SOLID Principles (A Simple Version)

S - Single Responsibility

• One class = one job • Each class should have only one reason to change

O - Open/Closed

• Open for extension, closed for modification • Add new features without changing existing code

L - Liskov Substitution

• Child classes should work wherever parent classes work • Subtypes must be substitutable for their base types

I - Interface Segregation

• Many small, specific interfaces > few large, general ones • Don't force classes to implement methods they don't need

D - Dependency Inversion

• Depend on abstractions, not concrete implementations • High-level modules shouldn't depend on low-level modules