What is Low-Level Design (LLD)?
While System Design (HLD) focuses on servers and databases, LLD focuses on the internal code structure. It is about how classes, interfaces, and objects interact to solve a problem without creating a "spaghetti" mess.
1. The Goal of LLD: Managing Change
The hallmark of a great LLD is that adding a new feature requires zero modification to existing code. This is achieved by mastering the SOLID Principles.
2. Curriculum in this Module
- Theory & Intuition (Current Page)
- Lesson: SOLID in Practice - Real production violations and fixes.
- Lesson: Object-Oriented Modeling - Designing classes for a Parking Lot.
- Curated Practice Problems - 10 essential LLD challenges.
3. The LLD Interview Process
We use the REQUIRE framework:
- Requirements: Clarify the scope (e.g., "Just cars, or motorcycles too?").
- Entities: Identify the main classes (e.g.,
Vehicle,Slot,Floor). - Quality: Define the interfaces and relationships (e.g.,
PaymentStrategy). - Unify: Build the class diagram.
- Implement: Write the core logic in Java.
- Refactor: Apply SOLID to clean it up.
- Evaluate: Discuss extensibility.
Final Takeaway
LLD is not about writing more code; it's about writing fewer, more focused classes.