SE450: Creational Patterns: Factory Method [11/12]

• Name - Factory Method
• A.K.A. - Virtual Constructor
• Intent - Define an interface for creating an object, but let subclasses decide which class to instantiate. Defers intantiation to subclasses.
• Problem -
  • A class needs to instantiate a derivation of another class, but doesn't know which one.
  • A class wants its subclasses to specify the objects it creates
• Solution - A derived class makes the decision on which class to instantiate and how to instatiate it.
• Participants and Collaborators
  • Product
  • ConcreteProduct
  • Creator
  • ConcreteCreator
• Consequences
  • Clients might need to subclass the Creator class just to make a particular ConcreteProduct
  • Factory methods eliminate the need to bind application-specific classes into your code. You only deal with generic Product interfaces, allowing ConcreteProducts to be interchanged easily.
  • Provides hooks for subclasses
  • Connects parallel class heirarchies
• Implementation
  • Two types: abstract Factory method, or a concrete Factory method with default implementation
  • Parameterized factory methods: can create multiple product types from one method
  • Naming conventions are a good idea
• GoF Reference (107)
• Example files are here
• The Factory Method allows the creators to be more than just creators for products, they might create a structure using the products created from their factory methods.