Low-Level Design for MAANG Interviews

A book-shaped table of contents for LLD interview prep: OOP fundamentals through SOLID, design principles, UML, design patterns, dependency management, reliability, concurrency, domain modeling, API design, testing, refactoring, classic interview problems, advanced architecture, and performance — cross-linking Object-Oriented Programming and Patterns instead of duplicating them.

1 — Refactoring Techniques

Surveys the catalog of small, behavior-preserving transformations used to improve code structure without changing external behavior.

3 — Replace Conditional with Polymorphism

Explains replacing branching type-checks with polymorphic dispatch so new cases extend the code rather than modify a growing switch statement.

4 — Extract Object

Covers pulling a cohesive group of fields and behavior out of a bloated class into a new, focused collaborator.

5 — Introduce Parameter Object

Explains grouping a repeated cluster of parameters into a single object to reduce signature churn and clarify caller intent.