OOAD(5): Design Principles

Avoid duplicate code

當發現重複的程式碼片斷時，通常代表「設計」有問題。例如責任放錯了類別，或者是否應該delegate到別的類別等等。

Encapsulate what varies

Code to an interface rather than an implementation

Each class in your should have only one reason to change

Classes are about behavior and fuctionlity

在系統中的每個物件只有單一的責任