Low-Level Design (LLD) Roadmap
Master object-oriented design, design patterns, and LLD interview problems
For High-Level Design (HLD)
This roadmap covers Low-Level Design. For system architecture, scalability, and distributed systems, see:
Your Journey at a Glance
This roadmap is fully written up — 46 in-depth guides
Every phase below links to its own guides: full explanations, diagrams and worked examples, not just a list of topics to go and find elsewhere.
OOP Foundations & SOLID
Build unshakeable object-oriented fundamentals. Understand not just how to write classes, but how to design systems that are easy to change, test, and extend.
Creational Design Patterns
Patterns for object creation. Not just how to instantiate objects, but how to decouple your system from the specifics of what gets created, how it gets created, and when.
Structural Design Patterns
Patterns for composing classes and objects into larger structures. These patterns make it easier to assemble systems from independent parts while keeping them decoupled.
Behavioral Design Patterns
Patterns for communication between objects. These patterns define how objects interact, distribute responsibility, and encapsulate behavior. This is where most LLD interview solutions live.
Schema & API Design
The bridge between object design and system design. Master database schema design, REST/gRPC contract design, and the interface contracts that connect your well-designed components to the outside world.
LLD Interview Problems
The core of LLD interview preparation. Each problem follows the same framework: gather requirements → identify actors → define use cases → design classes → apply patterns → discuss trade-offs. Practice drawing class diagrams and explaining your design out loud.
Roadmap Complete!
You now have the foundations of a production-ready Java engineer. Apply by building real projects.
Design a Complete Online Food Ordering Platform
Design a full-featured food ordering system (Swiggy/UberEats-style) at the LLD level. Define all classes, interfaces, relationships, and design patterns. Cover: restaurant management, menu/catalog, cart, order processing, payment, delivery assignment, real-time order tracking, ratings & reviews, and promotion/coupon system.
What you'll build
- Class diagram with 30+ entities and their relationships
- Order state machine: cart → placed → confirmed → preparing → picked up → delivered → completed
- Cart management with item customization (toppings, add-ons, quantity)
- Restaurant menu with categories, items, variants, and availability
- Pricing strategy: base price + taxes + delivery fee + discounts (strategy pattern)
- Coupon/discount system with validation rules (minimum order, user-specific, expiry)
- Delivery partner assignment algorithm (nearest available, capacity-aware)
- Rating & review system (restaurant-level and delivery-partner-level)
- Real-time order tracking (observer pattern for status notifications)
- Payment processing with idempotent transactions (saga for distributed commit)
Tech stack
Key highlights
- ✦Demonstrates mastery of 8+ design patterns applied in one cohesive system
- ✦Covers the full spectrum: data modeling, state machines, strategy patterns, observer notifications, saga transactions
- ✦Portfolio-worthy artifact that proves you can design production-grade software at the class level