LLD Practice

Low-Level Design practice problems implemented in Java, applying common OOP design patterns.

Projects

Project	Design Patterns
ATM	State, Chain of Responsibility, Strategy, Factory
Elevator	State, Command, Strategy
LRU Cache	— (Data Structures: Doubly Linked List + HashMap)
Logger	Chain of Responsibility, Singleton
Parking Lot	Strategy
SplitWise	Strategy, Factory
StackOverflow	Observer
Vending Machine	State, Strategy

Design Patterns Covered

• Creational: Factory, Singleton
• Behavioral: State, Strategy, Chain of Responsibility, Command, Observer
• Structural: —

Tech Stack

• Java (Maven projects)

Structure

Each project is a self-contained Maven module with the following layout:

<ProjectName>/
├── pom.xml
└── src/main/java/
    ├── entities/       # Domain models
    ├── enums/          # Enumerations
    ├── service/        # Business logic
    ├── strategy/       # Strategy implementations
    ├── state/          # State implementations
    └── <Project>Demo.java  # Entry point / demo runner