Is using a labeled break a good practice in Java?

Question

I'm staring at some old code from 2001 and came across this statement:

   else {      do {        int c = XMLDocumentFragmentScannerImpl.this.scanContent();        if (c == 60) {          XMLDocumentFragmentScannerImpl.this.fEntityScanner.scanChar();          XMLDocumentFragmentScannerImpl.this.setScannerState(1);          break label913;        } 

I had never seeen this before, and discovered labeled breaks here:

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/branch.html

Doesn't this essentially function like goto? Is it even good practice to use it? It makes me uneasy.

Answer 1

No, it's not like a goto, since you can't "go" to another part of the control flow.

From the page you linked:

The break statement terminates the labeled statement; it does not transfer the flow of control to the label. Control flow is transferred to the statement immediately following the labeled (terminated) statement.

This means you can only break loops that are currently being executed.

Consider this example:

first: for( int i = 0; i < 10; i++) {   second:   for(int j = 0; j < 5; j ++ )   {     break xxx;   } }  third: for( int a = 0; a < 10; a++) {  } 

You could replace xxx with first or second (to break the outer or inner loop), since both loops are being executed, when you hit the break statement, but replacing xxx with third won't compile.

Answer 2

It's not as terrible as goto because it only sends control to the end of the labeled statement (typically a loop construct). The thing that makes goto unlikeable is that it is an arbitrary branch to anywhere, including labels found higher up in the method source, so that you can have home-grown looping behavior. The label-break functionality in Java doesn't allow that kind of craziness because control only goes forward.

I've only used it once about 12 years ago, in a situation where I was needing to break out of nested loops, the more-structured alternative would've made for more complicated tests in the loops. I wouldn't advise using it a lot but I wouldn't flag it as an automatic bad-code smell.