syntax - Labeled Statement block in Java?

Question

I was browsing through some of the base Java objects when I found a section of code surrounded by a scan: {} block. The following code is from the toLowerCase() method inside the String class.

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;
        }

Could someone please explain what the scan:{} block is used for and where this syntax comes from? I've yet to see a colon after a word like this in Java unless used in a ternary operator.

Thanks!

Edit: Updated title to correctly match answered question.

Answer 1

Here, scan: is simply a label. The break <label> syntax allows one to break out of outer loops, and to simulate some forms of the goto statement. The syntax is documented in the JLS:

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.