A class should have one and only one reason to change, meaning that a class should only have one job.
Define responsibilities
Strive for high chohesion and loose coupling
Keep classses small, focused, testable
Open Closed
Objects or entities should be open for extension, but closed for modification.
Open for extension means that we should be able to add new features or components to the application without breaking existing code.
Closed for modification means that we should not introduce breaking changes to existing functionality, because that would force you to refactor a lot of existing code
Balance abstraction and concreteness. Abstraction adds complexity. Predict where variation is needed and apply abstraction as needed.
When you use new keyword, you are being concrete. new is glue. Dependency Injection..
Implement new features in new classes. In this way, you can add behavior without touching existing code.
Liskov Substitution Principle
Objects of a superclass shall be replaceable with objects of its subclasses without breaking the application.
Subtypes must be substitutable for their base types.
Tell, Don’t Ask: Rather than asking an object for data and acting on that data, we should instead tell an object what to do.
Interface Segregation
A client should not be forced to implement an interface that it doesn’t use.
A clien shouldn’t be forced to depend on methods they do not use.
Split interfaces in behaviours. I….able interface.
Dependency Inversion
High level modules should not depend on low level modules. Both should depend on abstractions.
Entities must depend on abstractions not on concretions.
