Java 程式設計/關鍵字/switch

switch 是一個 Java 關鍵字。

它是一個基於數字的分支操作。該“數字”必須是 char、byte、short 或 int 原生型別。

語法

switch ( <integer-var> )
{
   case <label₁>: <statements>;
   case <label₂>: <statements>;
   ...
   case <label_n>: <statements>;
   default: <statements>;
}

當 <integer-var> 值與其中一個 <label> 匹配時，則：匹配的標籤後的語句將被執行，包括以下標籤的語句，直到 switch 塊的末尾，或直到遇到 break 關鍵字。

例如

int var = 3;
switch ( var )
{
   case 1: 
      System.out.println( "Case: 1" );
      System.out.println( "Execute until break" );
      break;		  	
   case 2: 
      System.out.println( "Case: 2" );
      System.out.println( "Execute until break" );
      break;
   case 3:
      System.out.println( "Case: 3" );
      System.out.println( "Execute until break" );
      break;  	
   case 4:
      System.out.println( "Case: 4" );
      System.out.println( "Execute until break" );
      break;      
   default:
      System.out.println( "Case: default" );
      System.out.println( "Execute until break" );
      break;	      
}

以上程式碼的輸出為

Case: 3
Execute until break

相同的程式碼可以用 if-else 塊編寫"

int var = 3;
if ( var == 1 ) {
   System.out.println( "Case: 1" );
   System.out.println( "Execute until break" );
} else if ( var == 2 ) {
   System.out.println( "Case: 2" );
   System.out.println( "Execute until break" );
} else if ( var == 3 ) {
   System.out.println( "Case: 3" );
   System.out.println( "Execute until break" );
} else if ( var == 4 ) {
   System.out.println( "Case: 4" );
   System.out.println( "Execute until break" );
} else {
   // -- This is the default part -- 
   System.out.println( "Case: default" );
   System.out.println( "Execute until break" );
}

另請參見

Java 程式設計/關鍵字/if