There are 4 classes. Why can only 3 be instantiated?

A good answer might be:

The parent class Card is an abstract class and therefore cannot be instantiated.

The program can't do the following:

. . . . public static void main ( String[] args ) throws IOException { . . . . Card card = new Card() ; // can't instantiate abstract class card.greeting() ; . . . . }

Because Card is an abstract class, the compiler would say this is a syntax error. However, the following is OK:

. . . . public static void main ( String[] args ) throws IOException { . . . . Card card = new Valentine( "Joe", 14 ) ; // a Valentine is-a Card card.greeting() ; . . . . }

It is OK to save a reference to a Valentine object in a reference variable of type Card because Valentine is-a Card. You can think of the reference variable card as being a card rack designed to hold any specific instance of a Card.

QUESTION 11:

Do you think it would be OK to do the following?

• Card card2 = new Holiday( "Bob" ) ;
• Card card3 = new Birthday( "Emily" ) ;