2) 单一职责原则 (The Single Responsiblity Principle,简称SRP)
3) 里氏替换原则(The Liskov Substitution Principle,简称LSP)
4) 依赖倒置原则(The Dependency Inversion Pricinple,简称DIP)
5) 接口隔离原则 (The Interface Segregation Principle,简称ISP)
7) 组合优先于继承