📄 13.htm
字号:
<html><!-- #BeginTemplate "/Templates/empolder_doc.dwt" -->
<head>
<!-- #BeginEditable "doctitle" -->
<title>|><| 太平洋电脑信息网 -> 网络学院 -> 开发教室</title>
<!-- #EndEditable -->
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<style type="text/css">
<!--
-->
</style>
<link rel="stylesheet" href="/pcedu/style/text.css"></head>
<body bgcolor="#FFFFFF" topmargin=0 leftmargin=0 marginheight="0">
<script language="JavaScript" src="/pcedu/script/top.js">
</script>
<table width=760 border=0 cellspacing=0 cellpadding=0 align=center>
<tr>
<td width=194 height="56"><a href=http://www.pconline.com.cn><img src=http://www.pconline.com.cn/images/pconlinelogo.gif width=162 height=35 vspace=10 border=0></a></td>
<td width=406 height="56">
<script language="JavaScript" src="/pcedu/script/empolder_ad.js">
</script>
</td>
<td width=158 align=right height="56">
<script language="JavaScript" src="/pcedu/script/empolder_ad1.js">
</script>
</td>
<td align=right width=2 height="56"> </td>
</tr>
</table>
<table border=0 cellpadding=0 cellspacing=0 width=760 align="center">
<tbody>
<tr valign=bottom>
<td rowspan=2 width=172><img height=32 src="/pcedu/images/pcedu_lo.gif"
width=172 border="0"></td>
<td height=30 rowspan=2>
<table cellpadding=0 cellspacing=0 width="588" bgcolor="#FFA000" background="/pcedu/images/e_menu5.gif" border="0">
<tbody>
<tr valign="bottom">
<td height="17">
<script language="JavaScript" src="/pcedu/script/title_empolder.js">
</script>
</td>
</tr>
</tbody>
</table>
</td>
</tr>
<tr></tr>
<tr bgcolor="#303880">
<td colspan=2 height=1 valign=bottom><img height=1
src="/pcedu/images/blank.gif" width=1></td>
</tr>
<tr>
<td colspan=2 height=5 valign=bottom><img height=5
src="/pcedu/images/blank.gif" width=1></td>
</tr>
</tbody>
</table>
<table width="760" cellspacing="0" cellpadding="0" align="center" height="37">
<tr>
<td width="170" valign="top">
<table border="0" width="170" height="100%"
cellspacing="1" bgcolor="#000000">
<tr bgcolor="#F8F8D2">
<td width="100%" valign="top"><!-- #BeginEditable "left" -->
<div align="center">
<table width="100%" border="0" cellspacing="1" cellpadding="0" bgcolor="#000000" align="center">
<tr bgcolor="#E17329">
<td height="20" align="center"><font color="#FFFFFF">==<b>开发教室==</b></font></td>
</tr>
</table>
<br>
</div>
<!-- #EndEditable -->
<script language="JavaScript" src="/pcedu/script/left_empolder.js">
</script>
</td>
</tr>
</table>
</td>
<td width="10"><img src="/pcedu/images/blank.gif" width="1" height="1"></td>
<td width="580" valign="top" class="article">
<p><img src="/pcedu/images/666666.gif" width="99%" height="1"></p>
<!-- #BeginEditable "content" -->
<center>
<div align="center">
<center>
</center>
<p align="center" class="title">Java Applet 入门</p>
<p align="right"><a href="mailto:yy435@263.net">yy435</a></p>
<p align="right">太平洋网络学院</p>
</div>
<p align="center" class="green">第二天</p>
<div align="left" class="green">3、表达式与运算符</div>
<p align="JUSTIFY">表达式是由变量、常量、对象、方法调用和操作符组成的式子。符合语法规则的表达式才能被编译系统理解、执行并计算。</p>
<p align="JUSTIFY">说起表达式，也并不是很复杂，就是日常我们见到的数学式子，但有一些区别，Java中的表达式由于操作符的不同，而有很多的种类了。大致可以分为：</p>
<p align="JUSTIFY">1)赋值与强制类型转换<br>
赋值运算符对应了赋值云选，即赋予程序里的变量或对象一定的内容。简单的赋值运算是把一个表达式的值直接赋给一个变量或对象，使用的赋值运算符是“=”，格式为：<br>
变量或对象=表达式；<br>
其中赋值号右边的表达式可以是常量、另外一个变量或对象以及方法的返回值。下面给大家举几个例子：<br>
i=0;<br>
j=i;<br>
k=i+j*4;</p>
<p align="JUSTIFY">2)算术运算<font size="3"> <br>
算术运算是针对数值类型操作数进行的运算，算术运算符根据操作数字个数的不同，又可以分为：</font></p>
<p align="JUSTIFY"><font size="3"> 1.双目运算符 <br>
</font></p>
<table width="570" border="1" bordercolor="#FF9999">
<tr>
<td width="143">
<div align="center">运算符</div>
</td>
<td width="143">
<div align="center">运算</div>
</td>
<td width="93">
<div align="center">例子</div>
</td>
<td width="193">
<div align="center">解释</div>
</td>
</tr>
<tr>
<td width="143">
<div align="center">+</div>
</td>
<td width="143">
<div align="center">加</div>
</td>
<td width="93">
<div align="center">a+b</div>
</td>
<td width="193">
<div align="center">求a与b相加的和</div>
</td>
</tr>
<tr>
<td width="143">
<div align="center">-</div>
</td>
<td width="143">
<div align="center">减</div>
</td>
<td width="93">
<div align="center">a-b</div>
</td>
<td width="193">
<div align="center">求a与b相减的差</div>
</td>
</tr>
<tr>
<td width="143">
<div align="center">*</div>
</td>
<td width="143">
<div align="center">乘</div>
</td>
<td width="93">
<div align="center">a*b</div>
</td>
<td width="193">
<div align="center">求a与b相乘的积</div>
</td>
</tr>
<tr>
<td width="143">
<div align="center">/</div>
</td>
<td width="143">
<div align="center">除</div>
</td>
<td width="93">
<div align="center">a/b</div>
</td>
<td width="193">
<div align="center">求a除以b的商</div>
</td>
</tr>
<tr>
<td width="143">
<div align="center">%</div>
</td>
<td width="143">
<div align="center">取余数</div>
</td>
<td width="93">
<div align="center">a%b</div>
</td>
<td width="193">
<div align="center">求a除以b所得的余数</div>
</td>
</tr>
</table>
<p align="JUSTIFY"><font color="#FFFFFF"> 2.单目运算符</font></p>
<table width="570" border="1" bordercolor="#FF9999">
<tr>
<td width="143">
<div align="center">运算符</div>
</td>
<td width="143">
<div align="center">运算</div>
</td>
<td width="93">
<div align="center">例子</div>
</td>
<td width="193">
<div align="center">功能等价于</div>
</td>
</tr>
<tr>
<td>++</td>
<td>自增</td>
<td>a++或++a</td>
<td>a=a+1</td>
</tr>
<tr>
<td>--</td>
<td>自减</td>
<td>a--或--a</td>
<td>a=a-1</td>
</tr>
<tr>
<td>-</td>
<td>求相反数</td>
<td>-a</td>
<td>a=-a</td>
</tr>
</table>
<p align="JUSTIFY">给大家举个例子：<br>
int x=2;<br>
int y=(++x)*3;<br>
运行结果是x=3;y=9。</p>
<p align="JUSTIFY">再看另外的一个例子：<br>
int x=2;<br>
int y=(x++)*3;<br>
运行结果是x=3,y=6。</p>
<p align="JUSTIFY">这是为什么，因为第一个例子中，是x已经等于3后再算y，而后一个例子中，则是先用x=2算出y后，再算x，因为++符号在后面，这就是++x和x++的区别了。</p>
<p align="JUSTIFY">3)关系运算符<br>
关系运算是比较两个数据之间的大小关系的运算，常用的关系运算符号如下：</p>
<table width="570" border="1" bordercolor="#FF9999">
<tr>
<td>
<div align="center">运算符</div>
</td>
<td>
<div align="center">例子</div>
</td>
<td>
<div align="center">解释</div>
</td>
</tr>
<tr>
<td>
<div align="center">==</div>
</td>
<td>
<div align="center">a==b</div>
</td>
<td>
<div align="center">a等于b</div>
</td>
</tr>
<tr>
<td>
<div align="center">!=</div>
</td>
<td>
<div align="center">a!=b</div>
</td>
<td>
<div align="center">a不等于b</div>
</td>
</tr>
<tr>
<td>
<div align="center">></div>
</td>
<td>
<div align="center">a>b</div>
</td>
<td>
<div align="center">a大于b</div>
</td>
</tr>
<tr>
<td>
<div align="center"><</div>
</td>
<td>
<div align="center">a<b</div>
</td>
<td>
<div align="center">a小于b</div>
</td>
</tr>
<tr>
<td>
<div align="center">>=</div>
</td>
<td>
<div align="center">a>=b</div>
</td>
<td>
<div align="center">a大于等于b</div>
</td>
</tr>
<tr>
<td>
<div align="center"><=</div>
</td>
<td>
<div align="center">a<=b</div>
</td>
<td>
<div align="center">a小于等于b</div>
</td>
</tr>
</table>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -