code principles

layers

modules(abstraction of objects and operations that have different layers)

interfaces(hide the information of attributes and give caller a protection)

 

reuseble

 

典型错误：

1.在最顶层的代码操作最底层模块的属性。

2.反对使用子程序（函数），说影响性能。

ERROR。

interfaces is not just interfaces, it is a self-explanation of the programs.