Java low-level design archive

Learn LLD by building,
one question at a time.

A personal knowledge base for low-level design problems, design patterns, tradeoffs, Java code, and lessons learned while practicing.

Questions

Language

Java

Practice index

LLD Questions

Each question includes requirements, entities, design patterns, important Java snippets, what I learned, and future improvements.

Medium

Design a parking lot with floors, typed spots, vehicle allocation, ticketing, and fee calculation.

Medium

Design a vending machine with inventory, payments, item selection, dispensing, and change return.

Hard

Design an elevator system with buildings, multiple elevators, floor requests, internal requests, dispatching, and movement strategies.