class="line"> }</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="meta">@Nullable</span></div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="function"><span class="keyword">public</span> View <span class="title">onCreateView</span><span class="params">(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)</span> </span>{</div><div class="line"> View view = inflater.inflate(R.layout.fragment_article, <span class="keyword">null</span>);</div><div class="line"> Log.i(STORE_PARAM, <span class="string">"in StoreFragment"</span>);</div><div class="line"> mAct = getActivity();</div><div class="line"> ButterKnife.inject(<span class="keyword">this</span>, view);</div><div class="line"> <span class="keyword">return</span> view;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onActivityCreated</span><span class="params">(@Nullable Bundle savedInstanceState)</span> </span>{</div><div class="line"> <span class="keyword">super</span>.onActivityCreated(savedInstanceState);</div><div class="line"> rcvArticle.setLayoutManager(<span class="keyword">new</span> LinearLayoutManager(mAct));<span class="comment">//这里用线性显示 类似于listview</span></div><div class="line"><span class="comment">// rcvArticle.setLayoutManager(new GridLayoutManager(mAct, 2));//这里用线性宫格显示 类似于grid view</span></div><div class="line"><span class="comment">// rcvArticle.setLayoutManager(new StaggeredGridLayoutManager(2, OrientationHelper.VERTICAL));//这里用线性宫格显示 类似于瀑布流</span></div><div class="line"></div><div class="line"> <span class="keyword">new</span> LatestArticleTask().execute();</div><div class="line"></div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">onDestroyView</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">super</span>.onDestroyView();</div><div class="line"> ButterKnife.reset(<span class="keyword">this</span>);</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="class"><span class="keyword">class</span> <span class="title">LatestArticleTask</span> <span class="keyword">extends</span> <span class="title">AsyncTask</span><<span class="title">String</span>, <span class="title">Void</span>, <span class="title">List</span><<span class="title">ItemArticle</span>>> </span>{</div><div class="line"></div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">onPreExecute</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">super</span>.onPreExecute();</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="function"><span class="keyword">protected</span> List<ItemArticle> <span class="title">doInBackground</span><span class="params">(String... params)</span> </span>{</div><div class="line"> ItemArticle storeInfo1 =</div><div class="line"> <span class="keyword">new</span> ItemArticle(<span class="number">20123</span>, <span class="string">"http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG"</span>, <span class="string">"关于举办《经典音乐作品欣赏与人文审美》讲座的通知"</span>, <span class="string">"2015-01-09"</span>, <span class="string">"科学研究院"</span>, <span class="number">1129</span>,</div><div class="line"> <span class="string">"讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识..."</span>);</div><div class="line"> ItemArticle storeInfo2 =</div><div class="line"> <span class="keyword">new</span> ItemArticle(<span class="number">20123</span>, <span class="string">"http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG"</span>, <span class="string">"关于举办《经典音乐作品欣赏与人文审美》讲座的通知"</span>, <span class="string">"2015-01-09"</span>, <span class="string">"科学研究院"</span>, <span class="number">1129</span>,</div><div class="line"> <span class="string">"讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识..."</span>);</div><div class="line"> ItemArticle storeInfo3 =</div><div class="line"> <span class="keyword">new</span> ItemArticle(<span class="number">20123</span>, <span class="string">"http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG"</span>, <span class="string">"关于举办《经典音乐作品欣赏与人文审美》讲座的通知"</span>, <span class="string">"2015-01-09"</span>, <span class="string">"科学研究院"</span>, <span class="number">1129</span>,</div><div class="line"> <span class="string">"讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识..."</span>);</div><div class="line"> ItemArticle storeInfo4 =</div><div class="line"> <span class="keyword">new</span> ItemArticle(<span class="number">20123</span>, <span class="string">"http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG"</span>, <span class="string">"关于举办《经典音乐作品欣赏与人文审美》讲座的通知"</span>, <span class="string">"2015-01-09"</span>, <span class="string">"科学研究院"</span>, <span class="number">1129</span>,</div><div class="line"> <span class="string">"讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识..."</span>);</div><div class="line"> ItemArticle storeInfo5 =</div><div class="line"> <span class="keyword">new</span> ItemArticle(<span class="number">20123</span>, <span class="string">"http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG"</span>, <span class="string">"关于举办《经典音乐作品欣赏与人文审美》讲座的通知"</span>, <span class="string">"2015-01-09"</span>, <span class="string">"科学研究院"</span>, <span class="number">1129</span>,</div><div class="line"> <span class="string">"讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识..."</span>);</div><div class="line"> ItemArticle storeInfo6 =</div><div class="line"> <span class="keyword">new</span> ItemArticle(<span class="number">20123</span>, <span class="string">"http://i2.sinaimg.cn/ent/j/2012-05-20/U5912P28T3D3634984F328DT20120520152700.JPG"</span>, <span class="string">"关于举办《经典音乐作品欣赏与人文审美》讲座的通知"</span>, <span class="string">"2015-01-09"</span>, <span class="string">"科学研究院"</span>, <span class="number">1129</span>,</div><div class="line"> <span class="string">"讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识..."</span>);</div><div class="line"> itemArticleList.add(storeInfo1);</div><div class="line"> itemArticleList.add(storeInfo2);</div><div class="line"> itemArticleList.add(storeInfo3);</div><div class="line"> itemArticleList.add(storeInfo4);</div><div class="line"> itemArticleList.add(storeInfo5);</div><div class="line"> itemArticleList.add(storeInfo6);</div><div class="line"> <span class="keyword">return</span> itemArticleList;</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">onPostExecute</span><span class="params">(List<ItemArticle> data)</span> </span>{</div><div class="line"> <span class="keyword">super</span>.onPostExecute(data);</div><div class="line"> ItemArticleAdapter adapter = <span class="keyword">new</span> ItemArticleAdapter(mAct, data);</div><div class="line"> rcvArticle.setAdapter(adapter);</div><div class="line"> }</div><div class="line"> }</div><div class="line"></div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="效果图"><a href="#效果图" class="headerlink" title="效果图"></a>效果图</h2><p>利用修改布局，线性显示或者宫格显示 （以前宫格显示很麻烦，现在一条命令就好了）<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div></pre></td><td class="code"><pre><div class="line">rcvArticle.setLayoutManager(new LinearLayoutManager(mAct));//这里用线性显示 类似于listview</div><div class="line">// rcvArticle.setLayoutManager(new GridLayoutManager(mAct, 2));//这里用线性宫格显示 类似于grid view</div><div class="line">// rcvArticle.setLayoutManager(new StaggeredGridLayoutManager(2, OrientationHelper.VERTICAL));//这里用线性宫格显示 类似于瀑布流</div></pre></td></tr></table></figure></p>
<h2 id="效果图-1"><a href="#效果图-1" class="headerlink" title="效果图"></a>效果图</h2><p>线性布局</p>
<p><img src="http://img.blog.csdn.net/20160112101011378" width="300" height="550" alt="统计结果1" align="center"></p>
<p>线性宫格布局</p>
<p><img src="http://img.blog.csdn.net/20160112100848338" width="300" height="550" alt="统计结果1" align="center"></p>
<h1 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h1><h2 id="int-转化为-String"><a href="#int-转化为-String" class="headerlink" title="int 转化为 String"></a>int 转化为 String</h2><p><code>TextView</code> 有<code>setText(int resid)</code> 方法，但是这儿 <code>int</code> 表示 <code>resourceId</code>，如果我想把阅读次数（<code>int 1123</code>）赋给这个 <code>TextView</code>，不能使用这个方法。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div></pre></td><td class="code"><pre><div class="line"><span class="comment">//int 转 String 有三种方法</span></div><div class="line"><span class="keyword">int</span> i =<span class="number">8</span>;</div><div class="line">String s =Integer.toString(i);</div><div class="line">String g =String.valueOf(i);</div><div class="line">String h =i+<span class="string">""</span>;</div><div class="line">holder.rcvArticleReadtimes.setText(String.valueOf(article.getReadTimes()));</div></pre></td></tr></table></figure>
<h2 id="Todo-List"><a href="#Todo-List" class="headerlink" title="Todo List"></a>Todo List</h2><ul>
<li>Picasso 图片缓存库的学习</li>
<li>实现 RecyclerView 每个项各自的布局</li>
</ul>
<p>源码地址（欢迎star） <a href="https://github.com/studychen/SeeNewsV2" target="_blank" rel="external">https://github.com/studychen/SeeNewsV2</a> </p>
<h2 id="参考文章"><a href="#参考文章" class="headerlink" title="参考文章"></a>参考文章</h2><p><a href="http://javatechig.com/android/android-recyclerview-example" target="_blank" rel="external">Android RecyclerView Example | Java Techig</a></p>
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<time datetime="2016-09-03T03:13:07.000Z" itemprop="datePublished">2016-09-03</time>
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<a class="article-title" href="/2016/09/03/layout-gravity/">Android UI布局之区分 android:gravity 和 android:layout_gravity</a>
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<h1 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h1><p>在进行UI布局的时候，可能经常会用到 <code>android:gravity</code> 和 <code>android:layout_Gravity</code> 这两个属性。</p>
<p>本文链接 <a href="http://www.alijava.com/layout-gravity/" target="_blank" rel="external">http://www.alijava.com/layout-gravity/</a> 转载请注明出处</p>
<p><strong>一言以蔽之</strong></p>
<ul>
<li><p><code>android:gravity</code> 组件的子组件在组件中的位置</p>
</li>
<li><p><code>android:layout_gravity</code> 组件自身在父组件中的位置</p>
</li>
</ul>
<p>《第一行代码里》里的解释</p>
<ul>
<li><code>android:gravity</code>用于指定文字在控件中的对齐方式</li>
<li><code>android:layout_gravity</code>用于指定控件在布局中的对齐方式</li>
</ul>
<p>其实个人觉得两种说法并不矛盾，文字也可以理解为TextView的子组件，下面我们会看到<code>android:gravity</code>分别用于设置子组件或者文字。</p>
<p>网上还有一种总结是：</p>
<ul>
<li><p>名称不以layout_开头的属性作用于组件本身，组件生成时，会调用某个方法按照属性及属性值进行自我配置。</p>
</li>
<li><p>名称以layout_开头的属性作用于组件的父组件，称这些属性为<strong>布局参数</strong>，它们会告知父布局如何在内部安排自己的子元素。</p>
</li>
</ul>
<h1 id="android-gravity"><a href="#android-gravity" class="headerlink" title="android:gravity"></a>android:gravity</h1><p><code>android:gravity</code>用于指定<strong>文字在控件中的对齐方式</strong>（这儿将文字看作是子控件）</p>
<figure class="highlight"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div></pre></td><td class="code"><pre><div class="line"><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"</div><div class="line"> android:layout_width="match_parent"</div><div class="line"> android:layout_height="match_parent"</div><div class="line"> android:orientation="vertical" ></div><div class="line"> </div><div class="line"> <TextView</div><div class="line"> android:layout_width = "match_parent"</div><div class="line"> android:layout_height="wrap_content"</div><div class="line"> <!-- gravity 作用于文字 --></div><div class="line"> android:gravity="center"</div><div class="line"> android:textSize="24sp"</div><div class="line"> android:padding = "24dp"</div><div class="line"> android:text="this is text" /></div><div class="line"></div><div class="line"></LinearLayout></div></pre></td></tr></table></figure>
<p>效果见下图：</p>
<p><img src="http://img.blog.csdn.net/20150730213046307" width="300" height="450" alt="统计结果1" align="center"></p>
<hr>
<p>当然 <code>android:gravity="center"</code>也可以指定控件 <code>TextView</code> 在<code>LinearLayout</code>中居中，比如：</p>
<figure class="highlight"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div></pre></td><td class="code"><pre><div class="line"><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"</div><div class="line"> android:layout_width="match_parent"</div><div class="line"> android:layout_height="match_parent"</div><div class="line"> <!-- gravity 作用于子控件 TextView --></div><div class="line"> android:gravity="center"</div><div class="line"> android:orientation="vertical" ></div><div class="line"> </div><div class="line"> <TextView</div><div class="line"> android:layout_width = "match_parent"</div><div class="line"> android:layout_height="wrap_content"</div><div class="line"> android:gravity="center"</div><div class="line"> android:textSize="24sp"</div><div class="line"> android:padding = "24dp"</div><div class="line"> android:text="this is text" /></div><div class="line"></LinearLayout></div></pre></td></tr></table></figure>
<p>再看效果图：</p>
<p><img src="http://img.blog.csdn.net/20150730213328625" width="300" height="450" alt="统计结果1" align="center"></p>
<p><code>TextView</code>就居于<code>LinearLayout</code>的正中了。</p>
<ul>
<li><code>LinearLayout</code> 中<code>android:gravity="center"</code>表示<code>TextView</code>居于LinearLayout的正中间</li>
<li>而<code>TextView</code>的<code>android:gravity="center"</code>表示文字处于TextView的中间</li>
</ul>
<h1 id="android-layout-gravity"><a href="#android-layout-gravity" class="headerlink" title="android:layout_gravity"></a>android:layout_gravity</h1><p><code>android:layout_gravity</code>用于指定控件在布局中的对齐方式。注意，当<code>LinearLayout</code>是<code>vertical</code>时，只有水平方向上的对齐才会生效。</p>
<figure class="highlight"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div></pre></td><td class="code"><pre><div class="line"><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"</div><div class="line"> android:layout_width="match_parent"</div><div class="line"> android:layout_height="match_parent"</div><div class="line"> android:gravity="center"</div><div class="line"> android:orientation="vertical" ></div><div class="line"> </div><div class="line"> <TextView</div><div class="line"> android:layout_width = "match_parent"</div><div class="line"> android:layout_height="wrap_content"</div><div class="line"> android:gravity="center"</div><div class="line"> android:textSize="24sp"</div><div class="line"> android:padding = "24dp"</div><div class="line"> android:text="this is text" /></div><div class="line"> </div><div class="line"> <TextView</div><div class="line"> android:layout_width = "wrap_content"</div><div class="line"> android:layout_height="wrap_content"</div><div class="line"> android:gravity="center"</div><div class="line"> android:textSize="24sp"</div><div class="line"> android:padding = "24dp"</div><div class="line"> <!-- layout_gravity 作用于水平方向上 end --></div><div class="line"> android:layout_gravity="end"</div><div class="line"> android:text="another text" /></div><div class="line"></div><div class="line"></LinearLayout></div></pre></td></tr></table></figure>
<p>效果图：<br><img src="http://img.blog.csdn.net/20150730213924353" width="300" height="450" alt="统计结果1" align="center"></p>
<p>第2个<code>TextView</code>中，<code>android:gravity</code>表示这个<code>TextView</code>处于<code>LinearLayout</code>的中间，而<code>android:layout_gravity="end"</code>表示处于水平end的位置。</p>
<h1 id="最佳实践-完整示例"><a href="#最佳实践-完整示例" class="headerlink" title="最佳实践 完整示例"></a>最佳实践 完整示例</h1><figure class="highlight"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div><div class="line">35</div><div class="line">36</div><div class="line">37</div><div class="line">38</div><div class="line">39</div><div class="line">40</div><div class="line">41</div><div class="line">42</div><div class="line">43</div><div class="line">44</div><div class="line">45</div><div class="line">46</div><div class="line">47</div><div class="line">48</div><div class="line">49</div><div class="line">50</div><div class="line">51</div><div class="line">52</div><div class="line">53</div><div class="line">54</div><div class="line">55</div><div class="line">56</div><div class="line">57</div><div class="line">58</div><div class="line">59</div><div class="line">60</div><div class="line">61</div><div class="line">62</div><div class="line">63</div><div class="line">64</div><div class="line">65</div><div class="line">66</div><div class="line">67</div><div class="line">68</div><div class="line">69</div><div class="line">70</div><div class="line">71</div><div class="line">72</div><div class="line">73</div><div class="line">74</div><div class="line">75</div><div class="line">76</div><div class="line">77</div><div class="line">78</div><div class="line">79</div><div class="line">80</div><div class="line">81</div><div class="line">82</div><div class="line">83</div><div class="line">84</div><div class="line">85</div><div class="line">86</div><div class="line">87</div><div class="line">88</div><div class="line">89</div><div class="line">90</div><div class="line">91</div><div class="line">92</div><div class="line">93</div></pre></td><td class="code"><pre><div class="line"><?xml version="1.0" encoding="utf-8"?></div><div class="line"><android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"</div><div class="line"> xmlns:card_view="http://schemas.android.com/apk/res-auto"</div><div class="line"> xmlns:app="http://schemas.android.com/apk/res-auto"</div><div class="line"> xmlns:fresco="http://schemas.android.com/apk/res-auto"</div><div class="line"> android:id="@+id/cv_item"</div><div class="line"> android:layout_width="match_parent"</div><div class="line"> android:layout_height="wrap_content"</div><div class="line"> android:foreground="?android:attr/selectableItemBackground"</div><div class="line"> app:cardCornerRadius="5dp"</div><div class="line"> app:cardElevation="5dp"</div><div class="line"> app:contentPadding="2dp"></div><div class="line"></div><div class="line"> <LinearLayout</div><div class="line"> android:layout_width="match_parent"</div><div class="line"> android:layout_height="wrap_content"></div><div class="line"></div><div class="line"> <com.facebook.drawee.view.SimpleDraweeView</div><div class="line"> android:id="@+id/rcv_article_photo"</div><div class="line"> android:layout_width="100dp"</div><div class="line"> android:layout_height="100dp"</div><div class="line"> android:layout_centerVertical="true"</div><div class="line"> fresco:actualImageScaleType="centerInside"</div><div class="line"> fresco:roundAsCircle="true"</div><div class="line"> fresco:roundingBorderColor="@color/lightslategray"</div><div class="line"> fresco:roundingBorderWidth="1dp" /></div><div class="line"></div><div class="line"> <LinearLayout</div><div class="line"> android:layout_width="0dp"</div><div class="line"> android:layout_height="match_parent"</div><div class="line"> android:layout_weight="1"</div><div class="line"> android:orientation="vertical"></div><div class="line"></div><div class="line"> <TextView</div><div class="line"> android:id="@+id/rcv_article_title"</div><div class="line"> android:layout_width="wrap_content"</div><div class="line"> android:layout_height="wrap_content"</div><div class="line"> android:layout_marginLeft="10dp"</div><div class="line"> android:layout_marginTop="2dp"</div><div class="line"> <!-- gravity 文字居中 --></div><div class="line"> android:gravity="center"</div><div class="line"> android:text="关于举办《经典音乐作品欣赏与人文审美》讲座的通知"</div><div class="line"> android:textColor="@color/primary_text" /></div><div class="line"> <!-- 新闻 发布时间 来源 阅读次数--></div><div class="line"> <LinearLayout</div><div class="line"> android:layout_width="match_parent"</div><div class="line"> android:layout_height="wrap_content"</div><div class="line"> android:layout_marginTop="5dp"</div><div class="line"> <!-- 3个TextView居中 --></div><div class="line"> android:gravity="center"</div><div class="line"> android:orientation="horizontal"></div><div class="line"></div><div class="line"> <TextView</div><div class="line"> android:id="@+id/rcv_article_date"</div><div class="line"> android:layout_width="wrap_content"</div><div class="line"> android:layout_height="wrap_content"</div><div class="line"> android:layout_marginLeft="10dp"</div><div class="line"> android:layout_marginRight="2dp"</div><div class="line"> android:text="2015-01-09" /></div><div class="line"></div><div class="line"> <TextView</div><div class="line"> android:id="@+id/rcv_article_source"</div><div class="line"> android:layout_width="wrap_content"</div><div class="line"> android:layout_height="wrap_content"</div><div class="line"> android:layout_marginLeft="2dp"</div><div class="line"> android:layout_marginRight="2dp"</div><div class="line"> android:text="科学研究院" /></div><div class="line"></div><div class="line"> <TextView</div><div class="line"> android:id="@+id/rcv_article_readtimes"</div><div class="line"> android:layout_width="wrap_content"</div><div class="line"> android:layout_height="wrap_content"</div><div class="line"> android:layout_marginLeft="2dp"</div><div class="line"> android:layout_marginRight="2dp"</div><div class="line"> android:text="1129次" /></div><div class="line"></div><div class="line"> </LinearLayout></div><div class="line"></div><div class="line"></div><div class="line"> <TextView</div><div class="line"> android:id="@+id/rcv_article_preview"</div><div class="line"> android:layout_width="wrap_content"</div><div class="line"> android:layout_height="wrap_content"</div><div class="line"> android:layout_marginLeft="10dp"</div><div class="line"> android:layout_marginTop="5dp"</div><div class="line"> android:ellipsize="end"</div><div class="line"> android:maxLines="2"</div><div class="line"> android:text="讲座主要内容：以中、西方音乐历史中经典音乐作品为基础，通过作曲家及作品创作背景、相关音乐文化史知识及音乐欣赏常识..." /></div><div class="line"></div><div class="line"> </LinearLayout></div><div class="line"> </LinearLayout></div><div class="line"></div><div class="line"></android.support.v7.widget.CardView></div></pre></td></tr></table></figure>
<p>效果图<br><img src="http://img.blog.csdn.net/20160112111012393" alt="这里写图片描述" title=""></p>
<h1 id="思路"><a href="#思路" class="headerlink" title="思路"></a>思路</h1><p>这是自己项目中的一个记录，具体可参照这篇文章<br>Android Material Design学习之RecyclerView代替 ListView <a href="http://www.alijava.com/recyclerview-basics/" target="_blank" rel="external">http://www.alijava.com/recyclerview-basics/</a></p>
<hr>
<p>布局思路就是 <code>CardView</code>里面嵌入了一个<code>LinearLayout</code>。</p>
<p>图片部分用固定宽度<code>100dp</code>，文字部分利用<code>android:layout_weight="1"</code>占据了其他部分。</p>
<p><code>TextView</code>利用<code>android:gravity=”center”</code>使得标题的文字居中。</p>
<p><code>LinearLayout</code>里面利用<code>android:gravity="center"</code>使得<code>"2015-01-09 科学研究院 1129次"</code>居中，</p>
<p>新闻详情内容的<code>TextView</code>利用</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div></pre></td><td class="code"><pre><div class="line">android:maxLines="2"</div><div class="line">android:ellipsize="end"</div></pre></td></tr></table></figure>
<p>将文章内容限定为2行，超出部分用省略号显示。</p>
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<ul class="tag-list"><li class="tag-list-item"><a class="tag-list-link" href="/tags/Android/">Android</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Java/">Java</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Linux/">Linux</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/MaterialDesign/">MaterialDesign</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/Python/">Python</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/七牛/">七牛</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/命令行/">命令行</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/工具/">工具</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/排序/">排序</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/数组/">数组</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/爬虫/">爬虫</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/网络/">网络</a></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/面试/">面试</a></li></ul>
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