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SOLID Principles Study Note

Single Responsibility

  • 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.

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