Pass By reference Doubt

[Muneeswaran Balasubramanian]

Hi to all,

I am stuck with Pass by reference,Here is the my code

class Sample
{

    String name;

    public Sample()
    {
        name = "Ram";
    }
}

class TestPassByReference
{

    public static void main(String[] args)
    {
        Sample s1 = new Sample();
        System.out.println("Before change value");
        System.out.println("S1 : " + s1);
        System.out.println("Date : " + s1.name);

        changeValue(s1);

        System.out.println("After change value");
        System.out.println("S1 : " + s1);
        System.out.println("Date : " + s1.name);

    }

    public static void changeValue(Sample s)
    {
        s.name = "Raju";
        s = null;
        return;
    }
}

Output:

Before change value
S1 : com.inofo.scjp.Sample@f62373
Date : Ram
After change value
S1 : com.inofo.scjp.Sample@f62373
Date : Raju

In this code,by the context of pass by reference we have change the name from Ram to raju.Its takes the effect.But after that i have assign null to the reference,thats not makes effect.
that means that doen't make object as null.Why?

Please clarify my doubt.

[Mohamed Sanaulla]

The s referred to in the changeValue method is made to point to a null location and not the s1 referred to in the main. When the changeValue method begins to execute- both s and s1 would be referring to the same object (that explains the reason why the name changed), but when you try to reference s to a null, only s points to a null and not the s1. s1 still continues to refer to the valid object on the heap.

[Matthew Brown]

There is no pass-by-reference in Java. It passes references by value.

See CallByReferenceVsCallByValue for more detail.

[Mohamed Sanaulla]

Matthew Brown wrote:There is no pass-by-reference in Java. It passes references by value.

See CallByReferenceVsCallByValue for more detail.

Oh yeah, how did I miss this point!

[Muneeswaran Balasubramanian]

Hi Both of you ,

Thanks for your reply.It makes me clear.

[Ikpefua Jacob-Obinyan]

Hello Guys,
At first this statement 'pass-by-reference' gave me serious headache till I spent a whole day writing codes to understand what was going on. If I my voice could be heard I would have suggested that the statement should be changed from 'pass-by-reference' to 'pass-by-reference-values'.

However...@Mohamed take note that if you write this same program to change a primitive type, -unlike objects- the value does NOT change

Something 'similar' could pop up in the real exams

Take NOTE of the following modification to your program:

class Sample  
{  
  
  int i;  
  public Sample() {
	i = 10;
}    
}  
class TestPassByReference  
{  
  
    public static void main(String[] args)  
    {  
        Sample s1 = new Sample();
        System.out.println("Before change value");  
        System.out.println("S1 : " + s1); 
        System.out.println("Date : " + s1.i);
       
  
        changeValue(s1.i);  
  
        System.out.println("After change value");
        System.out.println("S1 : " + s1); 
        System.out.println("Date : " + s1.i);  
  
    }  
  
    public static void changeValue(int j)  
    {  
       j = 30; 

       j = 0;
       
        return;  
    }  
}  

Output:

Before change value
S1 : com.inofo.scjp.Sample@f62373 
Date : 10
After change value
S1 : com.inofo.scjp.Sample@f62373
Date : 10

[Ikpefua Jacob-Obinyan]

Hey Munees!...Its good to see you here ...once again we are putting into "PRACTICE" our thoughts.

[Mohamed Sanaulla]

Ikpefua Jacob-Obinyan wrote:
However...@Mohamed take note that if you write this same program to change a primitive type, -unlike objects- the value does NOT change

That's why it is called pass by values. And the values are copied- in case of references- the location of the instance (that is the value the references hold) and in case of primitives the value of the primitive.