Beginner-Level OOPS Interview Questions (With Simple Answers)

⭐ Introduction

Object-Oriented Programming (OOPS) is one of the most important topics in software development interviews.
At the beginner level, interviewers mainly test your conceptual understanding, not complex coding.

This article covers frequently asked beginner-level OOPS interview questions with simple, clear answers.

🔹 1. What is OOPS?

OOPS (Object-Oriented Programming System) is a programming approach that uses objects and classes to design software.

It focuses on:

• Data
• Behavior
• Real-world modeling

👉 Example languages: C#, Java, C++, Python

🔹 2. What are the four pillars of OOPS?

The four pillars of OOPS are:

1️⃣ Encapsulation – Data hiding
2️⃣ Abstraction – Hiding implementation details
3️⃣ Inheritance – Reusing code
4️⃣ Polymorphism – One method, many forms

🔹 3. What is a Class?

A class is a blueprint or template used to create objects.

It defines:

• Variables (fields)
• Methods (functions)

👉 Example:
Car is a class.

🔹 4. What is an Object?

An object is a real instance of a class.

👉 If Car is a class,
then myCar is an object of the Car class.

🔹 5. Difference between Class and Object

🔹 6. What is Encapsulation?

Encapsulation means wrapping data and methods together and restricting direct access to data.

👉 Achieved using:

• private fields
• public properties

🔹 7. What is Abstraction?

Abstraction means showing only essential details and hiding complex implementation.

👉 Example:
You use a TV remote, but don’t know how signals work internally.

🔹 8. What is Inheritance?

Inheritance allows a child class to acquire properties and methods of a parent class.

👉 Example:

Animal → Dog

Dog inherits properties of Animal.

🔹 9. What is Polymorphism?

Polymorphism means one method, many forms.

👉 Example:

• MakeSound()
• Dog → Bark
• Cat → Meow

🔹 10. What is Method Overloading?

Method overloading means:

• Same method name
• Different parameters
• Happens in the same class

👉 Example:

Add(int a, int b)
Add(double a, double b)

🔹 11. What is Method Overriding?

Method overriding means:

• Same method name
• Same parameters
• Different implementation in child class

👉 Uses:

• virtual
• override

🔹 12. What is a Constructor?

A constructor is a special method that:

• Has same name as class
• Runs automatically when object is created
• Initializes object data

🔹 13. Types of Constructors in C#

1️⃣ Default constructor
2️⃣ Parameterized constructor
3️⃣ Static constructor

🔹 14. What is the this keyword?

this refers to the current object of the class.

👉 Used to:

• Distinguish fields and parameters
• Call another constructor

🔹 15. What is the base keyword?

base refers to the parent class object.

👉 Used to:

• Call parent constructor
• Call parent methods

🔹 16. What are Access Modifiers?

Access modifiers control visibility of members.

Common access modifiers:

• public
• private
• protected
• internal

🔹 17. Difference between public and private

🔹 18. What is a Property in C#?

A property provides controlled access to private fields using:

• get
• set

It supports validation and encapsulation.

🔹 19. What is a Static Member?

A static member:

• Belongs to the class
• Shared among all objects
• Accessed using class name

🔹 20. Difference between Static and Instance Members

🔹 21. What is an Interface?

An interface is a contract that contains only method declarations.

Classes that implement it must define all methods.

🔹 22. Difference between Abstract Class and Interface

🔹 23. What is a Sealed Class?

A sealed class cannot be inherited.

👉 Used to prevent further extension.

🔹 24. Can C# support multiple inheritance?

❌ No (using classes)
✔ Yes (using interfaces)

🔹 25. Why is OOPS important?

OOPS helps in:
✔ Code reusability
✔ Maintainability
✔ Scalability
✔ Security
✔ Real-world modeling

📝 Quick Tip for Interviews

👉 Always explain OOPS concepts with:

• Definition
• Real-world example
• Small code example (if asked)

🎉 Conclusion

These beginner-level OOPS interview questions cover 90% of basic interview expectations.
A strong grip on these concepts builds confidence and prepares you for advanced OOPS questions.