What Do SOLID Principles Stand For? Can You Give Examples?

SOLID Principles

S — Single Responsibility Principle

A class should have only one reason to change

• Bad: User class handles business logic, database access, and email sending
• Good: Split into User, UserRepository, EmailService

O — Open/Closed Principle

Open for extension, closed for modification

• Add new features without modifying existing code; use inheritance/composition
• Strategy Pattern is a classic implementation

L — Liskov Substitution Principle

Subclasses must be substitutable for their base class without breaking behavior

• Violation: Square extends Rectangle—setting width also sets height, breaking rectangle semantics

I — Interface Segregation Principle

Don't force clients to depend on interfaces they don't use; split large interfaces into small, specific ones

D — Dependency Inversion Principle

High-level modules shouldn't depend on low-level modules; both should depend on abstractions (interfaces)

• Dependency Injection (DI) is the common technique to apply this principle