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Learn object-oriented design and design patterns, solve low-level design cases, and practise state transitions, persistence and error handling in real repositories and code reviews.
This LLD learning path develops practical software design skills from object modeling to production-ready architecture decisions.
What you'll learn: • OOP and UML fundamentals • SOLID and essential design principles • Creational, structural, and behavioral patterns • API, persistence, and caching design • Concurrency and resource management • End-to-end LLD case studies
What Is Low-Level Design?
LLD vs HLD: Understanding the Design Spectrum
Why Low-Level Design Matters in Software Engineering
The LLD Mindset — Thinking in Components
LLD in Interviews vs Real-World Projects
Prerequisites & Learning Path
Why We Need Design Diagrams
UML Overview — The Standard Language
Class Diagrams — Structure Representation
Relationships: Association, Aggregation, Composition
Sequence Diagrams — Behavior Over Time
Use Case Diagrams — Requirements Capture
Activity & State Diagrams — Overview
When to Use Which Diagram
What Is a Class? What Is an Object?
Attributes and Methods
Constructors and Object Lifecycle
Access Modifiers and Visibility
Static vs Instance Members
Object Identity, Equality, and Hashing
Designing Clean Classes: The Art of Well-Structured Object-Oriented Code
What Is Inheritance?
The IS-A Relationship: When and Why to Use Inheritance
Method Overriding
The super Keyword and Chain Calls
Designing Sound Inheritance Hierarchies
When Inheritance Goes Wrong
Abstract Classes — Incomplete Contracts and Partial Implementations
What Is Polymorphism?
Compile-Time vs Runtime Polymorphism
Method Overloading
Method Overriding — The Engine of Runtime Polymorphism
Polymorphism Through Interfaces
The Power of Programming to Interfaces
Polymorphism Patterns in Practice
Revisiting Inheritance Problems
What Is Composition?
HAS-A vs IS-A Relationships
Favor Composition Over Inheritance — The Critical Design Choice
Delegation Pattern — Flexible Object Collaboration
When to Use Inheritance vs Composition — Making the Right Choice
Refactoring from Inheritance to Composition
Design a Parking Lot System
Design a Library Management System
DRY — Don't Repeat Yourself
KISS: Keep It Simple, Stupid
YAGNI — You Aren't Gonna Need It
Law of Demeter
The Principle of Least Astonishment (POLA)
Tell, Don't Ask Principle
Separation of Concerns
Cohesion and Coupling
Factory Method Pattern
Abstract Factory Pattern
Builder Pattern
Prototype Pattern: Object Cloning for Efficient Creation
Singleton Pattern
Object Pool Pattern — Recycling Resources for Performance
Choosing the Right Creational Pattern
Design a Vending Machine
Design a Coffee Vending Machine
Adapter Pattern — Bridging Incompatible Interfaces
Bridge Pattern
Composite Pattern
Decorator Pattern
Facade Pattern: Simplifying Complex Subsystems
Flyweight Pattern: Efficient Object Sharing
Proxy Pattern
Choosing the Right Structural Pattern
Strategy Pattern
Observer Pattern
Command Pattern: Encapsulating Requests as Objects
State Pattern
Template Method Pattern
Iterator Pattern: Uniform Collection Traversal
Design a Logging Framework
Design a Traffic Signal Control System
Design a Task Management System
Chain of Responsibility Pattern
Mediator Pattern: Centralizing Complex Interactions
Memento Pattern: State Preservation and Recovery
Visitor Pattern: Adding Operations Without Modifying Classes
Interpreter Pattern (Overview)
Null Object Pattern: Eliminating Null Reference Chaos
Choosing the Right Behavioral Pattern
Design an ATM
Design Tic Tac Toe Game
Design a Snake and Ladder Game
Dependency Injection Revisited
Constructor Injection: The Preferred DI Technique
Setter Injection: Providing Dependencies Through Mutator Methods
Interface Injection
Service Locator vs Dependency Injection
IoC Container Deep Dive
Lifetime Management in Dependency Injection
DI Anti-Patterns and Best Practices
Why Concurrency Matters
Threads and Processes
Thread Safety
Synchronization Primitives: Coordinating Concurrent Access
Deadlocks and Prevention
Atomic Operations: The Indivisible Units of Concurrency
Design Concurrent HashMap
Design Multi-threaded Merge Sort
Producer-Consumer Pattern
Thread Pool Pattern
Read-Write Lock Pattern
Future and Promise Pattern
Double-Checked Locking Pattern
Immutable Objects for Concurrency
Active Object Pattern
Design Thread-Safe Blocking Queue
Design an Elevator System
Introduction to Domain-Driven Design
Entities in Domain-Driven Design
Value Objects in Domain-Driven Design
Aggregates: Modeling Consistency Boundaries
Repositories
Domain Events
Domain Services in Domain-Driven Design
Bounded Contexts
Design a Car Rental System
Design a Hotel Management System
Design a Digital Wallet Service
Design a Restaurant Management System
Why Architecture Matters
Traditional Layered Architecture
Hexagonal Architecture (Ports & Adapters)
Onion Architecture: Domain-Centric System Design
Clean Architecture
Choosing an Architecture
Package and Module Organization
Persistence Layer Responsibilities
Repository Pattern Deep Dive
Data Access Object (DAO) Pattern
Unit of Work Pattern
Object-Relational Mapping Considerations
Data Modeling for Low-Level Design
Database Transactions at LLD Level
An unsuccessful credit capture changes account balances
Capture reserved credit only once
Errors vs Exceptions: Foundations of Robust Error Handling
Exception Hierarchy Design
Checked vs Unchecked Exceptions
Error States and Result Types
Exception Handling Best Practices
Validation and Defensive Programming
Error Handling at Boundaries
Failed release journals leave a partially published room
Isolate the editorial transaction draft
Why Testing Matters for Low-Level Design
Unit Testing Fundamentals
Test Doubles: Mocks, Stubs, Fakes
Mocking Dependencies in Object-Oriented Testing
Test-Driven Development (TDD)
Testing Private Methods and Internals
Integration Testing at LLD Level
Code Coverage and Test Quality
Temporary access remains valid at its expiry time
Expire access at the deadline
Case Study: Parking Lot System Design
Library Management System
Elevator System Design
Chess Game - Low Level Design
Case Study: Ride-Sharing Service Design
Hotel Booking System
Design Stack Overflow
Design LinkedIn
Design an Online Auction System
Design an Airline Management System
Design Facebook
Design a Concert Ticket Booking System
Design CricInfo
Design Splitwise
Design a Chess Game
Design Uber
Design a Course Registration System
Design a Movie Ticket Booking System
Design Amazon
Design Zerodha
Design Spotify
Design Swiggy
What Interviewers Look For in LLD Interviews
Time Management in LLD Interviews
Clarifying Requirements in LLD Interviews
Communicating Your Design
Handling Constraints & Trade-offs in LLD Interviews
Common LLD Interview Problems
From Design to Code
Code Organization & Structure
Refactoring Toward Better Design
Continuous Learning in Low-Level Design
Complete this path to earn a personalised certificate. You choose whether to make it public.