How to increment an integer by reference?

Question

Is it possible to increment an integer value by reference?

int counterA = 0;
int counterB = 0;

int counter = (condition) ? counterA : counterB;
//use counter
counter++;

Result: both counterA + counterB will remain = 0, instead being incremented.

That's great, would you mind adding this as an answer. Probably what I was looking for. — membersound, Nov 04 '14 at 16:18
@Makoto You're correct. I'm going to drink more coffee now and cry over my having said that. — Zéychin, Nov 04 '14 at 16:23

score 4 · Accepted Answer · answered Nov 04 '14 at 16:18

4

int is a primitive type so there is no reference being assigned, only values. You can wrap it in a class:

public class IntegerHolder {
   private int value;

   public IntegerHolder(int value) {
       this.value = value;
   }

   public void increment() {
       value++;
   }
   ...
}

answered Nov 04 '14 at 16:18

M A

71,713
13
134
174

OK I accept this as a valid answer, though one would probably perfer the use of `AtomicInteger` directly. – membersound Nov 04 '14 at 16:20
You could just use the Integer class. – Zéychin Nov 04 '14 at 16:21
4

@Zéychin no, it's immutable. – assylias Nov 04 '14 at 16:22
`Integer x = 0; x++;` is completely valid, as are the arithmetic operations. – Zéychin Nov 04 '14 at 16:27
It's still creating a new instance of an integer under the covers. Don't let the syntactic sugar fool you. – Makoto Nov 04 '14 at 16:31

score 4 · Answer 2 · answered Nov 04 '14 at 16:20

4

As an alternative to an int holder you can also use an array:

int[] counter = new int[1];

counter[0]++;

answered Nov 04 '14 at 16:20

assylias

321,522
82
660
783

score 1 · Answer 3 · edited May 23 '17 at 10:33

Short answer : use AtomicInteger :

AtomicInteger counterA = new AtomicInteger();
AtomicInteger counterA = new AtomicInteger();

AtomicInteger counter = (condition) ? counterA : counterB;
counter.incrementAndGet();

In Java, all variables are pass-by-value, including primitive types like integer (and even objects but it may be confusing here, just check there).

You could be tempted to use Integer but wrapper classes are immutable. Instead you can use AtomicInteger which is mutable.

score 0 · Answer 4 · answered Nov 04 '14 at 16:27

As an alternative to a wrapper object (the answer you've been provided by other users) you could just use an if-else statement and increment the values directly:

int counterA = 0;
int counterB = 0; 

if(condition)
{
    counterA++;
}
else
{
    counterB++;
}

This can become too wieldy if you have more than 2 counters though.

How to increment an integer by reference?

4 Answers4