/*
  An example from Java: A beginners's guide by Herbert Schildt that
  illustrates the the strongly typed nature of Java.  A reference for one
  type of object cannot normally refer to another type of object except
  whne a reference of a superclass is referred to an object that's a
  subclass.
  v1 - won't compile.
  v2 - uses inheritance and will compile
*/
public class Driverv1
{
    public static void main (String [] args)
    {
	Xv1 x = new Xv1(10);
	Xv1 x2;
	Yv1 y = new Yv1(5);
	x2 = x;     // OK, both of the same type
	x2 = y;   // Not OK, not of the same type
    }
}