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# Wednesday, January 20, 2010

In software engineering (or computer science), a design pattern is a general repeatable solution to a commonly occurring problem in software design. A design pattern is not a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations. Object-oriented design patterns typically show relationships and interactions between classes or objects, without specifying the final application classes or objects that are involved. Algorithms are not thought of as design patterns, since they solve computational problems rather than design problems.

 

Design patterns can be classified in terms of the underlying problem they solve.

 

 

  Creational Patterns -- concern the process of object creation.

  Abstract Factory

Provide an interface for creating families of related or dependent objects without specifying their concrete classes.

 

 

  Builder

 Separates the construction of a complex object from its representation so that several different representations can be created, depending on the needs of the program.

 

  Factory Method

Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation

 

  Prototype

The Prototype pattern starts with an instantiated class and copies or clones it to make new instances. These instances can then be further tailored using their public methods.

 

  Singleton

The Singleton pattern is a class of which there can be no more than one instance. It provides a single global point of access to that instance.

 

 

  Structural Patterns -- describe how classes and objects can be combined to form larger structures.

  Adapter

Convert the interface of a class into another interface clients expect.

Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.

 

  Bridge

Decouple an abstraction from its implementation so that the two can vary independently.

 

  Composite

Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and Compositions of objects uniformly.

 

  Decorator

Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

 

  Facade

Provide a unified interface to a set of interfaces in a subsystem. Façade defines a higher-level interface that makes the subsystem easier to use.

 

  Flyweight

Use sharing to support large numbers of fine-grained objects efficiently.

  Proxy

Provide a surrogate or placeholder for another object to control access

to it.

 

  Behavioral Patterns -- characterize the ways in which classes or objects interact and distribute responsibility

  Chain of Resp.

Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it.

 

  Command

Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.

 

  Interpreter

Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.

 

  Iterator

Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

 

  Mediator

Define an object that encapsulates how a set of objects interact.

Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.

 

  Memento

Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.

 

  Observer

Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.

 

  State

Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.

 

  Strategy

Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

 

  Template Method

  Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.

 

  Visitor

  Represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates.

 

 

Wednesday, January 20, 2010 6:48:52 AM (GMT Standard Time, UTC+00:00)  #    Comments [0]   Interview Question .Net  | 
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