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 — Exception Design

Looks at how to design exception hierarchies and error-signaling contracts so that failures are informative and recoverable rather than opaque.

2 — Validation Strategies

Surveys strategies for validating input and state at system boundaries versus deep within business logic, and where each belongs.

4 — Immutability

Explains how immutable objects eliminate mutation after construction, closing off a whole class of concurrency and state-corruption bugs.

5 — Value Objects

Introduces value objects as small, immutable types defined by their attributes rather than identity, and where they should replace bare primitives.