SOLID Principles

• Single Responsibility Principle
  • Each class should have only one responsibility or reason to change.
  • narrow down the behaviour a class can have
• Open-Closed Principle
  • Software entities should be open for extension but closed for modification.
  • to add new functionality to a class without changing the existing code by extending a class and adding new functions into subclass
• Liskov Substitution Principle
  • Objects of a superclass should be replaceable with objects of a subclass without affecting the correctness of the program.
  • a subclass should behave like its superclass, and any methods that the superclass has should also be valid for the subclass
  • if 2 classes implement the same interface, these 2 classes should be interchangable without breaking anything
• Interface Segregation Principle
  • Clients should not be forced to depend on interfaces they do not use.
  • If there is an interface that defines 5 functions and we only need 2 functions to implement, don’t implement this interface.
  • Instead, seperate the interface for their own purpose.
• Dependency Inversion Principle
  • High-level modules should not depend on low-level modules. Both should depend on abstractions.
  • don’t define the parameter as a class; instead, define an interface
  • it would be easy to be tested by passing a test class that implements the interface