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<div align="center" class="title">JAVA程序员必读：基础篇（3）语言基础</div>
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<div align="center"><font color="#666666">编译：ZSC/太平洋网络学院</font></div>
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<div align="right" class="gray"><a href="mailto:tntst@pconline.com.cn">［责编:爆破手］</a></div>
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<p class="article"> <b>语言基础</b> </p>
<p></p>
<p></p>
<p class="article"><b>3.4.3 if-else语句</b></p>
<p class="article"> if语句可以使程序根据一些条件有选择地执行语句。举个例子，假如你的程序根据boolean变量DEBUG的值来打印了调试信息。如果DEBUG是true，你的程序就打印出调试信息，比如变量x的数值；或者就不打印。具体的程序如下：
</p>
<p class="article">if (DEBUG) {</p>
<p class="article"> System.out.println("DEBUG: x = " + x);</p>
<p class="article">}</p>
<p class="article"> 上面是一个简单的if语句的例子。总得说来，if语句的语法格式为： </p>
<p class="article"> if (表达式) {</p>
<p class="article"> 语句（参数）</p>
<p class="article">}</p>
<p class="article"> 如果你想在if判断表达式为false的时候执行不同的语句，你可以使用else语句。举个另外的例子吧，假如你的程序需要执行不同的工作，主要是根据用户是点击OK键还是击警告窗口中的其它按钮。你可以使用if和else语句来实现这个目的：
</p>
<p class="article"> . . .</p>
<p class="article"> // response is either OK or CANCEL depending</p>
<p class="article"> // on the button that the user pressed</p>
<p class="article"> . . .</p>
<p class="article">if (response == OK) {</p>
<p class="article"> // 在这里添加执行OK动作的代码</p>
<p class="article"> } else {</p>
<p class="article"> // 在这里添加执行Cancel动作的代码</p>
<p class="article"></p>
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