Doubt in Parameter Passing

[Suresh Rajadurai]

Hi Folks,

Please note the following program:

class TestBuffer
    {
      public void myBuf( StringBuffer s1, StringBuffer s2)
        {
             System.out.println("S1 Before Append :" + s1);
             s1.append(" how are you") ;
             System.out.println("S1 After Append  :" + s1);
             s1 = s2;
             System.out.println("S1 after s1=s2   :" + s1);
        }

     public static void main ( String args[] )
        {
              TestBuffer tb = new TestBuffer();
              StringBuffer s1 = new StringBuffer("Hello");
              StringBuffer s2 = new StringBuffer("Doing");
              tb.myBuf(s1, s2);
              System.out.println("Final Output in Main Method  :" + s1);
       }
   }

It is giving the following output:

S1 Before Append : Hello
S1 After Append : Hello How are you
S1 After S1=S2 : Doing
Final Output in Main Method : Hello How Are you.

Could you please explain me why it is NOT printing "Doing" in the last output (it has been changed to "doing" in the method myBuf() ?
In the statement "s1=s2", if s1 and s2 are local to the method myBuf(),
then why in the statement s1.append("how are you") , s1 is not local to the method myBuff().

I am a bit confused. A good explanation is GREATLY APPRECIATED.

Thanks in advance

Best Regards

Suresh

[James Tharakan]

s1=s2; in the method is modifing the reference of s1 which is created in the method and that s1 is not same as the reference in the main method

[Campbell Ritchie]

We have an FAQ which may help.