Low Level Design
LLD interview prep — patterns, OOP, and real designs
Twelve modules from interview framework to architect-level patterns. One CampusOS platform grows with every chapter — parking, booking, caching, and games all plug into the same design vocabulary.
LLD vs HLD: What Interviewers Actually Test
Where low-level design stops and high-level design starts — and why both matter in the same interview loop.
The Six-Step Whiteboard Framework
A repeatable flow from vague prompt to working class diagram and core Java skeleton.
Functional vs Non-Functional Requirements
The questions that prevent you from designing the wrong system in the first five minutes.
Top LLD Interview Mistakes
The patterns that fail candidates even when they know SOLID — and how to avoid them.
Four OOP Pillars Applied to Design
How encapsulation, abstraction, inheritance, and polymorphism show up in real class diagrams.
Composition Over Inheritance
When to compose collaborators and when a subtype is the right model.
Finding Nouns, Verbs, and Ownership
Turn a problem statement into entities before you name a single method.
Encapsulation and Invariants
Protect state with contracts so invalid objects never exist.
SOLID as Diagnostic Questions
Five questions to ask about every class — with interview framing, not textbook definitions.