Use of labels in programing

Question

I've seen this in java at least and I'm pretty sure it exists in other languages as well, but I'm referring to code like this

label: {
        if (someStatment) {
            break label;
        }
        if (someOtherStatemnt) {
            break label;
        }
        return a + b;
    }

or even:

int a = 0;
label: {
   for(int i=0;i<10; i++){
        if (a>100) {
            break label;
        }

        a+=1;
    }

Now I'm wondering what are the reason people use labels? It doesn't really seem like a good idea. I was just wondering if anyone had a real world scenario where this made sense to use this type of structure.

Related: http://stackoverflow.com/questions/245742/examples-of-good-gotos-in-c-or-c — Oded, Jan 17 '13 at 15:03
I've honestly read thousands of lines of java code and have never seen a label used. — Benjamin Gruenbaum, Jan 17 '13 at 15:04

David Gorsline · Answer 1 · 2013-01-17T20:39:32.847

Labelled breaks come into their own when loops and case statements are nested. Here's an example in Java, abridged, of something I wrote in the past 6 months:

Node matchingNode = null;  //this is the variable that we want to set
Iterator<Resource> relatedNodes = tag.find();
outer:
while (relatedNodes.hasNext() && matchingNode == null) {
    Node node = relatedNodes.next().adaptTo(Node.class);
    if (honorIsHideInNav && NodeUtils.isHideInNav(node)) {
        //we don't want to test this node
        continue;  //'continue outer' would be equivalent
    }
    PropertyIterator tagIds = node.getProperties("cq:tags");
    while (tagIds.hasNext()) {
        Property property = tagIds.nextProperty();
        Value values[] = property.getValues();
        for (Value value : values) {
            String id = value.getString();
            if (id.equals(tag.getTagID())) {
                matchingNode = node;  //found what we want!
                break outer;  //simply 'break' here would only exit the for-loop
            }
        }
    }
}
if (matchingNode == null) {
    //we've scanned all of relatedNodes and found no match
}

The data structures provided by the API that I was using are a little gnarly, hence the complicated nesting.

You can always set a flag to control your loop exits, but I find that judicious use of labelled breaks makes for more concise code.

Post script: Furthermore, if my code inspection team and or shop coding standards were to proscribe labels, I would gladly rewrite to be in conformance.

Use of labels in programing

1 Answers1