Re: Call By Reference

Thomas Hawtin <>
Sun, 19 Aug 2007 06:32:14 +0100
ravi wrote:

 public static void swap(Integer x,Integer y)

That is (I think, I wouldn't write code like that!)

     public static void swap(Integer x, Integer y) {
         x = Integer.valueOf(x.intValue() ^ y.intValue());
         y = Integer.valueOf(y.intValue() ^ x.intValue());
         x = Integer.valueOf(x.intValue() ^ y.intValue());

Can anybody tell me why this program is not giving correct o/p i.e

Anyway, Java is always call by value, even when those values are
references (this makes code very much more easy to follow). Your code is
just changing the references (which are copies), not the objects pointed to.

You could write something similar that changes the object themselves.
Integer is immutable, so you will need a different type.

import java.util.concurrent.atomic.AtomicInteger;
     public static void swap(
          final AtomicInteger x, final AtomicInteger y
     ) {
         x.set(x.get() ^ y.get());
         y.set(y.get() ^ x.get());
         x.set(x.get() ^ y.get());

Tom Hawtin

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