Using label and break in if-else statement

Question

I have this code which generates random number from an array, at a particular condition (when x and y both are equal to zero). I want the control to jump to the label. But the control never jumps to the label in any condition. I wanted to know that whether I am doing it right or not?

int[] arr = {0, 1, 2};    
Random rn = new Random();
label: {
    //some code
    if (x != 0 && y !=0) {
        //some code
    } else {
        break label;
    }
}

@Luksprog: Thanks brother for editing, but the code is actually for android, for keeping it simple I removed that code and added comments in those places. — user2044187, Feb 12 '13 at 15:26
Don't you need `||` instead of `&&` in your `if`? I.e. `if (x != 0 || y != 0)`? — sp00m, Feb 12 '13 at 15:31

score 12 · Answer 1 · edited Sep 13 '17 at 10:56

Without examining whether you should, yes, you can use labeled statements with if in Java. According to the 1.7 specification

The Identifier is declared to be the label of the immediately contained Statement. [...] identifier statement labels are used with break (§14.15) or continue (§14.16) statements appearing anywhere within the labeled statement.

It goes on (emphasis added)

If the statement is labeled by an Identifier and the contained Statement completes abruptly because of a break with the same Identifier, then the labeled statement completes normally. In all other cases of abrupt completion of the Statement, the labeled statement completes abruptly for the same reason.

So if you break an if block (remember a block is a statement), you can exit the if body. Let's test it:

public static void main(String[] args) {
    if (true) label: {
        if (args != null)
            break label;
        System.out.println("doesn't get here");
    }
    System.out.println("Outside of labeled block");
}

Output:

Outside of labeled block

note that there is no 'continue', i.e. with an if-else chain, the break will resume execution after the entire chain — AlexO, May 02 '23 at 14:23

Brian Roach · Answer 2 · 2013-02-12T15:35:25.217

3

The break statement breaks loops and does not transfer control to the label.

Using a label with break is for when you have inner and outer loops. An unlabeled break breaks the inner most loop (the one you are in) whereas a labeled break allows you to specify an outer loop.

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

Specifically the BreakWithLabelDemo

edited Feb 12 '13 at 15:35

answered Feb 12 '13 at 15:27

Brian Roach

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The linked example demonstrates how `break` is used with loops, but it doesn't say that it has to be used with loops explicitly. I don't know why all answers seem to think that. You can use a `break` in an if statement, please see my answer. – rath Sep 13 '17 at 11:01

sp00m · Accepted Answer · 2013-02-12T15:34:04.843

2

~~Try to~~ Avoid using labels. What you could do there, is:

while(true) {
    if(x == 0 && y == 0) {
        break;
    }
    // some stuff with x and y
}

edited Feb 12 '13 at 15:34

answered Feb 12 '13 at 15:28

sp00m

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OR: do { // some stuff } while (x!=0 || y!=0); then can avoid the break too. – sbk Feb 12 '13 at 15:31
+1 but I'd remove word "try" from your answer: "*Avoid* using labels" – AlexR Feb 12 '13 at 15:31
@sbk What if `x` and `y` already equal `0` before entering the loop? – sp00m Feb 12 '13 at 15:35
@sp00m Its a do-while loop, so it will execute once before evaluating the condition. – sbk Feb 12 '13 at 15:39

score 1 · Answer 4 · edited Nov 07 '18 at 22:01

1

I suggest that you use a recursive function.

public void work(){
    // some code
    if (x != 0 && y != 0) {
        //some code
    } else {
        work();
    }
}

You cannot use break without loops

edited Nov 07 '18 at 22:01

Zabuzard

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answered Feb 12 '13 at 15:39

Adeeb

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`You cannot use break without loops` ~ Not entirely accurate. You can use break with a `switch` statement. – Edward J Beckett Mar 15 '18 at 19:38

score -1 · Answer 5 · answered Feb 12 '13 at 15:27

-1

As far as I know, labels cannot be used arbitrarily around {}, you need to do them to mark a for, while or do-while loop

answered Feb 12 '13 at 15:27

Miquel

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you can label if-else statements as well: the compiler wouldn't raise errors. Of course, it would be no use since you can't "break" or "continue" them. :) – javatutorial May 24 '16 at 10:12

Using label and break in if-else statement

5 Answers5

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