0.1 Basic knowledge
 0.2 Basic Principle
  0.2.1 High cohension
  0.2.2 Loose coupling
 0.3 Design pattern
  0.3.1 Introduction
  0.3.2 Creational patterns
   Singleton
   Prototype
   Factory method
   Abstract Factory
   Builder
   Creational summary
  0.3.3 Structurtal patterns
   Adapter
   Bridge
   Composite
   Decorator
   Facade
   Proxy
   Flyweight
  0.3.4 Behavioral patterns
   Observer
   Mediator
   State
   Chain of responsibility
   Command
   Memento
   Iterator
   Visitor
   Interpreter
   Strategy
   Template method