OOP principles, SOLID, UML, and the design principles that everything else builds on.

The basics every LLD interview assumes you already know. Read top-to-bottom or jump to the topic you need.

Encapsulation, inheritance, polymorphism, abstraction

The five design principles

Overview before diving in

Class, sequence, state diagrams for interviews

Three rules that keep code small

When extends helps and when it hurts

Two metrics that predict code health

Finished reading?

Mark it done to track your progress in Designs.

Foundations