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Top 51 OOP Concepts Interview Questions & Answers (2026)
51 Questions
28 Beginner
15 Intermediate
8 Advanced
About OOP Concepts
This technology is widely used in software development and is a frequent topic in technical interviews at companies of all sizes.
What to Expect in a OOP Concepts Interview
Interviews cover both foundational concepts and practical application of this technology, with questions ranging from definitions to architectural decision-making.
How to Use This Guide
Work through questions in order of difficulty to build your understanding progressively. Bookmark challenging questions and revisit them 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?
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51 questions total