x = 3; y = 5
x = 45; y = 83

Mutable MyPoint

As the example program shows, a MyPoint object can be changed by any method that has a reference to it.

Note: If a reference to a MyPoint object is passed as a parameter, then the invoked method can use that reference to change the public instance variables of the object.

Here is the example program with another class:

class MyPoint
{
  public int x=3, y=5 ;

  public void print()
  {
    System.out.println("x = " + x + 
        "; y = " + y );
  }
}

class PointDoubler
{
  public void twice( MyPoint parm )
  {
    System.out.println("Enter PointDoubler");
    parm.print() ;
    parm.x = parm.x * 2 ;
    parm.y = parm.y * 2 ;
    parm.print() ;
    System.out.println("Leave PointDoubler");
  }
}

class PointTester
{
  public static void main ( String[] args )
  {
    MyPoint pt = new MyPoint();

    PointDoubler dbl = new PointDoubler();

    pt.print();

    dbl.twice( pt );

    pt.print();
  }
}

x =   y = 


Enter PointDoubler
x =   y = 


x =   y = 


Leave PointDoubler


x =   y =