（29）表達式 · Java編程那些事

## Java編程那些事兒29—表達式鄭州游戲學院陳躍峰出自：[http://blog.csdn.net/mailbomb](http://blog.csdn.net/mailbomb) **4.8 表達式** 由運算符和變量、常數或常量組成的式子稱為表達式。例如2+3,a*b等。表達式是組成程序的基本單位，也是程序運算時的基本單位。在程序代碼內部，每個表達式都有自己對應的數據類型，具體參看下表：表達式結果類型 <table style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; MARGIN-LEFT: 62.1pt; BORDER-LEFT: medium none; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse" cellspacing="0" cellpadding="0" border="1"><tbody><tr><td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: black 1pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: black 1pt solid; WIDTH: 35.45pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="47"> <div align="center">序號</div> </td> <td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: black 1pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 92.15pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="123"> <div align="center">運算符</div> </td> <td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: black 1pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 3cm; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="113"> <div align="center">結果類型</div> </td> </tr><tr><td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: black 1pt solid; WIDTH: 35.45pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" width="47" rowspan="4"> <div align="center">1</div> </td> <td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 92.15pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="123"> <div align="center">算術運算符</div> </td> <td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 3cm; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" width="113" rowspan="4"> <div align="center">數字型</div> </td> </tr><tr><td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 92.15pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="123"> <div align="center">位運算符</div> </td> </tr><tr><td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 92.15pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="123"> <div align="center">移位運算符</div> </td> </tr><tr><td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 92.15pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="123"> <div align="center">遞增、遞減運算符</div> </td> </tr><tr><td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: black 1pt solid; WIDTH: 35.45pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" width="47" rowspan="2"> <div align="center">2</div> </td> <td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 92.15pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="123"> <div align="center">比較運算符</div> </td> <td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 3cm; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" width="113" rowspan="2"> <div align="center">布爾型</div> </td> </tr><tr><td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 92.15pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="123"> <div align="center">邏輯運算符</div> </td> </tr><tr><td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: black 1pt solid; WIDTH: 35.45pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="47"> <div align="center">3</div> </td> <td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 92.15pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="123"> <div align="center">賦值運算符</div> </td> <td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 3cm; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="113"> <div align="center">和變量類型一致</div> </td> </tr><tr><td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: black 1pt solid; WIDTH: 35.45pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="47"> <div align="center">4</div> </td> <td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 92.15pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="123"> <div align="center">條件運算符</div> </td> <td style="BORDER-RIGHT: black 1pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 3cm; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="113"> <div align="center">和兩個值中類型高的一致</div> </td> </tr></tbody></table> 對于序號1和2的運算符組成的表達式，由于比較直觀，就不再單獨舉例了，對于3和4說明如下： ~~~ ?????????????????? int n = 10; ?????????????????? int m = 10; ?????????????????? n =( m = 10);?? //則表達式m=10的類型是變量m的類型，也是m的值 ?????????????????? boolean b = false; ?????????????????? boolean b1 = true; ?????????????????? b = (b1 = true);?//則表達式b1 = true的類型是布爾型，值是true ?????????????????? double d; d = 10 > 0 ? 1.0 : 2; //由于1.0是double型，2是整數型，則表達式的類型是double ~~~ 對于由多個運算符組成的表達式，其最終的類型由最后一個運算符決定。在實際的程序代碼中，大部分的表達式不能單獨成為代碼中的一行，否則程序會提示語法錯誤，例如： ~~~ ?????????????????? int a = 10; ?????????????????? int b = 20; ?????????????????? a + b;??? //不能單獨成行 ~~~ 在表達式中，能夠單獨成行的運算符包括賦值運算符和遞增、遞減運算符。 **4.9 總結** 本部分系統的講解了Java語言中運算符的知識，并且介紹了實際使用過程中需要注意的問題，在學習時需要熟記每種運算符的作用，然后在實際項目中根據需要使用對應的運算符來實現程序的功能。