这本书应该是我目前为止读过的最有趣的一本书, 里面是多插图, 言语幽默 , 而且里面还经常采用拟人的手法,比如说Abstract Factory 和 Factory Method 模式之间的对话,当然了,这并不是说讲的深度不够,恰恰相反,他把问题说的非常透彻.
这本书和我以前所看过的计算机书籍有很大的不同, 它同时以一个读书笔记又或者说以黑板式的教学方式来说. 其实呢, 我想说的是, 我在看这本书的时候并不是感觉在看书, 而是感觉坐在教室里听课. 真的, 如果我有机会教授Design Pattern的课程, 这本书是我的首选课本!! (感觉我在卖这本书的广告??不妨告诉你个秘密, 我真的没收到这本书的任何小费.)
如果用简单一句话来表达读完这本书的感受,我想说的是,”不知道内地什么时候出这本书的影印版,我好去买”.(买不起原版的人含泪说道.)
下面是以我的理解来说设计模式和理解这本书.
设计模式其实是一个产物,是什么的产物呢? 是运用OO原则解决某个具体问题(Context)的产物. 那么OO原则是什么东西呢? OO原则也是一个产物? 那又是什么的产物呢? 是为了以后能更容易扩展代码,使得软件更容易维护. 大家就是为了更容易达到这个目的而总结出来的一些经验.
俗话说:”攻城容易,守城难!”, 写个软件容易, 但要长时间的维护这个软件来适应需求等,那就难了.
我们就从OO具有哪些特性(OO Basic) 以及OO的一些原则 (OO Principle),来看设计模式是如何应用OO Basic来实现一些 OO Principle.
1.1. OO Basic
· Abstraction
· Inheritance
· Polymorphism
· Encapsulation
1.2. OO Principle
· Identify the aspect of your application that vary and separate them from what stays the same.
· Program to an interface, not an implementation.
· Favor composition over inheritance.
· Strive for loosely coupled designs between objects that interact.
· Classes should be open for extension but closed for modification.
· Depend on Abstraction. Do not depend on concrete classes.
· Principle of Least knowledge – talk only to your immediate friends.
· Don’t call us, we will call you.
· A class should have one reason to change.
1.3. Design Patterns
1.3.1. Strategy Pattern
Defines a family of algorithms, encapsulates each one, and make them interchangeable. Strategy lets the algorithm vary independently from client that uses it.
1.3.2. Observer
Defines a one-to-many dependency between objects so that when object change state, all its dependents are notified and updated automatically.
1.3.3. Decorator
Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
1.3.4. Abstract Factory
Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
1.3.5. Factory Method
Define an interface for creating an object, but let subclass decide which class to instantiate. Factory Method let a class defer instantiation to the subclass.
1.3.6. Singleton
Ensure a class only has one instance and provide a global point of access to it.
1.3.7. Command
Encapsulates a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.
1.3.8. Adapter
Converts the interface of a class into another interface the client expects. Adapter lets classes work together that couldn’t otherwise because of incompatible interfaces.
1.3.9. Facade
Provides a unified interface to a set of interface in a subsystem. Façade defines a higher-level interface that makes the subsystem easier to use.
1.3.10. 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.
1.3.11. Iterator
Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
1.3.12. Composite
Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and composition of objects uniformly.
1.3.13. State
Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.
1.3.14. Proxy
Provide a surrogate or placeholder for another object to control access to it.