java - Java 中的标记语句 block ？

Question

当我发现一段代码被 scan:{} block 包围时，我正在浏览一些基本的 Java 对象。以下代码来自 String 类中的 toLowerCase() 方法。

scan: {
            for (firstUpper = 0 ; firstUpper < len; ) {
                char c = value[firstUpper];
                if ((c >= Character.MIN_HIGH_SURROGATE)
                        && (c <= Character.MAX_HIGH_SURROGATE)) {
                    int supplChar = codePointAt(firstUpper);
                    if (supplChar != Character.toLowerCase(supplChar)) {
                        break scan;
                    }
                    firstUpper += Character.charCount(supplChar);
                } else {
                    if (c != Character.toLowerCase(c)) {
                        break scan;
                    }
                    firstUpper++;
                }
            }
            return this;
        }

有人可以解释一下 scan:{} block 的用途以及此语法的来源吗？除非在三元运算符中使用，否则我还没有在 Java 中看到像这样的单词后有冒号。

谢谢!

编辑:更新标题以正确匹配已回答的问题。

Answer 1

在这里，scan:只是一个label . break <label>语法允许跳出外部循环，并模拟某些形式的 goto陈述。语法记录在 JLS 中:

A break statement with label Identifier attempts to transfer control to the enclosing labeled statement (§14.7) that has the same Identifier as its label; this statement, which is called the break target, then immediately completes normally. In this case, the break target need not be a switch, while, do, or for statement.