passing param

[Tanuja Vaid]

lass ValHold{
public int i = 30;
}
public class ObParm{
public static void main(String argv[]){
ObParm o = new ObParm();
o.amethod();
}
public void amethod(){
int i = 99;
ValHold v = new ValHold();
v.i=30;
another(v,i);
System.out.println(v.i);//2
}//End of amethod
public void another(ValHold v, int i){
i=0;
v.i=20;
ValHold vh=new ValHold();
v=vh;
System.out.println(v.i+ " "+i);//3
}//End of another
}
can someboyd give me a detailed explanation of why v.i on line 3 prints 30,while v.i on line 2 prints 20

[Corey McGlone]

Tanuja,
The reason you're seeing the difference is because of the lines:

ValHold vh=new ValHold();
v=vh;

When these lines are executed in the method another(), the value of the formal parameter v is changed to reference a new object. You now have two distinct ValHold objects. You have the initial one, which you modified to hold a value of 20 and the new one, which is initialized to hold a value of 30.
That's why you see the two different values - you have two different objects.
Corey

[Valentin Crettaz]

Tanuja,
Here is an exceptionnal second warning about your name!
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[swapna sivaraju]

hi Tanuja
In java when we pass an object reference as a paramter in a method call..the copy of the reference value is actually passed rather than the reference itself..
so in the call another(v.i,i)...we are passing a copy of the reference value(ie. the address stored in the v). to the method.So the actual parameter
(Valhold v) in the method void another(ValHold v, int i) is the copy of the reference value in the formal parmeter in the method call.
so,
in the call another(v.i,i)--v.i=30
in the method
--- we are changing the value at the same location by the statement v.i=20;
so now the actual value has been changed.
but then we are creating another object of valhold v which is not same as the previous one..
ie. ValHold v = new ValHold();
and now v.i=30;
makes another object with it's i= 30.

hence , line 2 prints 20 and 3 prints 30.
I hope this is confusing.
swapna

[Corey McGlone]

If you're still confused about how parameters are passed in Java, you might want to check this out. I made it just to clear up this issue.
HTH,
Corey