Should I avoid using Java Label Statements?

Question

Today I had a coworker suggest I refactor my code to use a label statement to control flow through 2 nested for loops I had created. I\'ve never used them before because per

Answer 1

Yes, you should avoid using label unless there's a specific reason to use them (the example of it simplifying implementation of an algorithm is pertinent). In such a case I would advise adding sufficient comments or other documentation to explain the reasoning behind it so that someone doesn't come along later and mangle it out of some notion of "improving the code" or "getting rid of code smell" or some other potentially BS excuse.

I would equate this sort of question with deciding when one should or shouldn't use the ternary if. The chief rationale being that it can impede readability and unless the programmer is very careful to name things in a reasonable way then use of conventions such as labels might make things a lot worse. Suppose the example using 'nextCondition' and 'nextItem' had used 'loop1' and 'loop2' for his label names.

Personally labels are one of those features that don't make a lot of sense to me, outside of Assembly or BASIC and other similarly limited languages. Java has plenty of more conventional/regular loop and control constructs.

Answer 2

There are few occasions when you need labels and they can be confusing because they are rarely used. However if you need to use one then use one.

BTW: this compiles and runs.

class MyFirstJavaProg {  
        public static void main(String args[]) {
           http://www.javacoffeebreak.com/java101/java101.html
           System.out.println("Hello World!");
        }
}

Answer 3

I think with the new for-each loop, the label can be really clear.

For example:

sentence: for(Sentence sentence: paragraph) {
  for(String word: sentence) {
    // do something
    if(isDone()) {
      continue sentence;
    }
  }
}

I think that looks really clear by having your label the same as your variable in the new for-each. In fact, maybe Java should be evil and add implicit labels for-each variables heh

Answer 4

Many algorithms are expressed more easily if you can jump across two loops (or a loop containing a switch statement). Don't feel bad about it. On the other hand, it may indicate an overly complex solution. So stand back and look at the problem.

Some people prefer a "single entry, single exit" approach to all loops. That is to say avoiding break (and continue) and early return for loops altogether. This may result in some duplicate code.

What I would strongly avoid doing is introducing auxilary variables. Hiding control-flow within state adds to confusion.

Splitting labeled loops into two methods may well be difficult. Exceptions are probably too heavyweight. Try a single entry, single exit approach.

Answer 5

Labels are like goto's: Use them sparingly, and only when they make your code faster and more importantly, more understandable,

e.g., If you are in big loops six levels deep and you encounter a condition that makes the rest of the loop pointless to complete, there's no sense in having 6 extra trap doors in your condition statements to exit out the loop early.

Labels (and goto's) aren't evil, it's just that sometimes people use them in bad ways. Most of the time we are actually trying to write our code so it is understandable for you and the next programmer who comes along. Making it uber-fast is a secondary concern (be wary of premature optimization).

When Labels (and goto's) are misused they make the code less readable, which causes grief for you and the next developer. The compiler doesn't care.