Design Patterns

Design patterns are typical solutions to common problems in software design. This repository contains 22 of the Gang of Four's patterns.

Creational

Patterns that flexibly create and instantiate objects.

Abstract Factory groups object factories that have a common theme.
Builder constructs complex objects by separating construction and representation.
Factory Method creates objects without specifying the exact class to create.
Prototype creates objects by cloning an existing object.
Singleton restricts object creation for a class to only one instance.

Patterns that define ways to compose objects to obtain new functionality.

Adapter allows classes with incompatible interfaces to collaborate.
Bridge decouples an abstraction from its implementation so that the two can vary independently.
Composite composes zero-or-more similar objects so that they can be manipulated as one object.
Decorator dynamically adds/overrides behaviour in an existing method of an object.
Facade provides a simplified interface to a complex system of classes, library or framework.
Flyweight reduces the cost of creating and manipulating a large number of similar objects.
Proxy provides a placeholder for another object to control access, reduce cost, and reduce complexity.

Patterns that specifically concern the communication and the assignment of responsibilities between objects.

Chain of Responsibility delegates commands to a chain of processing objects.
Command converts request into a object which encapsulates actions and parameters.
Iterator accesses the elements of an object sequentially without exposing its underlying representation.
Mediator allows loose coupling between classes by being the only class that has detailed knowledge of their methods.
Memento provides the ability to restore an object to its previous state (undo).
Observer is a publish/subscribe pattern which allows a number of observer objects to see an event.
State allows an object to alter its behavior when its internal state changes.
Strategy allows one of a family of algorithms to be selected on-the-fly at runtime.
Template Method defines the skeleton of an algorithm as an abstract class, allowing its subclasses to provide concrete behavior.
Visitor separates an algorithm from an object structure by moving the hierarchy of methods into one object.