<blockquote>Java中if语句用于条件判断，核心是布尔表达式，支持if、if-else、if-else if-else及嵌套结构；正确使用比较与逻辑运算符可避免常见错误，短路运算符提升安全性；嵌套过深影响可读性，可通过合并条件、提取方法或使用卫语句优化；三元运算符适用于简单赋值，卫语句模式通过提前返回减少嵌套，提升代码清晰度与维护性。</blockquote> <p><img src=”https://img.php.cn/upload/article/001/503/042/175552170793286.jpeg” alt=”java如何用if语句进行简单条件判断 java条件判断语句的入门教程”></p> <p>Java中，<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>语句是进行条件判断的基础，它允许你的程序根据某个条件是否成立来执行不同的代码块。这是控制程序流程最直接、最常用的方式，可以说，没有它，很多程序的逻辑就无从谈起。</p> <h2>解决方案</h2> <p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>语句的核心思想是“如果这样，就那样”。最简单的形式是：当一个条件为真时，执行一段代码。</p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:java;toolbar:false;’>public class ConditionDemo { public static void main(String[] args) { int score = 85; // 最基本的if语句：如果条件为真，执行括号内的代码 if (score >= 60) { System.out.println("恭喜你，考试及格了！"); } // if-else语句：如果条件为真执行if块，否则执行else块 if (score >= 90) { System.out.println("你真是个学霸！"); } else { System.out.println("还需要继续努力哦。"); } // if-else if-else语句：多条件判断，按顺序检查，遇到第一个真就执行对应块 if (score >= 90) { System.out.println("成绩优秀！"); } else if (score >= 80) { // 只有当score < 90 且 score >= 80 时才执行 System.out.println("成绩良好。"); } else if (score >= 60) { // 只有当score < 80 且 score >= 60 时才执行 System.out.println("成绩合格。"); } else { // 以上条件都不满足时执行 System.out.println("成绩不合格，需要补考。"); } // 也可以不带else，多个if语句可以独立存在 boolean isSunny = true; if (isSunny) { System.out.println("今天天气真好，出去走走吧。"); } int temperature = 25; if (temperature > 20) { System.out.println("有点热。"); } if (temperature < 30) { // 这个条件也可能同时满足 System.out.println("不算太热。"); } } }</pre><div class=”contentsignin”></div></div><p>这里面，<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>后面括号里的内容就是所谓的“条件”，它必须是一个能够评估出<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>true</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>或<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>false</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>的布尔表达式。只要这个表达式的结果是<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>true</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>，<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>后面紧跟着的代码块（通常用花括号<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>{}</pre><div class=”contentsignin”></div></div>括起来）就会被执行。如果条件是<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>false</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>，那么<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>块就会被跳过。而<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>else</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>和<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>else if</pre><div class=”contentsignin”></div></div>则提供了更复杂的路径选择。</p> <h3>Java if语句中的布尔表达式：常见误区与正确写法</h3> <p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>语句的灵魂在于其后的布尔表达式。一个正确的布尔表达式是确保你的条件判断逻辑准确无误的关键。我发现很多初学者，甚至一些有经验的开发者，偶尔也会在这里犯一些小错误。</p> <p><span>立即学习</span>“<a href=”https://pan.quark.cn/s/c1c2c2ed740f” style=”text-decoration: underline !important; color: blue; font-weight: bolder;” rel=”nofollow” target=”_blank”>Java免费学习笔记（深入）</a>”；</p> <p>布尔表达式通常由以下几类构成：</p> <ol> <li> <p><strong>比较运算符：</strong></p> <ul> <li><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>==</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> (等于)</li> <li><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>!=</pre><div class=”contentsignin”></div></div> (不等于)</li> <li><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”><</pre><div class=”contentsignin”></div></div> (小于)</li> <li><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>></pre><div class=”contentsignin”></div></div> (大于)</li> <li><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”><=</pre><div class=”contentsignin”></div></div> (小于等于)</li> <li><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>>=</pre><div class=”contentsignin”></div></div> (大于等于) 例如：<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>age > 18</pre><div class=”contentsignin”></div></div>，<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>name.equals("Alice")</pre><div class=”contentsignin”></div></div>（注意，比较字符串内容要用<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>equals()</pre><div class=”contentsignin”></div></div>而不是<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>==</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>，<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>==</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>比较的是对象的引用地址）。</li> </ul> </li> <li> <p><strong>逻辑运算符：</strong></p> <ul> <li><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>&&</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> (逻辑与，AND)：两边都为真才为真。<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>score >= 60 && score < 70</pre><div class=”contentsignin”></div></div></li> <li><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>||</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div> (逻辑或，OR)：只要一边为真就为真。<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>isStudent || isTeacher</pre><div class=”contentsignin”></div></div></li> <li><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>!</pre><div class=”contentsignin”></div></div> (逻辑非，NOT)：取反。<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>!isEmpty</pre><div class=”contentsignin”></div></div></li> </ul> </li> </ol> <p><strong>常见误区：</strong></p> <ul> <li> <strong>赋值运算符<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>=</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>与比较运算符<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>==</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>混淆：</strong> 这是最经典也最容易犯的错误。<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if (x = 5)</pre><div class=”contentsignin”></div></div>在Java中是编译不通过的，因为<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>=</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>是一个赋值操作，它的结果是赋的值（<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>5</pre><div class=”contentsignin”></div></div>），而不是一个布尔值。而在C/c++中，这可能导致难以察觉的bug。Java在这里强制你使用<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>==</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>进行比较，避免了这种低级错误，我觉得这设计得很棒。<ul> <li> <strong>错误示例（Java会报错）：</strong> <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if (myVar = true)</pre><div class=”contentsignin”></div></div></li> <li> <strong>正确写法：</strong> <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if (myVar == true)</pre><div class=”contentsignin”></div></div> 或者更简洁的 <div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if (myVar)</pre><div class=”contentsignin”></div></div> (如果<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>myVar</pre><div class=”contentsignin”></div></div>本身就是布尔类型)</li> </ul> </li> <li> <strong>复杂条件缺少括号：</strong> 当布尔表达式变得复杂时，如果不使用括号明确优先级，可能会导致逻辑混乱。比如，<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>a > 10 && b < 5 || c == 0</pre><div class=”contentsignin”></div></div>，这里的优先级是<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>&&</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>高于<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>||</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>，但如果你想要先执行<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>b < 5 || c == 0</pre><div class=”contentsignin”></div></div>，就必须加括号：<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>a > 10 && (b < 5 || c == 0)</pre><div class=”contentsignin”></div></div>。养成加括号的好习惯，能让代码逻辑一目了然。</li> <li> <strong>短路与非短路运算符：</strong> <div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>&&</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>和<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>||</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>是短路运算符。这意味着如果左边的表达式已经能确定整个结果，右边的表达式就不会再计算了。例如，<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if (obj != NULL && obj.method())</pre><div class=”contentsignin”></div></div>，如果<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>obj</pre><div class=”contentsignin”></div></div>是<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>null</pre><div class=”contentsignin”></div></div>，<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>obj.method()</pre><div class=”contentsignin”></div></div>就不会被调用，从而避免了<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>NullPointerException</pre><div class=”contentsignin”></div></div>。而<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>&&lt;/pre><div class=”contentsignin”></div></div>和<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>|</pre><div class=”contentsignin”></div></div>是非短路运算符，它们会计算两边的所有表达式。在条件判断中，通常推荐使用短路运算符，因为它们更高效，并且能避免一些运行时错误。</li> </ul> <p>理解这些细节，能让你写的条件判断更加健壮和高效。</p> <h3>嵌套if语句：<a >代码可读性</a>与性能的考量</h3> <p>有时候，一个条件判断的内部，还需要基于另一个条件进行判断，这就形成了所谓的“嵌套<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>语句”。比如，我们可能需要先判断用户是否登录，如果登录了，再判断他是否有管理员权限。</p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:java;toolbar:false;’>public class NestedIfExample { public static void main(String[] args) { boolean isLoggedIn = true; String userRole = “admin”; int transactionAmount = 1500; if (isLoggedIn) { // 第一层判断：是否登录 System.out.println(“用户已登录。”); if (“admin”.equals(userRole)) { // 第二层判断：是否是管理员 System.out.println(“用户是管理员。”); if (transactionAmount > 1000) { // 第三层判断：交易金额是否过大 System.out.println(“管理员正在处理大额交易。”); // 实际业务逻辑… } else { System.out.println(“管理员正在处理常规交易。”); } } else { System.out.println(“用户是普通用户。”); if (transactionAmount > 500) { // 普通用户对金额的限制 System.out.println(“普通用户交易金额过大，需要审核。”); } else { System.out.println(“普通用户正在处理常规交易。”); } } } else { System.out.println(“用户未登录，请先登录。”); } } }</pre><div class=”contentsignin”></div></div><p>这种层层深入的结构，在逻辑上是没问题的，也确实能处理复杂的业务场景。但它有个明显的缺点，就是随着嵌套层级的增加，代码会变得越来越难以阅读和维护，俗称“箭型代码”（arrow code），因为缩进就像箭头一样往右边指。</p> <p><strong>可读性挑战：</strong> 当嵌套层级超过三层，我个人就觉得开始有点头疼了。你需要花费更多精力去追踪当前的执行路径，理解每个<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>else</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>块对应的是哪一个<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>。这不仅影响新来的开发者理解代码，对写代码的人来说，过段时间再看也可能迷茫。</p> <p><strong>性能考量：</strong> 关于性能，其实嵌套<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>本身并不会带来显著的性能问题。java编译器对这种结构有很好的优化能力。真正的性能瓶颈往往在<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>块内部执行的复杂操作，而不是<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>语句本身。所以，我们更多关注的应该是可读性和可维护性。</p> <p><strong>如何优化（扁平化处理）：</strong></p> <ul> <li> <p><strong>使用逻辑运算符合并条件：</strong> 如果多个<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>条件之间是“与”的关系，可以尝试用<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>&&</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>合并。</p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:java;toolbar:false;’>// 优化前： if (isLoggedIn) { if (“admin”.equals(userRole)) { // … } } // 优化后： if (isLoggedIn && “admin”.equals(userRole)) { // … }</pre><div class=”contentsignin”></div></div></li> <li> <p><strong>提取方法（Extract Method）：</strong> 将内部的复杂逻辑提取成单独的方法。这不仅减少了嵌套，还提高了代码的模块化程度。</p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:java;toolbar:false;’>// 优化前： if (isLoggedIn) { // 很多代码 if ("admin".equals(userRole)) { // 更多代码 } } // 优化后： if (isLoggedIn) { handleLoggedInUser(userRole, transactionAmount); } else { System.out.println("用户未登录…"); } private static void handleLoggedInUser(String userRole, int transactionAmount) { if ("admin".equals(userRole)) { // 处理管理员逻辑 } else { // 处理普通用户逻辑 } }</pre><div class=”contentsignin”></div></div></li> <li><p><strong>使用卫语句（Guard Clause）：</strong> 这种模式在下个部分会详细讲到，它通过提前返回或抛出异常来减少嵌套。</p></li> </ul> <p>所以，嵌套<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>不是洪水猛兽，但当它让代码变得难以理解时，就该考虑优化了。</p> <h3>Java条件判断的高级技巧：三元运算符与Guard Clause模式</h3> <p>除了基本的<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if-else</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>结构，Java还提供了一些更简洁或更具表达力的条件判断方式。这里我想聊聊三元运算符和卫语句（Guard Clause）模式，它们在特定场景下能让你的代码更优雅。</p> <p><strong>三元运算符 (Ternary operator)</strong></p> <p>三元运算符是<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if-else</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>语句的一种简洁形式，特别适用于根据条件给变量赋值或者返回一个值的情况。它的语法是：<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>条件 ? 表达式1 : 表达式2;</pre><div class=”contentsignin”></div></div></p> <p>如果<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>条件</pre><div class=”contentsignin”></div></div>为真，则结果是<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>表达式1</pre><div class=”contentsignin”></div></div>的值；否则，结果是<div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>表达式2</pre><div class=”contentsignin”></div></div>的值。</p><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:java;toolbar:false;’>public class TernaryOperatorExample { public static void main(String[] args) { int age = 20; String status; // 使用if-else if (age >= 18) { status = “成年人”; } else { status = “未成年人”; } System.out.println(“状态 (if-else): ” + status); // 使用三元运算符 status = (age >= 18) ? “成年人” : “未成年人”; System.out.println(“状态 (三元运算符): ” + status); int num = 10; String parity = (num % 2 == 0) ? “偶数” : “奇数”; System.out.println(num + ” 是 ” + parity); // 也可以直接用在输出语句中 System.out.println(“您有 ” + (age >= 60 ? “老年” : “青年”) + “折扣。”); } }</pre><div class=”contentsignin”></div></div><p><strong>何时使用三元运算符？</strong> 我觉得它最适合那些“二选一”的简单赋值或者作为方法参数的场景。它能让代码变得非常紧凑。</p> <p><strong>何时避免使用？</strong> 如果表达式变得复杂，或者涉及到多个操作（不仅仅是赋值），就别用三元运算符了。把多个三元运算符嵌套起来，会很快让代码变得难以理解，可读性急剧下降。这种时候，老老实实写<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if-else</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>反而更清晰。记住，代码首先是给人看的，其次才是给机器执行的。</p> <p><strong>Guard Clause (卫语句) 模式</strong></p> <p>卫语句是一种编程模式，旨在通过在方法开头处理所有异常情况或无效输入，并尽早返回或抛出异常，从而减少代码的嵌套层级，提高可读性。它的核心思想是“快速失败”（F<a >ai</a>l Fast）。</p> <p>传统的<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if-else</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>结构，往往是把主要逻辑放在<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>块里，而把异常或不符合条件的情况放在<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>else</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>里，或者在<div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=”brush:php;toolbar:false”>if</pre><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div><div class=”contentsignin”></div></div>里面继续嵌套。这样就容易出现前面提到的“箭型代码”。</p> <p>卫语句的做法是：</p> <ol> <li>检查不符合条件的情况。</li> <li>如果发现不符合，立即返回、抛出异常或执行其他终止操作。</li> <li>只有当所有前置条件都满足时，才执行方法的主体逻辑。</li> </ol><div class=”code” style=”position:relative; padding:0px; margin:0px;”><pre class=’brush:java;toolbar:false;’>public class GuardClauseExample { // 传统if-else，可能导致深层嵌套 public void processOrderTraditional(int orderId, int quantity, double price) { if (orderId > 0) { if (quantity > 0) { if (price > 0) { // 核心业务逻辑：处理订单 double total = quantity * price; System.out.println(“订单 ” + orderId + ” 处理成功，总价：” + total); } else { System.out.println(“价格必须大于0。”); } } else { System.out.println(“数量必须大于0。”); } } else { System.out.println(“订单ID无效。”); } } // 使用卫语句优化 public void processOrderWithGuardClause(int orderId, int quantity, double price) { // 卫语句1：检查订单ID if (orderId <= 0) { System.out.println(“订单ID无效，无法处理。”); return; // 提前返回 } // 卫语句2：检查数量 if (quantity <= 0) { System.out.println(“数量必须大于0，无法处理。”); return; // 提前返回 } // 卫语句3：检查价格 if (price <= 0) { System.out.println(“价格必须大于0，无法处理。”); return; // 提前返回 } // 所有前置条件都满足，执行核心业务逻辑 double total = quantity * price; System.out.println(“订单 ” + orderId + ” 处理成功，总价：” + total); } public static void main(String[] args) { GuardClauseExample example = new GuardClauseExample(); System.out.println(“— 传统方式 —“); example.processOrderTraditional(101, 5, 10.0); example.processOrderTraditional(0, 5, 10.0); example.processOrderTraditional(102, 0, 10.0); System.out.println(“n— 卫语句方式 —“); example.processOrderWithGuardClause(103, 5, 10.0); example.processOrderWithGuardClause(0, 5, 10.0); example.processOrderWithGuardClause(104, 0, 10.0); } }</pre><div class=”contentsignin”></div></div><p><strong>卫语句的优点：</strong></p> <ul> <li> <strong>提高可读性：</strong> 代码不再深层嵌套，而是从上到下线性展开。一眼就能看出哪些是异常情况，哪些是正常流程。</li> <li> <strong>简化逻辑：</strong> 每个条件判断只关注一个特定问题，逻辑更清晰。</li> <li> <strong>易于维护：</strong> 当需要添加新的校验规则时，只需在方法开头添加一个新的卫语句即可，不会影响到核心逻辑的结构。</li> </ul> <p>在我看来，卫语句是编写清晰、简洁代码的一个非常实用的技巧，尤其是在处理方法参数校验和各种前置条件时。它能让你的代码“呼吸”起来，不再那么憋屈。</p>
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