public  class  Swap2 {       
   public  static  void  Swap2 (IDemo a, IDemo b) {       
       int temp = a.i;       
       a.i = b.i;       
       b.i = temp;       
   }
      
   public   static   void  main (String args []) {       
       IDemo a, b;       
       a =  new  IDemo ( 10 );       
       b =  new  IDemo ( 20 );  
       System.out.println ( "a is "  + a);       
       System.out.println ( "b is "  + b); 
       Swap2.Swap2 (a, b);       
       System.out.println ( "a is "  + a);       
       System.out.println ( "b is "  + b);       
   }

}

class IDemo
{
    protected int i;
    public IDemo(int _i)
    {
        i=_i;
    }

    public String toString()
    {
        return String.valueOf(i);
    }
}

---------- java ----------
a is 10
b is 20
a is 20
b is 10

Output completed (1 sec consumed) - Normal Termination