Visual Basic 2005 for Programmers: Deitel Developer Series, Second Edition

11.2. Polymorphic Video Game

Suppose we design a video game that manipulates objects of many different types, including objects of classes Martian, Venutian, Plutonian, SpaceShip and LaserBeam. Imagine that each class inherits from the common base class called SpaceObject, which contains method draw. Each derived class implements this method in a manner appropriate to that class. A screen-manager program maintains a collection (e.g., a SpaceObject array) of references to objects of the various classes. To refresh the screen, the screen manager periodically sends each object the same message—namely, draw. However, each object responds in a unique way. For example, a Martian object might draw itself in red with the appropriate number of antennae. ...