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Top 51 OOP Concepts Interview Questions & Answers (2026)

51 Questions 28 Beginner 15 Intermediate 8 Advanced

About OOP Concepts

Top 100 Object-Oriented Programming interview questions covering encapsulation, inheritance, polymorphism, abstraction, SOLID principles, design patterns, and best practices. Companies hiring for OOP Concepts roles test this knowledge at every stage — from first-round screens that check the basics to final-round conversations about real-world trade-offs.

What to Expect in a OOP Concepts Interview

Expect a mix of conceptual and practical OOP Concepts questions: clear definitions and core-concept checks for junior roles, hands-on scenario questions for mid-level roles, and architecture or trade-off discussions for senior roles. Interviewers usually move from foundational topics toward the kind of problems you'd actually face on the job.

How to Use This Guide

Work through the OOP Concepts questions in order — Beginner, then Intermediate, then Advanced — so each concept builds on the last. Every question has its own page; bookmark the ones that trip you up and revisit them the day before your interview.

Curated by Tech Baithak Editorial Team · Last updated: May 2026

Beginner 28 questions

Core concepts every OOP Concepts developer must know.

01 What is Object-Oriented Programming (OOP)? 02 What is a class? 03 What is an object? 04 What is encapsulation? 05 What is abstraction in OOP? 06 What is inheritance in OOP? 07 What is polymorphism? 08 What is the difference between overloading and overriding? 09 What is a constructor? 10 What is the difference between an interface and an abstract class? 11 What is the "this" keyword? 12 What is the difference between composition and inheritance? 13 What is method overriding? 14 What are access modifiers? 15 What is a static method and a static variable? 16 What is the difference between stack and heap memory in OOP? 17 What is the difference between == and .equals() in Java? 18 What is a final keyword in Java? 19 What is object cloning? 20 What is toString() and why override it? 21 What is type casting in OOP? 22 What is method hiding vs method overriding? 23 What is cohesion and coupling in OOP? 24 What are design patterns in OOP? 25 What is the Singleton pattern? 26 What is the Factory pattern? 27 What is method chaining? 28 What is the Iterator pattern?

Intermediate 15 questions

Practical knowledge for developers with hands-on experience.

01 What are the SOLID principles? 02 What is the Observer pattern? 03 What is the Strategy pattern? 04 What is the Decorator pattern? 05 What is the Builder pattern? 06 What is the Adapter pattern? 07 What is the Template Method pattern? 08 What is the Command pattern? 09 What is the Facade pattern? 10 What is the Proxy pattern? 11 What is a mixin? 12 What is dependency inversion principle (DIP)? 13 What is the difference between early and late binding? 14 What is the Open/Closed Principle? 15 What is the Liskov Substitution Principle?

Advanced 8 questions

Deep expertise questions for senior and lead roles.

01 What is the Interface Segregation Principle? 02 What are GRASP principles? 03 What is cohesion vs coupling trade-offs in practice? 04 What is the Composite pattern? 05 What is the Chain of Responsibility pattern? 06 What is the State pattern? 07 What is meta-programming and reflection in OOP? 08 What are immutable objects and why are they important?

Back to All Topics 51 questions total