Java™ How to Program, Seventh Edition

9.2. Superclasses and Subclasses

Often, an object of one class is an object of another class as well. For example, in geometry, a rectangle is a quadrilateral (as are squares, parallelograms and trapezoids). Thus, in Java, class Rectangle can be said to inherit from class Quadrilateral. In this context, class Quadrilateral is a superclass and class Rectangle is a subclass. A rectangle is a specific type of quadrilateral, but it is incorrect to claim that every quadrilateral is a rectangle—the quadrilateral could be a parallelogram or some other shape. Figure 9.1 lists several simple examples of superclasses and subclasses—note that superclasses tend to be “more general” and subclasses “more specific.”

Figure 9.1. Inheritance examples.

Superclass ...