With the foregoing description of objects, inheritance, and interfaces in hand, we are now ready to begin discussing design patterns in earnest. Recall that these are merely recipes for writing better object-oriented programs. We have divided them into the Gang of Four's three groups: creational, structural, and behavioral. We'll start out in this section with the creational patterns.

All of the creational patterns deal with ways to create instances of objects. This is important because your program should not depend on how objects are created and arranged. In VB6, of course, the simplest way to create an instance of an object is by using the new operator.

set fred1 = new Fred              'instance of Fred class

However, this really amounts to hard coding, depending on how you create the object within your program. In many cases, the exact nature of the object that is created could vary with the needs of the program, and abstracting the creation process into a special “creator” class can make your program more flexible and general.

The Factory Method pattern provides a simple decision-making class that returns one of several possible subclasses of an abstract base class, depending on the data that are provided. We'll start with the Simple Factory pattern as an introduction to factories and then introduce the Factory Method pattern as well.

The Abstract Factory pattern provides an interface to create and return one of several families of related objects.

The Builder pattern separates the construction of a complex object from its representation so that several different representations can be created, depending on the needs of the program.

The Prototype pattern starts with an instantiated class and copies or clones it to make new instances. These instances can then be further tailored using their public methods.

The Singleton pattern is a class of which there can be no more than one instance. It provides a single global point of access to that instance.