public class Demo
{
   public static void main( String[] args )
   {
      ClassB  b = new ClassB();

      ClassA  a;

      a = b;    // Upcasting (with automatic conversion)


      /* =================================
         Undoing the upcasting operation:
         ================================= */

      ClassB b2;

      b2 = (ClassB) a;         // Downcasting that undo the 
                               // previous upcasting operation
   }
}