Principles governing object-oriented programming (four pillars, SOLID and other)
Principles provide high level guidelines to design better software applications. OOP principles should be applied while designing application classes to achieve modularity, easier code maintainability, extensibility, greater flexibility and resilience to change.
These principles give high-level design guidelines but do not give implementation details. There are several possible ways to implement them. This repository demonstrates simple examples of such implementations.
Design patterns often implement these principles. (see rafkub/oop-design-patterns)