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

10.2. Base Classes and Derived Classes

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 Visual Basic, class Rectangle can be said to inherit from class Quadrilateral. In this context, class Quadrilateral is a base class and class Rectangle is a derived class. 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 10.1 lists several simple examples of base classes and derived classes—note that base classes tend to be “more general” and derived classes tend to be “more specific.” ...