Visual Basic Design Patterns: VB 6.0 and VB.NET

Chapter 10. The Factory Method

We've just seen a couple of examples of the simplest of factories. The factory concept recurs all throughout object-oriented programming, and we find a few examples embedded in VB itself and in other design patterns (such as the Builder pattern). In these cases a single class acts as a traffic cop and decides which subclass of a single hierarchy will be instantiated.

The Factory Method pattern is a clever but subtle extension of this idea, where no single class makes the decision as to which subclass to instantiate. Instead, the superclass defers the decision to each subclass. This pattern does not actually have a decision point where one subclass is directly selected over another class. Instead, programs written ...