How do I break from the main/outer loop in a double/nested loop? [duplicate]

Question

If I have loop in a loop and once an if statement is satisfied I want to break main loop, how am I supposed to do that?

This is my code:

for (int d = 0; d < amountOfNeighbors; d++) {
    for (int c = 0; c < myArray.size(); c++) {
        if (graph.isEdge(listOfNeighbors.get(d), c)) {
            if (keyFromValue(c).equals(goalWord)) { // Once this is true I want to break main loop.
                System.out.println("We got to GOAL! It is "+ keyFromValue(c));
                break; // This breaks the second loop, not the main one.
            }
        }
    }
}

use a label. docs.oracle.com/javase/tutorial/java/nutsandbolts/branch.html — Colin D
– Colin D, Commented Oct 25, 2012 at 16:44

Peter Mortensen · Accepted Answer · 2019-01-05 09:40:21Z

61

Using a labeled break:

mainloop:
for(){
 for(){
   if (some condition){
     break mainloop;
   }
  }
}

Also See

edited Jan 5, 2019 at 9:40

Peter Mortensen

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answered Oct 25, 2012 at 16:44

Jigar Joshi

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2 Comments

ADTC Over a year ago

Awesome! I learnt something new. I thought labels were for days gone by (remember GW-BASIC?). I would have used boolean flags for this, but labels are much cooler!

user Over a year ago

@ADTC GW-BASIC never supported textual labels, only numerical line numbers (and it required those). IIRC, coming out of Microsoft it was QuickBASIC that added support for textual labels, as well as named subroutines. QBasic certainly included such support if Wikipedia is to be trusted, at least no later than Visual Basic.

Peter Mortensen · Accepted Answer · 2019-01-05 09:41:56Z

28

You can add labels to your loop, and use that labelled break to break out of the appropriate loop: -

outer: for (...) {
    inner: for(...) {
        if (someCondition) {
            break outer;
        }
    }
}

See these links for more information:

edited Jan 5, 2019 at 9:41

Peter Mortensen

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answered Oct 25, 2012 at 16:44

Rohit Jain

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Comments

Peter Mortensen · Accepted Answer · 2019-01-05 09:43:26Z

12

You can just return the control from that function. Or use the ugly break labels approach :)

If there is another code parts after your for statement, you can refactor the loops in a function.

IMO, the use of breaks and continue should be discouraged in OOP, since they affect the readability and the maintenance. Sure, there are cases where they are handy, but in general I think that we should avoid them, since they will encourage the use of goto style programing.

Apparently variations to this questions are posted a lot. Here Peter provided some good and odd uses using labels.

edited Jan 5, 2019 at 9:43

Peter Mortensen

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answered Oct 25, 2012 at 16:45

dan

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9 Comments

John Dvorak Over a year ago

Source/defend your claim that labels are ugly

Colin D Over a year ago

In this particular case, return may be appropriate. However labels are not ugly and often useful.

dan Over a year ago

@JanDvorak Thanks, ugly and hard to debug.

user166390 Over a year ago

(I generally find some languages unbearably hard to read for other reasons - I can't even recall the last time I used explicit "double loops" that required breaking in a language that had proper HoF support and a supportive collection APIs. This would be much more cleanly written in terms of an "Any" function, IMOHO ;-)

Bhesh Gurung Over a year ago

IMO, it's good to rethink about how to write the code again to avoid labled loops. The reason why so many people don't know that they exist is because we don't need them. I am not saying they are always bad.

|

Peter Mortensen · Accepted Answer · 2019-01-05 09:47:12Z

3

It looks like for Java a labeled break appears to be the way to go (based on the consensus of the other answers).

But for many (most?) other languages, or if you want to avoid any goto like control flow, you need to set a flag:

bool breakMainLoop = false;
for(){
    for(){
        if (some condition){
            breakMainLoop = true;
            break;
        }
    }
    if (breakMainLoop) break;
}

edited Jan 5, 2019 at 9:47

Peter Mortensen

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answered Oct 25, 2012 at 20:55

Thymine

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3 Comments

Evan Harper Over a year ago

If a labelled break really is the way to go in Java, then the way to go in C/C++ is a goto.

user Over a year ago

Also, the question is clearly labelled as java.

Thymine Over a year ago

Doesn't change the fact that someone searching for 'break nested loop' might come upon it. @EvanHarper I would agree with that line of reasoning, but I haven't spent much time in Java so just went with the consensus of the other answers...

Peter Mortensen · Accepted Answer · 2019-01-05 09:44:14Z

2

Just for fun:

for(int d = 0; d < amountOfNeighbors; d++){
    for(int c = 0; c < myArray.size(); c++){
        ...
            d = amountOfNeighbors;
            break;
        ...
    }
    // No code here
}

Comment on break label : it's a forward goto. It can break any statement and jump to the next:

foo: // Label the next statement (the block)
{
    code ...
    break foo;  // goto [1]
    code ...
}

//[1]

edited Jan 5, 2019 at 9:44

Peter Mortensen

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answered Oct 25, 2012 at 16:54

irreputable

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3 Comments

John Dvorak Over a year ago

Syntax error. Missing a semicolon.

Rohit Jain Over a year ago

haha :) Will sure upvote for this creative thinking

John Dvorak Over a year ago

I hope noone ever uses this in production :-)

Peter Mortensen · Accepted Answer · 2019-01-05 09:48:53Z

0

The best and easy methods for beginners even:

outerloop:

for(int i=0; i<10; i++){

    // Here we can break the outer loop by:
    break outerloop;

    innerloop:

    for(int i=0; i<10; i++){

        // Here we can break innerloop by:
        break innerloop;
    }
}

edited Jan 5, 2019 at 9:48

Peter Mortensen

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answered Aug 23, 2015 at 21:10

Keshav bansal

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