Design pattern (computer science)

Design patterns are recurring solutions to problems in object-oriented design. The phrase was introduced to computer science in the 1990s by the text Design Patterns: elements of reusable object-oriented software. The scope of the term remained a matter of dispute into the next decade. Algorithms are not thought of as design patterns, since they solve implementation problems rather than design ones. Typically, a design pattern is thought to encompass a tight interaction of a few classes and objects.

Interest in sharing patterns in the software community has led to a number of books, symposiums, and the formation of Ward Cunningham's original wiki. The goal of pattern literature is to make the experience of past designers accessible to beginners and others in the field. A book of design patterns presents different solutions in a common format, to provide a language for discussing design issues.

Table of contents

1 Pattern Format 1.1 Name 1.2 Problem 1.3 Solution 1.4 Consequences 2 Similar Terms 3 A List of Design Patterns 3.5 Fundamental patterns 3.6 Creational patterns 3.7 Structural patterns 3.8 Behavioral patterns 3.9 Concurrency patterns 3.10 RealTime patterns 4 Related Topics 5 References 6 External links

Pattern Format

The design pattern format has four essential parts, although names and ordering differ by source:

Name

Every pattern needs a name, to provide a language for design discussion.

Problem

Recurring circumstances lead to the discovery of this pattern by multiple persons. A primary goal of design is to limit the amount of source change needed to change a program's observed behavior, but this can be difficult to achieve if a designer does not understand the implications of a design.

Solution

The solution is described sufficiently for implementation by novices, although the implementation is usually given in general enough terms that it can be adapted to different projects.

Consequences

Applying this solution will effect the rest of the project in certain ways, so it is important to mention any common negative or serendipitous side-effects.

Similar Terms

Poor (yet unfortunately common) solutions to common problems are sometimes known as anti-patterns.

See also amelioration pattern

A List of Design Patterns

Fundamental patterns

• Delegation pattern
• Interface pattern
• Proxy pattern
• Immutable pattern
• Marker Interface pattern

Creational patterns

• Abstract factory pattern
• Anonymous subroutine objects pattern
• Builder pattern
• Factory method pattern
• Prototype pattern
• Singleton pattern - an object which is unique in its kind in the whole system

Structural patterns

• Adapter pattern
• Bridge pattern
• Composite pattern - a pattern to build large structures
• Container pattern
• Decorator pattern
• Extensibility pattern
• Facade pattern
• Flyweight pattern
• Pipes and filters
• Proxy pattern

Behavioral patterns

• Breadth first recursion
• Chain of responsibility pattern
• Command pattern
• Currying concept
• Event listener
• Interpreter pattern
• Iterator pattern
• Mediator pattern
• Memento pattern
• Observer pattern - one object acts when some value of another objects changes
• State pattern
• Strategy pattern - make an algorithm pluggable
• Template method pattern
• Visitor pattern
• Hierarchical visitor pattern

Concurrency patterns

• Action at a distance pattern
• Balking pattern
• Guarded suspension
• Scheduler pattern
• Read write lock pattern
• Double checked locking pattern
• Disable job requests while running job pattern

RealTime patterns

• Scheduled task pattern
• User interface pattern
• Disable job requests while running job pattern

Related Topics

• Pattern Mining
• Programming practice
• Refactoring

References

• Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides: Design Patterns, Addison-Wesley, 1995, hardcover, 395 pages, ISBN 0201633612, Design Patterns CD, 1997 ISBN 0201634988
• Frank Buschmann, Regine Meunier, Hans Rohnert, Peter Sommerlad, Michael Stal: Pattern-oriented Software Architecture, Volume 1: A System of Patterns, John Wiley & Sons Ltd., ISBN 0471958697
• Douglas Schmidt: Pattern-oriented Software Architecture. Volume 2: Patterns for Concurrent and Networked Objects, John Wiley & Sons Ltd., ISBN 0471606952
• Alan Shalloway, James R. Trott: Design Patterns Explained: A New Perspective on Object-Oriented Design, Addison-Wesley, ISBN 0201715945
• Martin Fowler: Patterns of Enterprise Application Architecture, Addison-Wesley, ISBN 0321127420

External links

• Java J2EE pattern catalog
• One of many Perl design patterns wiki sites
• The list of design patterns is entirely based on a wiki page http://c2.com/cgi/wiki?CategoryPattern.
• The definition of design pattern is based on the definition in Design Patterns.
• Many design patterns are described in mgrand's book
• Patterns Catalog
• The Object-Oriented PatternDigest
• Design Pattern Toolkit