[jdjlist] Re: Java : pass by reference???

[Madhav Vodnala]

Hi Shankar

 

Here is my take on 'pass by reference' theory.

 

Here are the absolute statements about 'pass by reference'

 

    1)  Pass by reference works for all Classes, except Strings and arrays.

    2 ) Primitive data types are always passed by  'value'.

I think this is very straight forward and can be verified with any small example.

 

Now lets analyze your code.

Check out the following code. I just replaced the method call with its equivalent

code. I mean the code is exactly the same as 'calling' the method.

 

 

public static void main (String[] args)

{

    test objTest = new test();
    String testfill = new String("main");
//    objTest.fill(testfill);

               

    String objTest_fill_fillMe = testfill;

    objTest_fill_fillMe = "test"; // same as objTest_fill_fillMe = new String ("text");

    System.out.println("Fill me result:" + testfill);
    Integer intFill = new Integer(200);
//    objTest.fill(intFill);

    Integer objText_fill_fillMe = intFill;

    objTest_fill_fillMe = new Integer (100);

    System.out.println("Fill me result:" + intFill);

}

 

Now, in first case, String variable testfill is not passed by reference.

 

secondly, local variable 'fillMe' first refers to the value that is being passed and

refers the new object created with new. so its nothing but changing the local variable value.

 

SO, the theory is

 

If you assign the new object (created with new ) to the function argument (which refers to the calling method variable) and modify its

content, it doesnt modify the calling method's variable value, irrespective of whether calling method's variable is passed by value or passed by

reference.

 

 

-Madhav

 

----- Original Message -----

From: "H Shankaranarayanan" <[EMAIL PROTECTED]>

To: "JDJList" <[EMAIL PROTECTED]>

Sent: Friday, May 31, 2002 1:00 PM

Subject: [jdjlist] Java : pass by reference???

> class test
> {
>     /**
>      *  Description of the Method
>      *
>      *@param  fillMe  Description of the Parameter
>      */
>     public void fill(String fillMe)
>     {
>         fillMe = "test";
>     }
>
>
>     /**
>      *  Description of the Method
>      *
>      *@param  fillMe  Description of the Parameter
>      */
>     public void fill(Integer fillMe)
>     {
>         fillMe = new Integer(100);
>     }
>
>
>     /**
>      *  Description of the Method
>      *
>      *@param  args  Description of the Parameter
>      */
>     public static void main(String args[])
>     {
>
>         try
>         {
>             test objTest = new test();
>             String testfill = new String("main");
>             objTest.fill(testfill);
>             System.out.println("Fill me result:" + testfill);
>
>             Integer intFill = new Integer(200);
>             objTest.fill(intFill);
>             System.out.println("Fill me result:" + intFill);
>
>         } catch (Exception e)
>         {
>             e.printStackTrace();
>         }
>     }
> }
>
>
> That is a sample program i wrote to test this fact. The result is dependent
> on scope of the variable.
> So wots this pass by reference concept that every text book around the world
> states about Java.
>
> How does the pass by reference concept work anyways?
>
> I might have missed something here. If i did i would appreciate if anyone
> told me wot is it that i did miss.
>
> I was expecting this program to work otherwise but it does not.
>
> --Shankar
>
>
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