JQ+ Qs.....

[Arun Mishra]

Hi all,

 
import java.util .*;
public class TestClass
{
   public static void main(String args[])
   {
      Stack s1 = new Stack ();
      Stack s2 = new Stack ();
      processStacks (s1,s2);
      System.out.println (s1 + "    "+ s2);
   }
   public static void processStacks(Stack x1, Stack x2)
   {
      x1.push (new Integer ("100"));
      x2 = x1;
   }
 }

Could someone please explain, why the answer is [100][] ? I think it should be[100][100] as the parameters for the methods are Object.
Thanks,
Arun

[Valentin Crettaz]

Even objects are passed by value. In this case, the reference (not the whole stack object) s1 and s2 are copied and passed to the method processStacks. Inside the method, if you change the reference (x2=x1) then the change is not reported outside the method because the reference were copied... That is, outside the method, s1 and s2 will still refer to their initial stack.
(Imagine the nightmare it would be to find a bug if reference passing was allowed in Java. I find it much more better that way, but it's a matter of personal taste, of course.)
HIH

[Arun Mishra]

Thanks Valentin,
Could you please explain me how we can differentiate whether the parameter is whole object or reference ?
Arun

[Valentin Crettaz]

"whole" objects are never passed as parameters only (a copy of) the reference to the object is passed.
There is an interesting document about that: Javaranch: pass-by-Value Please
HIH
[ January 22, 2002: Message edited by: Valentin Crettaz ]

[Arun Mishra]

Thanks Valentin

[mark stone]

need some qustions or code to practice this. can you send me some links or resources ?

Originally posted by Valentin Crettaz:
"whole" objects are never passed as parameters only (a copy of) the reference to the object is passed.
There is an interesting document about that: Javaranch :-P ass-by-Value Please
HIH