在交换机内部打印

Question

期望的结果是打印“ i为零”，然后打印一，二，三，四..

似乎我的for循环工作正常，每次执行时i都变为5，但是我的情况都不是正确的，因此没有任何输出。我在做什么错？

public class SwitchTest {

    public static void main(String[] args) {
        int i;

        for ( i=0; i < 5; i++); {

        switch (i) {
            case 0:
                System.out.println("i is zero");
            case 1:
                System.out.println("i is one");
            case 2:
                System.out.println("i is two");
            case 3:
                System.out.println("i is three");
            case 4:
                System.out.println("i is four");
            }
        }
    }
}

Answer 1

您需要在每个Sysout之后添加break语句。

switch (i) {
           case 0:
                System.out.println("i is zero");
                break;
            case 1:
                System.out.println("i is one");
                break;
            case 2:
                System.out.println("i is two");
                break;
            case 3:
                System.out.println("i is three");
                break;
            case 4:
                System.out.println("i is four");
                break;
            default:
               //some statement here.

     }

Answer 2

没有输出任何内容，因为在您的for语句后加了分号，而Java也没有因为it's still valid syntax而抱怨。但是修复它，您会发现您的案例[[all在每次迭代中都会打印出来。这是因为，除非您用switch结束每个case语句，否则break语句将从相关案例一直执行到最底端。

switch (i) {
    case 0:
        System.out.println("i is zero");
        break; //"break" means "exit the switch block here, don't go any further"
    case 1:
        System.out.println("i is one");
        break;
    case 2:
        System.out.println("i is two");
        break;
    case 3:
        System.out.println("i is three");
        break;
    case 4:
        System.out.println("i is four");
        break; //This one is optional
}

为了获得良好的风格，您还应该包括一个default包，但这是另一回事了...]