21. Equivalence of Aliases



Answer:
Yes. You have to be careful how you use the result, however.







alias-detector



    










aliasEg






Here is the example program (again!) with this modification:




    
        

        

        

            
                
import java.awt.*;
class EqualsDemo4
{
  public static void main ( String arg[] )
  {
    Point pointA = new Point( 7, 99 );     // pointA refers to a Point Object
    Point pointB = pointA;                 // pointB refers to the same Object 

    if ( pointA.equals( pointB ) )
    {
      System.out.println( "The two variables refer to the same object," );
      System.out.println( "or different objects with equivalent data." );
    }
    else
      System.out.println( "The two variables refer to different objects" );     

  }
}

            		
        

    


The picture of the situation is the same as before. But now the equals() method is used. It:
  1. Uses the reference pointA to get the x and y from the object.
  2. Uses the reference pointB to get the x and y from the same object.
  3. Determines that the two x's are the same and that the two y's are the same.
  4. Returns a true.
The fact that the object is the same object in step 1 and step 2 does not matter. The x's that are tested are the same, and the y's that are tested are the same, so the result is true.





Question 21:
If the == operator returns a true will the equals() method return a true, always?