自己一个人磕盐写项目，写着写着感觉自己代码架构混乱不忍直视。 想起来自己在读CS的时候同学推荐过《Head First设计模式》这本书。 于是从图书馆借来读，收获颇丰。这里记录了读书时的一些笔记。
设计模式领域有两本非常有名的书：
- Head First Design Patterns - Eric Freeman, Elisabeth Freeman, Kathy Sierra, Bert Bates
- Design Patterns - Eric Gamma, Richard Helm, Ralph Johnson, JHohn Vlissides
我现在只读了第一本，之后便尝试将自己所学应用到代码中去，有机会我会读第二本。
OO Basics - 基础
- 抽象 Abstraction
- 封装 Encapsulation
- 多态 Polymorphism
- 继承 Inheritance
OO Principles - 原则
* 封装变化 Encapsulate what varies.
* 多用组合，少用继承 Favor composition over inheritence.
* 针对接口编程，不针对实现编程 Program to interfaces, not to implementations.
* 为交互对象之间的松耦合设计而努力 Strive for loosely coupled designs between objects that interact
* 类应该对扩展开放，对修改关闭 Classes should be open for extension but closed for modification.
* 依赖抽象，不要依赖具体类 Depend on abstractions. Do not depend on concrete classes.
* 只和朋友交谈 Only talk to your friends.
* 超类主控一切，需要的时候自然会调用子类 Don't call us, we call you.
* 类只能有一个改变的理由(利用代理控制访问) A class should have only one resason to change.
OO Patterns - 模式
| Patterns | Description |
|---|---|
| 策略模式 | Strategy - defines a family of algorithms, encapsulates each one, and makes them interchangeable, Stragy lets the algorithm vary independently from clients that use it. |
| 观察者模式 | Observer - defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically |
| 装饰者模式 | Decorator - Attach additional responsibilities to an object dynamically. Decorators porvide a flexible alternative to subclassing for extending functionality. |
| 工厂模式 | Abstract Factory - Provide an interface for creating families of related or depedent objects without specifying their concrete classes. Factory Method - Define an interface for creating an object, but let subclass decide which class to instantiate. Factory Method lets a class defer instantiation to the subclass. |
| 单件模式 | Singleton - Ensure a class only has one instance and provide a global point of access to it. |
| 命令模式 | Command - Encapsulates a request as an object, thereby letting you parameterize clients with different request, queue or log requests, and support undoable operations. |
| 适配器模式 外观模式 |
Adapter - Converts the interface of a class into another interface clients expect. Let classes work together that couldn’t othervise because of incompatible interfaces. Facade - Provides a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use. |
| 模版方法模式 | 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. |
| 迭代器与组合模式 | Iterator - Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation. Composite - Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual ovjects and compositions of objects uniformly |
| 状态模式 | State -Allow an object to alter its behavior when its internal state changes. The object will appear to change its class. |
| 代理模式 | Proxy - Provide a surrogate or placeholder for another object to control access to it. |
| 复合模式 | Compoud Patterns - A Compound Pattern combines two or more patterns into a solution that solves a recurring or general problem. |
杂记
delegation（委派）的几种类型归纳: * Use (A use B) * Composition/aggregation (A owns B) * Association (A has B)
下图是一个书中的例子：
