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<title>|><| 太平洋電腦信息網 -> 網絡學院 -> 開發教室</title>
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<td height="20" align="center"><font color="#FFFFFF">==<b>開發教室==</b></font></td>
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<p align="center" class="title">Java Applet 入門</p>
<p align="right"><a href="mailto:yy435@263.net">yy435</a></p>
<p align="right">太平洋網絡學院</p>
</div>
<p align="center" class="green">第二天</p>
<div align="left" class="green">3、表達式與運算符</div>
<p align="JUSTIFY">表達式是由變量、常量、對象、方法調用和操作符組成的式子。符合語法規則的表達式才能被編譯系統理解、執行并計算。</p>
<p align="JUSTIFY">說起表達式，也并不是很復雜，就是日常我們見到的數學式子，但有一些區別，Java中的表達式由于操作符的不同，而有很多的種類了。大致可以分為：</p>
<p align="JUSTIFY">1)賦值與強制類型轉換<br>
賦值運算符對應了賦值云選，即賦予程序里的變量或對象一定的內容。簡單的賦值運算是把一個表達式的值直接賦給一個變量或對象，使用的賦值運算符是“=”，格式為：<br>
變量或對象=表達式；<br>
其中賦值號右邊的表達式可以是常量、另外一個變量或對象以及方法的返回值。下面給大家舉幾個例子：<br>
i=0;<br>
j=i;<br>
k=i+j*4;</p>
<p align="JUSTIFY">2)算術運算<font size="3"> <br>
算術運算是針對數值類型操作數進行的運算，算術運算符根據操作數字個數的不同，又可以分為：</font></p>
<p align="JUSTIFY"><font size="3"> 1.雙目運算符 <br>
</font></p>
<table width="570" border="1" bordercolor="#FF9999">
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<td width="143">
<div align="center">運算符</div>
</td>
<td width="143">
<div align="center">運算</div>
</td>
<td width="93">
<div align="center">例子</div>
</td>
<td width="193">
<div align="center">解釋</div>
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<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與b相加的和</div>
</td>
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<td width="143">
<div align="center">-</div>
</td>
<td width="143">
<div align="center">減</div>
</td>
<td width="93">
<div align="center">a-b</div>
</td>
<td width="193">
<div align="center">求a與b相減的差</div>
</td>
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<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與b相乘的積</div>
</td>
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<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>
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<td width="143">
<div align="center">%</div>
</td>
<td width="143">
<div align="center">取余數</div>
</td>
<td width="93">
<div align="center">a%b</div>
</td>
<td width="193">
<div align="center">求a除以b所得的余數</div>
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<p align="JUSTIFY"><font color="#FFFFFF"> 2.單目運算符</font></p>
<table width="570" border="1" bordercolor="#FF9999">
<tr>
<td width="143">
<div align="center">運算符</div>
</td>
<td width="143">
<div align="center">運算</div>
</td>
<td width="93">
<div align="center">例子</div>
</td>
<td width="193">
<div align="center">功能等價于</div>
</td>
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<tr>
<td>++</td>
<td>自增</td>
<td>a++或++a</td>
<td>a=a+1</td>
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<tr>
<td>--</td>
<td>自減</td>
<td>a--或--a</td>
<td>a=a-1</td>
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<td>-</td>
<td>求相反數</td>
<td>-a</td>
<td>a=-a</td>
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<p align="JUSTIFY">給大家舉個例子：<br>
int x=2;<br>
int y=(++x)*3;<br>
運行結果是x=3;y=9。</p>
<p align="JUSTIFY">再看另外的一個例子：<br>
int x=2;<br>
int y=(x++)*3;<br>
運行結果是x=3,y=6。</p>
<p align="JUSTIFY">這是為什么，因為第一個例子中，是x已經等于3后再算y，而后一個例子中，則是先用x=2算出y后，再算x，因為++符號在后面，這就是++x和x++的區別了。</p>
<p align="JUSTIFY">3)關系運算符<br>
關系運算是比較兩個數據之間的大小關系的運算，常用的關系運算符號如下：</p>
<table width="570" border="1" bordercolor="#FF9999">
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<td>
<div align="center">運算符</div>
</td>
<td>
<div align="center">例子</div>
</td>
<td>
<div align="center">解釋</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>
<p align="JUSTIFY">關系運算符的結果是步爾值，也就是只有“真”和假兩種答案，例如：<br>
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