设计模式（一）——概述(Overview)

最近在上课和考试都遇到很多设计模式方面的问题，所以决定在网上学习一下相关的知识，免得以后碰到又不会了。

一、设计模式

设计模式(Design pattern)是一套被反复使用、多数人知晓的、经过分类编目的、代码设计经验的总结。使用设计模式是为了可重用代码、让代码更容易被他人理解、保证代码可靠性。 毫无疑问，设计模式于己于他人于系统都是多赢的；设计模式使代码编制真正工程化；设计模式是软件工程的基石脉络，如同大厦的结构一样。

二、设计原则

开闭原则(Open Closed Principle):S oftware entities (classes, modules, functions, etc.) should be open for extension, but closed for modification.

里氏代换原则(Liskov Substitution Principle):In a computer program, if S is a subtype of T, then objects of type T may be replaced with objects of type S (i.e., objects of type S may substitute objects of type T) without altering any of the desirable properties of that program (correctness, task performed, etc.).

依赖倒转原则(Dependency Inversion Principle):The conventional dependency relationships established from high-level, policy-setting modules to low-level, dependency modules are inverted (i.e. reversed), thus rendering high-level modules independent of the low-level module implementation details.

接口隔离原则(Interface Segregation Principle):No client should be forced to depend on methods it does not use.

合成/聚合复用原则(Composite/Aggregate Reuse Principle):Composite/Aggregate Reuse Principle(CARP) or Composite Reuse Principle(CRP) which is using existed object in new object to make it a part of new object;To reuse already existed function the new object delegate to those obgect.

最小知识原则(Principle of Least Knowledge):A given object should assume as little as possible about the structure or properties of anything else (including its subcomponents), in accordance with the principle of "information hiding".

三、基本模式

创建型模式：单例模式、抽象工厂模式、建造者模式、工厂模式、原型模式。

结构型模式：适配器模式、桥接模式、装饰模式、组合模式、外观模式、享元模式、代理模式。

行为型模式：模版方法模式、命令模式、迭代器模式、观察者模式、中介者模式、备忘录模式、解释器模式、状态模式、策略模式、职责链模式、访问者模式。