Abstract Factory

Gamma et al. 95

Intent

  • Provide an interface for creating interrelated object families, without specifying their concrete classes.

Motivation

  • Consider, for instance, an application that runs on different graphic systems (e.g. Motif, Presentation Manager)

  • Each graphic element (window, button, etc.) must be created differently, depending on the system used.

  • To do this, an abstract class is used to create the graphic elements

Motivation - example

abstract factory example

Applicability (1/2)

Use an abstract factory when:

  • A system must be independent of how its products are created, composed and represented

  • A system must choose one of several product families

Applicability (2/2)

Use an abstract factory when:

  • The objects of a family must be used together, and we want to reinforce this constraint.

  • We want to propose a library of products, without showing their implementation

Structure

abstract factory structure

Consequences

  • Clients do not know the implementation classes of the families

  • Switching between product groups becomes simple

  • The consistency within a product family is enhanced

  • It is difficult to add new product families.

Implementation Tradeoffs

  • Factories are Singletons

  • Factories define an interface, which can be implemented by a prototype or by a factory method

  • Definition of extensible factories

Author and Date

  • Design Patterns: Elements of Reusable Object-Oriented Software. Erich Gamma, Richard Helm,Ralph Johnson, and John Vlissides. Addison Wesley. October 1994.