#oop

Explain the "Single Responsibility Principle" (SRP) from the SOLID principles of object-oriented design. Provide a simple "before" code example in C# or Java that violates SRP, and then show an "after" example that refactors the code to adhere to the principle.

Apply design patterns to solve common problems. Creational: 1. Singleton (single instance). 2. Factory (object creation). 3. Builder (complex object construction). Structural: 4. Adapter (interface compatibility). 5. Decorator (add behavior dynamically). 6. Facade (simplified interface). Behavioral: 7. Observer (event notification). 8. Strategy (interchangeable algorithms). 9. Command (encapsulate requests). 10. Template Method (algorithm skeleton). Don't force patterns - use when appropriate. Understand problem first. Patterns improve communication ('let's use Observer here'). Study Gang of Four book. Practice with real examples.