Dear Henry, Happy 12th Birthday Dear Henry, Happy 12th Birthday How you have grown!! Love, Alice
The top class in a hierarchy is called the root of the hierarchy.
The root of the hierarchy of cards is the class Card.
A variable of the root type, Card, can be used with any
of its descendants.
When a program uses several related objects, it is often useful to have a reference variable than can be used with any of them.
Card crd = new YouthBirthday( "Valerie", 7 ); crd.greeting(); // print a youth birthday greeting crd = new AdultBirthday( "Walter", 47 ); crd.greeting(); // print an adult birthday greeting crd = new Birthday( "Zoe", 30 ); crd.greeting(); // print a generic birthday greeting crd = new Holiday( "Kelly" ); crd.greeting(); // print a holiday greeting crd = new Valentine( "Jill", 42 ); crd.greeting(); // print a valentine greeting
(Thought Question: ) Say that you had a collection of 12 greeting card objects and wanted to keep them in an array. What type of array should you use?