C# 3.0 Design Patterns

Pattern Comparison

The Builder and Abstract Factory patterns are similar in that they both look at construction at an abstract level. However, the Builder pattern is concerned with how a single object is made up by the different factories, whereas the Abstract Factory pattern is concerned with what products are made. The Builder pattern abstracts the algorithm for construction by including the concept of a director. The director is responsible for itemizing the steps and calls on builders to fulfill them. Directors do not have to conform to an interface.

A further elaboration on the theme of creating products is that instead of the client explicitly declaring fields of type ProductA and ProductB, say, the Product object the builder returns is actually a list of parts, which can have different lengths and contents depending on the director that was in charge at its creation.

A comparison of the two patterns is given in Table 6-1.

Table 6-1. Comparison of Abstract Factory and Builder patterns

Criteria	Abstract Factory	Builder
Client aggregates	A Factory and Products	A Director, Builders, and a Product
Product creation is via	A factory	A director
Product creation invokes	CreateProductA	Construct(builder)
Factory/Builder returns	A specific product	A part of a product
Product has	Specific properties	A list of parts