Java™ How To Program (Early Objects), Tenth Edition

Quadrilaterals

If class Rectangle is derived from class Quadrilateral, then a Rectangle object is a more specific version of a Quadrilateral. Any operation (e.g., calculating the perimeter or the area) that can be performed on a Quadrilateral can also be performed on a Rectangle. These operations can also be performed on other Quadrilaterals, such as Squares, Parallelograms and Trapezoids. The polymorphism occurs when a program invokes a method through a superclass Quadrilateral variable—at execution time, the correct subclass version of the method is called, based on the type of the reference stored in the superclass variable. You’ll see a simple code example that illustrates this process in Section 10.3.