java - 使用枚举切换大小写会导致重复

Question

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已关闭 10 年前。

当我使用 for-each 循环和 switch 语句迭代一个简单的枚举测试器来输出枚举值时，我看到了对我来说似乎很奇怪的行为。

代码:

public class EnumTest {

    private Number number;

    public EnumTest(Number number) {
        this.number = number;
    }
    public enum Number {
        ONE,
        TWO,
        THREE,
        FOUR,
        FIVE;
    }
    private void tellItLikeItIs() { 
        switch (number) {   
            case ONE:
                System.out.println("ONE");
            case TWO:
                System.out.println("TWO");
            case THREE:
                System.out.println("THREE");
            case FOUR:
                System.out.println("FOUR");
            case FIVE:
                System.out.println("FIVE"); 
        }
    }
    public static void main(String[] args) {    
        for (Number n : Number.values()) {
            EnumTest et = new EnumTest(n);
            et.tellItLikeItIs();
            System.out.println();
        }
    }
}

输出:

    ONE
    TWO
    THREE
    FOUR
    FIVE

    TWO
    THREE
    FOUR
    FIVE

    THREE
    FOUR
    FIVE

    FOUR
    FIVE

    FIVE

为什么每次调用都会返回自身以及所有后续值？

Answer 1

那是因为你忘记了 break; 语句...

private void tellItLikeItIs() { 
        switch (number) {   
            case ONE:
                System.out.println("ONE");
                break;
            case TWO:
                System.out.println("TWO");
                break;
            case THREE:
                System.out.println("THREE");
                break;
            case FOUR:
                System.out.println("FOUR");
                break;
            case FIVE:
                System.out.println("FIVE"); 
                break;
        }
    }

了解有关 switch 语句的更多信息 here :

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