Java Illuminated, 5th Edition

10.5 Abstract Classes and Methods

In our Bank Account hierarchy, we could instantiate BankAccount objects, CheckingAccount objects, and SavingsAccount objects. In some situations, however, we will design a class hierarchy where one or more classes at the top of the hierarchy are not intended to be instantiated. Rather, they typically specify patterns for methods that subclasses in the hierarchy must implement. Often, the superclasses do not implement these methods. In these situations, we do not intend that these superclasses will be used to instantiate objects, and we define the superclasses as abstract.

An abstract class is a class that is intended to be extended, rather than instantiated. Usually, an abstract class contains at least one ...