Java关于scan,break scan

看源码的时候，看到了新的语法，scan，break  scan。

下面源码摘抄于String.class的toUpperCase(Locale locale)方法

/* Now check if there are any characters that need to be changed. */
scan: {
    for (firstLower = 0 ; firstLower < len; ) {
        int c = (int)value[firstLower];
        int srcCount;
        if ((c >= Character.MIN_HIGH_SURROGATE)
                && (c <= Character.MAX_HIGH_SURROGATE)) {
            c = codePointAt(firstLower);
            srcCount = Character.charCount(c);
        } else {
            srcCount = 1;
        }
        int upperCaseChar = Character.toUpperCaseEx(c);
        if ((upperCaseChar == Character.ERROR)
                || (c != upperCaseChar)) {
            break scan;
        }
        firstLower += srcCount;
    }
    return this;
}

这语法是用来跳出多重循环的，'scan' 是自定义的，例子如下：

System.out.println("START");
a: {
    for (int i = 0; i < 10; i++ ) {
        System.out.println("START-" + i + "---------------");
        for (int j = 0; j < 10; j++) {
            System.out.println(j);
            if (j == 3) {
                break a;
            }
        }
        System.out.println("END-" + i + "---------------");
    }
}
System.out.println("END");

输出如下：

START
START-0---------------
0
1
2
3
END

可以尝试把break a;改成break;看看输出结果。