# Object-Oriented Design Principles - SOLID Who gets asked Low Level Design questions?\ Almost every leading payer (product company) has LLD rounds now, even freshers sometimes have LLD rounds.\ Companies: Amazon, Microsoft, Google & leading startups. \ What is Low Level Design?\ Low Level Design (LLD), also known as Object Oriented Design (OOD), is a detailed description of all components, configurations, and processes of the software.\ Low Level Design focuses on the class-level design of a software and clean, fast, readable, maintainable, and extensible code. **The Expectations of LLD interviews** An LLD Interview evaluates your skill on creating modular, flexible, maintainable and reusable software, by applying Object-oriented Design Principles and Design Patterns. LLD questions like, ***Design a Parking Lot,*** ***Design a Tic-tac-toe Game,*** ***Design a Ticketing System*** ***...*** in the **class-level**, are intentionally unstructured and open-ended and they don't have a standard answer. **How to Prepare for the LLD Interview** 1. Learn an object-oriented language ( C++ / Java / Python or C# ) 2. Study about the **SOLID** and other Object Oriented Principles 3. Learn all the common **Design Patterns** and their applications 4. Explore some open-source projects and try to understand the best practices 5. Practice common LLD interview questions LLD Principles The object-oriented design principles are also called **SOLID**. The main goal of these principles is to make software resilient to changes and easy to extend and maintain...