S.O.L.I.D. principle
The Single-responsibility principle: "There should never be more than one reason for a class to change."[5] In other words, every class should have only one responsibility.[6]
The Open–closed principle: "software entities ... should be open for extension, but closed for modification."[7]
The Liskov substitution principle: objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program. See also design by contract.[8]
The Interface segregation principle: "many client-specific interfaces are better than one general-purpose interface."[9][4]
The Dependency inversion principle: "depend upon abstractions, [not] concretions."[10][4]