A good answer might be:

The class of the object.

Card Polymorphism

It makes sense that the object's method is invoked, since, after all, the object's data is used by the method. Here is an example from the previous chapter: 

 . . . .                           // class definitions as before

public class CardTester
{
  public static void main ( String[] args ) throws IOException
  {

    Card card = new Holiday( "Amy" );
    card.greeting();                      //Invoke a Holiday greeting()

    card = new Valentine( "Bob", 3 );
    card.greeting();                      //Invoke a Valentine greeting()

    card = new Birthday( "Cindy", 17 );
    card.greeting();                      //Invoke a Birthday greeting()

  }
}

The reference variable card is used three times, each time with a different class of object. Since Card is a parent to the three different classes, the variable card can be used for each.

QUESTION 6:

Could a variable Valentine val be used with a Holiday object?

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