（22）比較運算符 · Java編程那些事

## Java編程那些事兒22—比較運算符鄭州游戲學院陳躍峰出自：[http://blog.csdn.net/mailbomb](http://blog.csdn.net/mailbomb) **4.2 比較運算符** 比較運算符實現數據之間大小或相等的比較。比較運算符運算的結果是一個boolean類型的值，如果比較結果成立則為true，否則為false。 Java語言中比較運算符的表示和功能見下表4-2。表4-2 比較運算符 <table style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; MARGIN-LEFT: -3.95pt; 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: 33.75pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="45"> <div align="center">符號</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: 55.25pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="74"> <div align="center">名稱</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: 190.6pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="254"> <div align="center">功能說明</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: 33.75pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="45"> <div align="center">>?</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: 55.25pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="74"> <div align="center">大于</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: 190.6pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="254"> <div align="center">比較左側數字是否大于右側數字</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: 33.75pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="45"> <div align="center"><?</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: 55.25pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="74"> <div align="center">小于</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: 190.6pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="254"> <div align="center">比較左側數字是否小于右側數字</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: 33.75pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="45"> <div align="center">>=</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: 55.25pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="74"> <div align="center">大于等于</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: 190.6pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="254"> <div align="center">比較左側數字是否大于或等于右側數字</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: 33.75pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="45"> <div align="center"><=</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: 55.25pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="74"> <div align="center">小于等于</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: 190.6pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="254"> <div align="center">比較左側數字是否小于或等于右側數字</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: 33.75pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="45"> <div align="center">==</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: 55.25pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="74"> <div align="center">等于</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: 190.6pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="254"> <div align="center">比較左側數字是否等于右側數字</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: 33.75pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="45"> <div align="center">!=</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: 55.25pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="74"> <div align="center">不等于</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: 190.6pt; PADDING-TOP: 0cm; BORDER-BOTTOM: black 1pt solid" valign="top" width="254"> <div align="center">比較左側數字是否不等于右側數字</div> </td> </tr></tbody></table> 比較運算符的運算規則和現實中的規則一樣。需要注意的問題主要有以下幾個： 1.?boolean類型只能比較相等和不相等，不能比較大小。 2.?>=的意思是大于或等于，兩者成立一個即可，所以5>=5成立。 3.?在數學上表示的區間[1,10)，也就是數字大于等于1同時小于10，在程序中不能寫成如下格式：1<=n<10，這種書寫在語法上是錯誤的，如果需要表達這種區間，則參看4.3邏輯運算符實現部分。 4.?判斷相等的符號是兩個等號，而不是一個等號，這個需要特別小心。比較運算使用的示例代碼如下： ~~~ ???????? int a = 10; ???????? boolean b = (a > 3);?//該條件成立，則將值true賦值給變量b ???????? boolean c = (b == true);?//條件成立，結果為true ~~~ 在實際代碼中，數值、變量以及運算結果都可以直接參與比較，只是程序中為了增強可讀性，有些時候需要將比較分開進行書寫。比較運算符是程序設計中實現數據比較的基礎，也是很多邏輯實現的基礎，在程序邏輯中，經常通過比較一定的條件，來判斷后續的程序該如何執行。