What does the return keyword do in a void method in Java?

Question

I'm looking at a path finding tutorial and I noticed a return statement inside a void method (class PathTest, line 126):

if ((x < 0) || (y < 0) || (x >= map.getWidthInTiles()) || (y >= map.getHeightInTiles())) {
    return;
}

I'm a novice at Java. Can anyone tell me why it's there? As far as I knew, return inside a void method isn't allowed.

score 139 · Accepted Answer · edited Jun 29 '15 at 20:21

139

It just exits the method at that point. Once return is executed, the rest of the code won't be executed.

eg.

public void test(int n) {
    if (n == 1) {
        return; 
    }
    else if (n == 2) {
        doStuff();
        return;
    }
    doOtherStuff();
}

Note that the compiler is smart enough to tell you some code cannot be reached:

if (n == 3) {
    return;
    youWillGetAnError(); //compiler error here
}

edited Jun 29 '15 at 20:21

Ian R. O'Brien

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answered Apr 13 '09 at 17:30

CookieOfFortune

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I understand your code is illustrative, but for the parent's info; I've worked with people that believe each method should only have a single return statement. I'm not one of them, but do believe in minimizing the number of returns as much as possible without making the code ugly in doing it. – digitaljoel Apr 13 '09 at 18:51
3

Yeah, it's definitely not something to overuse, but sometimes it just makes it a lot easier and can still be very readable. – CookieOfFortune Apr 13 '09 at 19:40
5

My favorite way of breaking from nested loops :) – b1nary.atr0phy May 13 '13 at 22:10
2

Without a return value `return` works a lot like `break` in a loop and simply exits the code in question. There have been many flame wars about multiple exit points from functions and a few languages force you one way or the other. I don't take a position on multiple exit points, but I will point out that leaving a function cleans up the local stack. – Michael Shopsin Nov 11 '14 at 15:11

score 28 · Answer 2 · edited Nov 22 '14 at 11:07

You can have return in a void method, you just can't return any value (as in return 5;), that's why they call it a void method. Some people always explicitly end void methods with a return statement, but it's not mandatory. It can be used to leave a function early, though:

void someFunct(int arg)
{
    if (arg == 0)
    {
        //Leave because this is a bad value
        return;
    }
    //Otherwise, do something
}

score 23 · Answer 3 · answered Apr 13 '09 at 17:36

23

The keyword simply pops a frame from the call stack returning the control to the line following the function call.

answered Apr 13 '09 at 17:36

MahdeTo

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Haha. This is great answer but I doubt beginners in java would really grasp what you're trying to say. – franklin Jan 04 '13 at 14:19
@ElliotMok Fair enough. We all start out as beginners! – franklin Dec 13 '18 at 22:27
Is this a good practice or doesn't matter whether we write `return;` or not? – Hamza Khan Feb 24 '21 at 06:08

score 13 · Answer 4 · answered Apr 13 '09 at 17:32

13

The Java language specification says you can have return with no expression if your method returns void.

answered Apr 13 '09 at 17:32

John Ellinwood

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score 3 · Answer 5 · answered Apr 13 '09 at 17:33

3

It exits the function and returns nothing.

Something like return 1; would be incorrect since it returns integer 1.

answered Apr 13 '09 at 17:33

Albert

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score 2 · Answer 6 · answered Apr 13 '09 at 17:33

2

It functions the same as a return for function with a specified parameter, except it returns nothing, as there is nothing to return and control is passed back to the calling method.

answered Apr 13 '09 at 17:33

Chris Ballance

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score 1 · Answer 7 · edited Oct 20 '16 at 12:25

1

See this example, you want to add to the list conditionally. Without the word "return", all ifs will be executed and add to the ArrayList!

    Arraylist<String> list =  new ArrayList<>();

    public void addingToTheList() {

    if(isSunday()) {
        list.add("Pray today")
        return;
    }

    if(isMonday()) {
        list.add("Work today"
        return;
    }

    if(isTuesday()) {
        list.add("Tr today")
        return;
    }
}

edited Oct 20 '16 at 12:25

GreyGoose

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answered Nov 26 '15 at 03:53

iali87

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The ArrayList should have been initialized as: ArrayList list = new ArrayList<>(); – The_Martian Jan 12 '16 at 08:26

What does the return keyword do in a void method in Java?

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