java - 无法在 Java 中获取 Switch 案例的行为

Question

我用java 6写过小代码

public class TestSwitch{

public static void main(String... args){
    int a = 1;
    System.out.println("start");
    switch(a){
        case 1:{
            System.out.println(1);
            case 3:
                System.out.println(3);
            case 4:
                System.out.println(4);
        }
        case 2:{
            System.out.println(2);
            case 5:
                System.out.println(5);
            case 7:
                System.out.println(7);
        }
            
    }
    System.out.println("end");
}
}

Output: start 1 2 end

我的编辑器正在显示“案例 3”和“案例 5”的孤立案例。它仍在运行 并显示输出。

• Java 中有类似概念的 Nastated cases 吗？

• 为什么它会给出以上输出？相反，我认为它将是“开始 1 结束”

  非常感谢您的回复!!

Answer 1

Switch 替换 if else 但 switch 语法 != If else 语法。

你忘了在每个 case 后面加上 break。

所以条件落空了。

示例:

case 0:
          mColor.setText("#000000");
          break;

You can find that in docs

The break statements are necessary because without them, statements in switch blocks fall through: All statements after the matching case label are executed in sequence, regardless of the expression of subsequent case labels, until a break statement is encountered.

public static void main(String... args){
        int a = 1;
        System.out.println("start");
        switch(a){
            case 1: 
                System.out.println(1);
                break;
            case 2:
                  System.out.println(2);
                  break;
            case 3:
                System.out.println(3);
                break;
            case 4:
                System.out.println(4);
                break;
            case 5:
                System.out.println(5);
                break;
            case 7:
                System.out.println(7);
                break;
            default:
                System.out.println("nothing");

            }