Patrones de diseño mediante ejemplos


¿No os ha pasado nunca que encontráis un artículo tan bueno que decís "éste me lo guardo"? ¿Y qué ocurre cuando lo que os ha gustado tanto es un comentario?

No he podido resistirme a hacerme eco de este comentario, encontrado en stackoverflow , de BalusC


You can find an overview of a lot design patterns in Wikipedia . It also mentions which patterns are mentioned by GoF. I'll sum them up here and try to assign as much as possible pattern implementations found in both the Java SE and Java EE API's.


Creational patterns

Builder

Recognizeable by creational methods returning the instance itself

Prototype

Recognizeable by creational methods returning a _different_ instance of itself with the same properties

Singleton

Recognizeable by creational methods returning the same instance (usually of itself) everytime


Structural patterns

Adapter

Recognizeable by creational methods taking an instance of different abstract/interface type and returning an implementation of own/another abstract/interface type which decorates/overrides the given instance

Bridge

Recognizeable by creational methods taking an instance of different abstract/interface type and returning an implementation of own abstract/interface type which delegates/uses the given instance

  • None comes to mind yet. A fictive example would be new LinkedHashMap(LinkedHashSet<K>, List<V>) which returns an unmodifiable linked map which doesn't clone the items, but _uses_ them. The java.util.Collections#newSetFromMap() and singletonXXX() methods however comes close.

Composite

Recognizeable by behavioral methods taking an instance of same abstract/interface type

Decorator

Recognizeable by creational methods taking an instance of same abstract/interface type

Facade

Recognizeable by behavioral methods which internally uses instances of different independent abstract/interface types

Flyweight

Recognizeable by creational methods returning a cached instance, a bit the "multiton" idea

Proxy

Recognizeable by creational methods which returns an implementation of given abstract/interface type which in turn delegates/uses a different implementation of given abstract/interface type

The Wikipedia example is IMHO a bit poor, lazy loading has actually completely nothing to do with the proxy pattern at all


Behavioral patterns

Chain of responsibility

Recognizeable by behavioral methods which (indirectly) invokes the same method in another implementation of same abstract/interface type in a queue

Command

Recognizeable by behavioral methods in an abstract/interface type which invokes a method in an implementation of a different abstract/interface type which has been encapsulated by the command implementation during its creation

Interpreter

Recognizeable by behavioral methods returning a structurally different instance/type of the given instance/type; note that parsing/formatting is not part of the pattern, determining the pattern and how to apply it is

Iterator

Recognizeable by behavioral methods sequentially returning instances of a different type from a queue

Mediator

Recognizeable by behavioral methods taking an instance of different abstract/interface type (usually using the command pattern) which delegates/uses the given instance

Memento

Recognizeable by behavioral methods which internally changes the state of the whole instance

Observer (or Publish/Subscribe)

Recognizeable by behavioral methods which invokes a method on an instance of another abstract/interface type, depending on own state

State

Recognizeable by behavioral methods which changes its behaviour depending on the instance's state which can be controlled externally

Strategy

Recognizeable by behavioral methods in an abstract/interface type which invokes a method in an implementation of a different abstract/interface type which has been passed-in as method argument into the strategy implementation

Template method

Recognizeable by behavioral methods which already have a "default" behaviour definied by an abstract type

Visitor

Recognizeable by two different abstract/interface types which has methods definied which takes each the other abstract/interface type; the one actually calls the method of the other and the other executes the desired strategy on it


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