Beginner~3h
OOP Design Principles in Low-Level DesignInterview Readiness Check
The named principles beyond SOLID — DRY, KISS, YAGNI, Tell Don't Ask, CQS, Composition over Inheritance, Program to Interfaces — and exactly when violating each one is justified.
DRYKISSYAGNITell Don't AskCQScommand query separationcomposition over inheritanceprogram to interfacesfail fastdefensive programmingprinciple of least surprise
Learning path
What this module tests
- Conceptual understanding of oop design principles fundamentals
- Trade-offs and design decisions in real system scenarios
- DRY and KISS — applied knowledge
- Interview-style reasoning and explanation quality
Free to start
Take the OOP Design Principles check →
10 questions · Dimension scoring · AI coach feedback · Shareable result
Test your knowledge — free →No credit card · Takes 10–15 min
Frequently asked questions
- What does the OOP Design Principles check test?
- The check covers the named principles beyond solid — dry, kiss, yagni, tell don't ask, cqs, composition over inheritance, program to interfaces — and exactly when violating each one is justified. Questions span beginner to advanced difficulty and test both conceptual understanding and practical trade-off reasoning.
- What keywords should I know for OOP Design Principles?
- Key concepts include: DRY, KISS, YAGNI, Tell Don't Ask, CQS, command query separation, composition over inheritance, program to interfaces, fail fast, defensive programming, principle of least surprise. These frequently appear in low-level design interviews at product and infrastructure companies.
- How many questions are in the check?
- Each check has 10 questions — a mix of MCQ and short-answer. You get scored by dimension (e.g., scalability, consistency) so you know exactly where to focus.
- How long does it take to study OOP Design Principles?
- Most engineers spend around 3 hours on this module. The check itself takes about 10–15 minutes. You can retake it up to 3 times per day.
- What prerequisite knowledge do I need before OOP Design Principles?
- OOP Design Principles builds on OOP Fundamentals. Complete those first for the best results.
- Is DRY, KISS, YAGNI covered?
- Yes. The OOP Design Principles module covers DRY, KISS, YAGNI among other key concepts. The check includes questions that reflect real low-level design interview patterns.