What are design patterns in ASP .NET? Explain it.

Hi Sam,

Design patterns provide general solutions or flexible way to solve common software design problems.

"Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice."

                                                                      -- Christopher Alexander - A Pattern Language

The 23 Gang of Four (GoF) patterns are generally considered the foundation for all other patterns. They are placed in three groups: Creational, Structural, and Behavioral (for a complete list see below). 

Creational 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

Structural Patterns

• 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

Behavioral Patterns

• 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