52 Must-Know OOP Interview Questions and Answers 2025

OOP Fundamentals

1.
What is Object-Oriented Programming (OOP)?
2.
What is the difference between procedural and Object-Oriented programming?
3.
What is encapsulation?
4.
What is polymorphism? Explain overriding and overloading.
5.
What is inheritance? Name some types of inheritance.
6.
What is an abstraction? Name some abstraction techniques.
7.
What is a class in OOP?
8.
What is an object in OOP?
9.
How do access specifiers work and what are they typically?
10.
Name some ways to overload a method.
11.
What is cohesion in OOP?
12.
What is coupling in OOP?

Class Relationships and Design

13.
What is a constructor and how is it used?
14.
Describe the concept of destructor or finalizer in OOP.
15.
Compare inheritance vs. mixin vs. composition.
16.
Explain the concept of an interface and how it differs from an abstract class.
17.
Can a class have multiple parents in a single-inheritance system?
18.
How would you design a class to prevent it from being subclassed?
19.
Explain the ‘is-a’ vs ‘has-a’ relationship in OOP.
20.
Explain how aggregation relationship is represented in OOP.
21.
What is method overriding, and what rules apply to it?
22.
Describe the use of static methods and when they are appropriate.

Advanced OOP Concepts

23.
What is multiple inheritance and what are some of its disadvantages?
24.
Can you explain the ‘diamond problem’ in multiple inheritance?
25.
How does OOP languages support polymorphism under the hood?
26.
What are generics, and how can they be useful in OOP?
27.
Explain the concept of object composition and its benefits.
28.
What is Liskov Substitution Principle (LSP)? Provide some examples of violation and adherence.
29.
What is the dependency inversion principle?
30.
How can the open/closed principle guide object-oriented design?
31.
Describe how the Interface Segregation Principle affects system design.
32.
What is a mixin, and how does it differ from traditional inheritance?

Practical Use and Patterns

33.
How would you refactor a class that has too many responsibilities?
34.
Describe a singleton pattern and discuss its pros and cons.
35.
What is a factory method, and when should it be used?
36.
Explain the builder pattern and where you might apply it.
37.
What is the pattern, and how does it relate to OOP?
38.
When would you use the Adapter pattern?
39.
Can you explain the use of the Decorator pattern?
40.
Describe the Observer pattern and a scenario in which you might use it.
41.
What are the advantages of using the Command pattern?
42.
How does the Strategy pattern provide flexibility in objects?

OOP Best Practices

43.
What are some common OOP design anti-patterns?
44.
How do you ensure that your objects are properly encapsulated?
45.
Name some techniques for reducing coupling between classes.
46.
How does immutability help in object-oriented design, and how can it be implemented?
47.
What tools or techniques would you use to document an object-oriented design?
48.
How do you address circular dependencies in an OOP system?
49.
Explain how to apply unit testing to object-oriented code.
50.
What strategies can be used to safely refactor legacy object-oriented code?
51.
How can the principles of OOP help in achieving a modular and maintainable codebase?
52.
How do you balance the use of OOP principles with performance considerations in a system design?

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52 OOP interview questions

What is Object-Oriented Programming (OOP)?

What is the difference between procedural and Object-Oriented programming?

What is encapsulation?

What is polymorphism? Explain overriding and overloading.

What is inheritance? Name some types of inheritance.

What is an abstraction? Name some abstraction techniques.

What is a class in OOP?

What is an object in OOP?

How do access specifiers work and what are they typically?

Name some ways to overload a method.

What is cohesion in OOP?

What is coupling in OOP?

What is a constructor and how is it used?

Describe the concept of destructor or finalizer in OOP.

Compare inheritance vs. mixin vs. composition.

Explain the concept of an interface and how it differs from an abstract class.

Can a class have multiple parents in a single-inheritance system?

How would you design a class to prevent it from being subclassed?

Explain the ‘is-a’ vs ‘has-a’ relationship in OOP.

Explain how aggregation relationship is represented in OOP.

What is method overriding, and what rules apply to it?

Describe the use of static methods and when they are appropriate.

What is multiple inheritance and what are some of its disadvantages?

Can you explain the ‘diamond problem’ in multiple inheritance?

How does OOP languages support polymorphism under the hood?

What are generics, and how can they be useful in OOP?

Explain the concept of object composition and its benefits.

What is Liskov Substitution Principle (LSP)? Provide some examples of violation and adherence.

What is the dependency inversion principle?

How can the open/closed principle guide object-oriented design?

Describe how the Interface Segregation Principle affects system design.

What is a mixin, and how does it differ from traditional inheritance?

How would you refactor a class that has too many responsibilities?

Describe a singleton pattern and discuss its pros and cons.

What is a factory method, and when should it be used?

Explain the builder pattern and where you might apply it.

What is the pattern, and how does it relate to OOP?

When would you use the Adapter pattern?

Can you explain the use of the Decorator pattern?

Describe the Observer pattern and a scenario in which you might use it.

What are the advantages of using the Command pattern?

How does the Strategy pattern provide flexibility in objects?

What are some common OOP design anti-patterns?

How do you ensure that your objects are properly encapsulated?

Name some techniques for reducing coupling between classes.

How does immutability help in object-oriented design, and how can it be implemented?

What tools or techniques would you use to document an object-oriented design?

How do you address circular dependencies in an OOP system?

Explain how to apply unit testing to object-oriented code.

What strategies can be used to safely refactor legacy object-oriented code?

How can the principles of OOP help in achieving a modular and maintainable codebase?

How do you balance the use of OOP principles with performance considerations in a system design?

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