Object-Oriented Design: Beginner to Master

Welcome to the definitive guide to mastering low-level design (LLD). This curriculum is structured to take you from understanding basic objects to designing complex, concurrent systems.

Level 1: The Foundations

Before diving into code, you must master the "Why" and "How" of object relationships.

• Introduction: Why OOD matters in high-scale engineering.
• Fundamentals: OOP Pillars and SOLID Principles.
• The 4-Step Framework: A repeatable process for any OOD interview.

Level 2: Beginner Challenges

Focus on basic entities, simple state management, and clear class hierarchies.

• Tic-Tac-Toe: Board state and win logic.
• Vending Machine: Introducing the State Pattern.
• File System: Mastering the Composite Pattern.

Level 3: Intermediate Designs

Dealing with many-to-many relationships, inheritance vs. composition, and basic business logic.

• Parking Lot: Vehicle types and floor management.
• Library Management: Loans, fines, and reservations.
• Hotel Management: Room types and booking lifecycles.
• Car Rental System: Vehicle inventory and reservation rules.

Level 4: Mastery (Complex Systems)

These problems require handling concurrency, complex state transitions, and high-scale architecture.

• Movie Ticket Booking: Concurrency and atomic seat locks.
• ATM System: Secure transactions and state-driven UI.
• Chess Game: Complex inheritance and validation.
• Stack Overflow: Reputation systems and notifications.
• Online Shopping: Order lifecycles and payment strategies.
• Logistics System: Shipment tracking and route optimization.
• Social Network: User relations and notification engines.
• Instant Messaging: Real-time chat and group management.
• Food Delivery System: Multi-actor workflows (Customer, Restaurant, Driver).

Practice & Patterns

• Design Pattern Glossary: Quick reference for OOD interviews.

[!TIP] Don't skip the Framework! Even if you know the code, the process of requirement gathering is what interviewers value most.