In software engineering, SOLID is a mnemonic acronym for five design principles intended to make object-oriented designs more understandable, flexible, and maintainable.
The SOLID ideas are
The single-responsibility principle: "There should never be more than one reason for a class to change." In other words, every class should have only one responsibility.
The open–closed principle: "Software entities ... should be open for extension, but closed for modification."
The Liskov substitution principle: "Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it." See also design by contract.
The interface segregation principle: "Many client-specific interfaces are better than one general-purpose interface."
The dependency inversion principle: "Depend upon abstractions, [not] concretions."
理解
上面摘自维基百科，一句概括：SOLID是面向对象设计的五个原则，另软件更易理解，更灵活可维护。而在《架构简洁之道》中，作者展开并讨论了SOLID对于架构设计上的重要价值。很容易理解，架构设计中的组件、子系统，可以看做各种通过网络组织起来的对象，SOLID原则同样可以提高架构的可理解性，灵活性，可维护性。
