Java adding to an integer using methods

Question

I am having trouble with a relatively simple problem: I am trying to use a method from another class to add to an integer in my main class but the value of my integer is not increasing, the value stays the same, this is what the code looks like:

public class prog{

/**
 * @param args
 * @throws MidiUnavailableException 
 */

public static void main(String[] args) {
int num = 11;
thing.add(num);
System.out.println(num);
}
}

and the class 'thing' being:

public class chords2 {

static void add(int val){
    val = val+9;

}

}

any tips on how to get this to work is most appreciated

possible duplicate of [How do I pass a primitive data type by reference?](http://stackoverflow.com/questions/4319537/how-do-i-pass-a-primitive-data-type-by-reference) — Raedwald, May 01 '14 at 13:00

score 1 · Accepted Answer · answered Apr 08 '14 at 04:33

1

In Java, int is passed by value. If you want to add you should return the value and reassign it.

static int add(int val){
    return val+9;
}

Then, to call it,

int num = 11;
num = thing.add(num);

answered Apr 08 '14 at 04:33

merlin2011

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2

Not just `int`, everything is pass by value. – Keppil Apr 08 '14 at 04:36
1

@Keppil, True, but most objects are references, and I did not want to go into an extended discussion about reference vs value types. So I made a true statement which is slightly incomplete. – merlin2011 Apr 08 '14 at 04:38
Fair enough, I suppose. – Keppil Apr 08 '14 at 04:44
Thanks I just needed to re-assign the value this one worked perfectly – Apr 08 '14 at 05:26

score 1 · Answer 2 · edited May 23 '17 at 12:21

1

What happens is that Java is always pass-by-value. So, in your example, if you modify the integer val inside the method, it won't have effect outside.

What can you do?

You can declare your method to return an integer, then you assign the result to the variable you want:

static int add(int val){
    return val + 9;    
}

and when you call it:

int num = 11;
num = SomeClass.add(num); // assign the result to 'num'

edited May 23 '17 at 12:21

Community

1
1

answered Apr 08 '14 at 04:40

Christian Tapia

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@AmirBawab why are you saying that? – Christian Tapia Apr 08 '14 at 04:42
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Yes @Amir, everything in Java is pass by value. – Keppil Apr 08 '14 at 04:48
@AmirBawab I will recommend you to read [this](http://stackoverflow.com/questions/40480/is-java-pass-by-reference). – Christian Tapia Apr 08 '14 at 04:50
Yes, it's confusing. Despite that, my answer is correct, so if you downvoted, please undo it. **Also**, you say *"value mean, copy of the data inside the variable..."*, but note that an object's value is a *reference*. – Christian Tapia Apr 08 '14 at 04:59

score 0 · Answer 3 · answered Apr 08 '14 at 04:33

0

You should have a private int val in your thing class, otherwise add "return" statement to your add() method and set the return value back in calling position.

answered Apr 08 '14 at 04:33

D.S

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Java adding to an integer using methods

3 Answers3