Java - 标签(label)

在Java中, 标签必须在循环之前使用, 一个循环之中嵌套另一个循环的开关, 从多重嵌套中continue或break.
控制循环:
1. continue会退回最内层的循环开头, 并继续执行;
2. 带标签的continue会到达标签的位置, 重新进入标签下面的循环;
3. break会中断并跳出当前循环;
4. 带标签的break会中断跳出标签下面的循环.

for循环的标签示例

//: Main.java

/**
 * for循环标签
 */
class Main {
    public static void main(String[] args) {
        int i=0;
        outer:
        for (;true;) {
            inner:
            for (; i<10; i++) {
                System.out.println("i = " + i);
                if (i==2) {
                    System.out.println("continue");
                    continue;
                }
                if (i==3) {
                    System.out.println("break");
                    ++i;
                    break;
                }
                if (i==7) {
                    System.out.println("continue outer");
                    i++;
                    continue outer;
                }
                if (i==8) {
                    System.out.println("break outer");
                    break outer;
                }
                for (int k=0; k<5; k++) {
                    if (k==3) {
                        System.out.println("continue inner");
                        continue inner;
                    }
                }
            }
        }
    }
}
/**
 * Output:
 i = 0
 continue inner
 i = 1
 continue inner
 i = 2
 continue
 i = 3
 break
 i = 4
 continue inner
 i = 5
 continue inner
 i = 6
 continue inner
 i = 7
 continue outer
 i = 8
 break outer
 *///:~

while循环的标签示例

//: Main.java

/**
 * while循环标签
 */
class Main {
    public static void main(String[] args) {
        int i=0;
        outer:
        while (true) {
            System.out.println("Outer while loop");
            while (true) {
                i++;
                System.out.println("i = " + i);
                if (i == 1) {
                    System.out.println("continue");
                    continue;
                }
                if (i == 3) {
                    System.out.println("continue outer");
                    continue outer;
                }
                if (i == 5) {
                    System.out.println("break");
                    break;
                }
                if (i == 7) {
                    System.out.println("break outer");
                    break outer;
                }
            }
        }
    }
}
/**
 * Output:
 Outer while loop
 i = 1
 continue
 i = 2
 i = 3
 continue outer
 Outer while loop
 i = 4
 i = 5
 break
 Outer while loop
 i = 6
 i = 7
 break outer
 *///:~