SOLID

SOLID is a mnemonic acronym for five design principles intended to make software designs more understandable, flexible and maintainable. The principles are a subset of many principles promoted by American software engineer and instructor Robert C. Martin.

Single responsibility principle

A class should only have a single responsibility, that is, only changes to one part of the software's specification should be able to affect the specification of the class.

Open–closed principle

"Software entities ... should be open for extension, but closed for modification."

Liskov substitution principle

"Objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program."

Interface segregation principle

"Many client-specific interfaces are better than one general-purpose interface."

Dependency inversion principle

One should "depend upon abstractions, [not] concretions."