SOLID

SOLID is a mnemonic acronym for five design principles intended to make object-oriented designs more understandable, flexible, and maintainable.

The principles are a subset of many principles first introduced by Robert C. Martin in 2000th in the paper Design Principles and Design Patterns

• Single Responsibility Principle. srp.pdf

  There should never be more than one reason for a class to change.

  Update 2018. "Clean architecture: a craftsman's guide to software structure and design":

  A module should be responsible to one, and only one, actor.

• Open-Closed Principle.

  Original ocp

  Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification.

  Update 2014

  You should be able to extend the behavior of a system without having to modify that system.

• Liskov Substitution Principle. lcp

  Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it.

• Interface Segregation Principle. isp

  Clients should not be forced to depend upon interfaces that they do not use.

• Dependency Inversion Principle. dip

  A. High-level modules should not depend upon low-level modules. Both should depend upon abstractions.

  B. Abstractions should not depend upon details. Details should depend upon abstractions.