 | Gang of Four Design Patterns
The Gang of Four are the four authors of the book, "Design Patterns: Elements of Reusable Object-Oriented Software". In this article their twenty-three design patterns are described with links to UML diagrams, source code and real-world examples for each. |
| Visitor Design Pattern
The visitor pattern is a design pattern that separates a set of structured data from the functionality that may be performed upon it. This promotes loose coupling and enables additional operations to be added without modifying the data classes. |
| Command Design Pattern
The command pattern is a design pattern that enables all of the information for a request to be contained within a single object. The command can then be invoked as required, often as part of a batch of queued commands with rollback capabilities. |
| Mediator Design Pattern
The mediator pattern is a design pattern that promotes loose coupling of objects by removing the need for classes to communicate with each other directly. Instead, mediator objects are used to encapsulate and centralise the interactions between classes. |
| Interpreter Design Pattern
The interpreter pattern is a design pattern that is useful when developing domain-specific languages or notations. The pattern allows the grammar for such a notation to be represented in an object-oriented fashion that can easily be extended. |
| Iterator Design Pattern
The iterator pattern is a design pattern that provides a means to for the elements of an aggregate object to be accessed sequentially without knowledge of its structure. This allows traversing of lists, trees and other structures in a standard manner. |
| State Design Pattern
The state pattern is a design pattern that allows an object to completely change its behaviour depending upon its current internal state. By substituting classes within a defined context, the state object appears to change its type at run-time. |
| Template Method Design Pattern
The template method pattern is a design pattern that allows a group of interchangeable, similarly structured, multi-step algorithms to be defined. Each algorithm follows the same series of actions but provides a different implementation of the steps. |
| Memento Design Pattern
The memento pattern is a design pattern that permits the current state of an object to be stored without breaking the rules of encapsulation. The originating object can be modified as required but can be restored to the saved state at any time. |
| Chain of Responsibility Design Pattern
The chain of responsibility pattern is a design pattern that defines a linked list of handlers, each of which is able to process requests. When a request is submitted to the chain, it is passed to the first handler in the list that is able to process it. |