OOP - Dependency-Inversion Principle

重點：program to an interface,  not an implementation


原本上層的類別會依賴下層的類別，就如同要蓋二樓就必須蓋好一樓
但 Dependency-Inversion Principle 的意思就是應該要讓上層和下層都依賴於抽象層，也就是上面重點說的 interface



http://teddy-chen-tw.blogspot.com.au/2012/01/5dependency-inversion-principle.html