FactoryMethod

Origin:

GoF 95

Reason:

Provide an interface for creating an object, but let subclasses decide which class to instantiate (aka virtual constructor).

Synopsis:

An abstract class, the FactoryMethod, defines abstract or near-empty methods that return product components and a final creator method to create an entire product. Subclasses override methods that return product components but use the same creator.

Example:

An office productivity program manages two classes: Document, e.g., texts, images, sounds, etc., and Application to create or open documents. The Application class does not know which specific Document class to instantiate.

Solution:

Product	Interface of objects the factory method creates.	Abstract document
ConcreteProduct	Implements Product for a specific document.	Text or image or sound, etc., document.
Creation Requestor	Application-independent class that creates (indirectly via a factory class) application-specific objects.
Factory IF	Declares the factory method that returns a Product.
Factory Class	Application-specific class with method to create Concrete Products. Implements Factory IF.	DocumentFactory, ImageFactory