GOF The four authors Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides are collectively introduced Gang of Four Design Patterns in Software development. In 1994, they published a book (Design Patterns: Elements of Reusable Object-Oriented Software) for explaining the concept of Design Patterns.
Abstract Factory Creates an instance of several families of classes
Builder Separates object construction from its representation
Factory Method Creates an instance of several derived classes
Prototype A fully initialized instance to be copied or cloned
Singleton A class of which only a single instance can exist
Adapter Match interfaces of different classes
Bridge Separates an object’s interface from its implementation
Composite A tree structure of simple and composite objects
Decorator Add responsibilities to objects dynamically
Facade A single class that represents an entire subsystem
Flyweight A fine-grained instance used for efficient sharing
Proxy An object representing another object
Chain of Resp. A way of passing a request between a chain of objects
Command Encapsulate a command request as an object
Interpreter A way to include language elements in a program
Iterator Sequentially access the elements of a collection
Mediator Defines simplified communication between classes
Memento Capture and restore an object's internal state
Observer A way of notifying change to a number of classes
State Alter an object's behavior when its state changes
Strategy Encapsulates an algorithm inside a class
Template Method Defer the exact steps of an algorithm to a subclass
Visitor Defines a new operation to a class without change
Factory vs Abstract Factory Both Abstract Factory and Factory design pattern are creational design pattern and use to decouple clients from creating object they need, But there is a significant difference between Factory and Abstract Factory design pattern, Factory design pattern produces implementation of Products e.g. Garment Factory produce different kinds of clothes, On the other hand Abstract Factory design pattern adds another layer of abstraction over Factory Pattern and Abstract Factory implementation itself e.g. Abstract Factory will allow you to choose a particular Factory implementation based upon need which will then produce different kinds of products.
In short 1) Abstract Factory design pattern creates Factory
2) Factory design pattern creates Products
e.g. Designing authentication system for a product, Authentication factory gives object for authentication of particular type based on input. e.g. for Windows Authentication it will give Identity Auth, for OWIN it will corresponding type, for forms-authentication, it will gave corresponding type. If we want to decouple whole system from underlying authentication, Abstract factory can give Interface of Authentication Factory that can be replace by any one of authentication system without impacting Outer system
AbstractFactory : Declares an interface for operations that create abstract product objects.
ConcreteFactory : Implements the operations declared in the AbstractFactory to create concrete product objects.
Product : Defines a product object to be created by the corresponding concrete factory and implements the AbstractProduct interface.
Client : Uses only interfaces declared by AbstractFactory and AbstractProduct classes.