Low-Level Design Guide

Good architecture is built on a foundation of solid low-level design. This series is a deep dive into the "micro" side of software engineering—focusing on class design, object-oriented principles (SOLID), and tactical design patterns. We explore how to translate requirements into clean, maintainable code, handle concurrency at the component level, and define clear interfaces. Whether you're preparing for LLD interviews or looking to sharpen your day-to-day coding craftsmanship, this guide provides the blueprints for building modular software.

8 articles·~173 min total·Updated Mar 9, 2026

You're staring at an LLD interview question: "Design a parking lot system." You know OOP theory, but translating real-world problems into clean class hierarchies feels like a different skill entirely. The interviewer wants SOLID principles, design patterns, and interface contracts — but where do you even start?

The gap between knowing OOP concepts and applying them in interview scenarios is where most engineers stumble. This roadmap bridges that gap through a decision-tree approach: eight carefully sequenced problems that build OOP design fluency from state machines to production-grade implementations in Java Spring Boot.

TLDR: Follow the decision tree to find your learning path through 8 LLD problems, from OOP foundations to production systems, based on your timeline and interview focus.