Design pattern (computer science)

They allow one to make use of the knowledge of past designers. Many design projects are confronted with similar problems that demand similar solutions. A design pattern is an abstraction of the best solutions for a particular class of problems. MVC or model view controller triad is a classical example of design pattern. It was introduced 1980 in the Smalltalk system.

The book that introduced the term design pattern to software development, Design Patterns: elements of reusable object-oriented software (commonly shortened to GoF) says:

[Design patterns] solve specific design problems and make object-oriented designs more flexible and elegant, and ultimately reusable. They help designers reuse successful designs by basing new designs on prior experience. A designer who is familiar with such patterns can apply them immediately to design problems without having to rediscover them.

In computer programming, the incredible gap in productivity between amateurs and experts is partly a difference in experience. Experts have weathered a variety of problems repeatedly. Typically experts end up with the same pattern to solve the problems as each other's. That is a design pattern. (GoF)

Each pattern comes up with the problem that happens again and again among programmers. Then it shows a typical solution for such a problem, if not the best solution, along with the trade-off, which is a convenient assessment to make prior to applying a potentially costly solution. It is important that patterns accompany a name because it makes possible to describe problems, solutions and talk about them with other folks.

For example the classical MVC pattern is actually a combination of three patterns listed below - Observer, Composite and Strategy. It is broadly used today.

Frequent problems that occur in programming are sometimes less commonly called anti-pattern.

See also amelioration pattern[?]

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

Life cycle patterns

• Compatible suite upgrade pattern
• Incompatible suite upgrade pattern

Social / other

• Community life cycle
• Democracy pattern[?]
• Melting pot
• Constraint system

Related Topics

• Pattern Mining
• Programming practice

Reference and External Links

• Java J2EE pattern catalog (http://java.sun.com/blueprints/corej2eepatterns/Patterns/index)
• 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 (http://www.mindspring.com/~mgrand/pattern_synopses.htm)