SOLID and its relationship with OOP

SOLID is like the “5 rules” to write good OOP code. Not just working code, but clean and maintainable code.

S — Single Responsibility Principle (SRP)

A class should have only one reason to change. Each class, module, or function should handle only one responsibility. When a class has multiple reasons to change, it becomes fragile and tightly coupled.

O — Open/Closed Principle (OCP)

Software entities should be open for extension, but closed for modification. You should be able to add new functionality without changing existing code.

L — Liskov Substitution Principle (LSP)

A child class should fully replace its parent without breaking anything.

I — Interface Segregation Principle (ISP)

Don’t force classes to depend on things they don’t use. It’s better to have many small, specific interfaces than one large, general one.

D — Dependency Inversion Principle (DIP)

High-level modules (business logic) should not depend on low-level modules (e.g., database drivers).
Both should depend on abstractions (interfaces or abstract classes).

SOLID Principle	What it Means	Relation to OOP
S — Single Responsibility	One class = one job only.	Keeps objects focused and simple (Encapsulation).
O — Open/Closed	Open for extension, closed for modification.	Add new features without changing old code (Inheritance & Polymorphism).
L — Liskov Substitution	A child class should fully replace its parent without breaking anything.	Keeps Inheritance safe and logical.
I — Interface Segregation	Specific interfaces rather than one large, general one.	Encourages cleaner Abstraction.
D — Dependency Inversion	Depend on abstractions, not concrete implementations.	Promotes flexible and testable design (Abstraction & Encapsulation).