design pattern: builder v.s. factory

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原文见: http://stackoverflow.com/questions/757743/what-is-the-difference-between-builder-design-pattern-and-factory-design-pattern

The Factory pattern can almost be seen as a simplified version of the Builder pattern.

In the Factory pattern, the factory is in charge of creating various subtypes of an object depending on the needs.

The user of a factory method doesn't need to know the exact subtype of that object. An example of a factory method createCar might return a Ford or a Honda typed object.

In the Builder pattern, different subtypes are also created by a builder method, but the composition of the objects might differ within the same subclass.

To continue the car example you might have a createCar builder method which creates a Honda-typed object with a 4 cylinder engine, or a Honda-typed object with 6 cylinders. The builder pattern allows for this finer granularity.

Diagrams of both the Builder pattern and the Factory method pattern on available on Wikipedia.

With design patterns, there usually is no "more advantageous" solution that works for all cases. It depends on what you need to implement.

From Wikipedia:

Builder focuses on constructing a complex object step by step. Abstract Factory emphasizes a family of product objects (either simple or complex). Builder returns the product as a final step, but as far as the Abstract Factory is concerned, the product gets returned immediately.
Builder often builds a Composite.
Often, designs start out using Factory Method (less complicated, more customizable, subclasses proliferate) and evolve toward Abstract Factory, Prototype, or Builder (more flexible, more complex) as the designer discovers where more flexibility is needed.
Sometimes creational patterns are complementary: Builder can use one of the other patterns to implement which components get built. Abstract Factory, Builder, and Prototype can use Singleton in their implementations.

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