𝗠𝗮𝘀𝘁𝗲𝗿 𝘁𝗵𝗲 𝗦𝗢𝗟𝗜𝗗 𝗣𝗿𝗶𝗻𝗰𝗶𝗽𝗹𝗲𝘀

If you’re preparing for tech interviews or aiming to write cleaner, scalable code — this post is for you.

“Explain SOLID principles” is one of the most frequently asked interview questions in software engineering.

🧩 S — Single Responsibility Principle (SRP)

➡ Every class or module should have one reason to change.

Example: A class handling both user login and email sending should be split — one for authentication, one for notifications.

🧩 O — Open/Closed Principle (OCP)

➡ Code should be open for extension, closed for modification.

Example: Instead of editing existing code to add a new payment method, add a new class that implements a common interface.

🧩 L — Liskov Substitution Principle (LSP)

➡ Subclasses should be replaceable for their parent classes without breaking functionality.

Example: If Bird has fly(), then Ostrich shouldn’t inherit from Bird since it can’t fly.

🧩 I — Interface Segregation Principle (ISP)

➡ Don’t force classes to implement methods they don’t need.

Example: Instead of one giant Worker interface, split it into Eater and Sleeper so each class implements only what it needs.

🧩 D — Dependency Inversion Principle (DIP)

➡ Depend on abstractions, not concretions.

Example: Instead of hardcoding a database connection, use an interface — so you can switch from MySQL to MongoDB easily.

Following SOLID makes your code cleaner, testable, and scalable — qualities every great developer (and interviewer!) looks for.

Which SOLID principle do you find hardest to apply in real-world projects — and why?