Hello friend, If you have read hundreds of articles and even watched a lot of videos but still confused about SOLID. Help me help you. You are in safe hands. What are SOLID principles SOLID principles help write maintainable, testable code. These principles were initially pointed out by Robert C. Martin a.k.a. "Uncle Bob". If you have not watched his lectures, I would highly suggest to go on YouTube and watch, those are pure fun and knowledge. Now let's go over each of these principles. I will try to write examples that are more real in terms of software usage (no more Bike extending Vehicle class, no offense to anyone 😊). Single Responsibility Principle "A class should have one, and only one, reason to change." ❌ Bad Example: The "Do-It-All" Controller This Spring controller handles HTTP routing, manual SQL execution, external API payments, and email alerts. If your database schema or your email provider changes, this class breaks.…