creation: 2/14/99; revisions: 2/25/99, 7/17/99, 01/24/00, 07/28/2002, 06/05/03
Classes in a hierarchy are related by the "is-a" relationship. For example, a Nissan is-a Automobile, and a Sentra is-a Nissan. This chapter discusses how reference variables are used for objects from different classes within a hierarchy. Another subject is the idea of an abstract class — a class that cannot be instantiated but that can be the parent of other classes.