行遠自邇，登高自卑

行遠必自邇，登高必自卑

a journey of a thousand miles begins with a single step

SOLID Design

SOLID Object Oriented Design Principles

S	SRP	Single responsibility principle the notion that an object should have only a single responsibility.
O	OCP	Open/closed principle the notion that “software entities … should be open for extension, but closed for modification”.
L	LSP	Liskov substitution principle the notion that “objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program”. See also design by contract.
I	ISP	Interface segregation principle the notion that “many client specific interfaces are better than one general purpose interface.”[5]
D	DIP	Dependency inversion principle the notion that one should “Depend upon Abstractions. Do not depend upon concretions.”[5] Dependency injection is one method of following this principle.