“loop:” in Java code. What is this, and why does it compile?

Question

This code just made me stare at my screen for a few minutes:

loop:
for (;;) {
    // ...
}

(line 137 here)

I have never seen this b

Answer 1

That's not a keyword, it's a label. It's meant to be used with the break and continue keywords inside nested loops:

outer:
for(;;){
    inner:
    for(;;){
        if(){
            break inner; // ends inner loop
        } else {
            break outer; // ends outer loop
        }
    }
}