Why Design Patterns Matter?
Design patterns are proven templates for solving recurring software design problems. In an LLD interview, patterns are the "vocabulary" you use to communicate your architecture.
The Golden Rule: Never start with a pattern. Start with a problem, and let the pattern emerge as the cleanest solution.
1. Patterns we will cover
- Strategy Pattern: For interchangeable algorithms (e.g., Payment methods).
- Factory Pattern: For object creation logic (e.g., Notification types).
- Observer Pattern: For event-driven decoupling (e.g., Order updates).
- Decorator Pattern: For adding behavior without inheritance (e.g., Pizza toppings).
- Singleton Pattern: For shared resources (e.g., Connection pools).
2. Curriculum in this Module
- Theory & Patterns Overview (Current Page)
- Lesson: The Strategy Pattern - Decoupling behavior from context.
- Lesson: The Factory Pattern - Mastering complex object creation.
- Lesson: The Observer Pattern - Event-driven architecture.
- Curated Practice Problems - 10 pattern-matching challenges.
3. Pattern Recognition Table
| If you see... | Use this Pattern |
|---|---|
Multiple if-else for different behaviors |
Strategy |
| Complex logic to decide which class to instantiate | Factory |
| One change needing to trigger actions in 5 other services | Observer |
| Needing to add features to an object at runtime | Decorator |
Final Takeaway
Mastering patterns allows you to write code that is Open for Extension but Closed for Modification (OCP).