Top 25 OOP Interview Questions and Answers in 2024

Editorial Team

Top 25 OOP Interview Questions And Answers

What is OOP? Object-Oriented Programming is a model that organizes software design around data, or objects, rather than functions and logic.

Below are the Top 25 OOP Interview Questions And Answers. Also, there are samples to guide you on how you are supposed to respond to each question.

1. Why Are You Interested In This Role?

“To start with, I am a big fan of all computer activities and I spend most of my time with computers. I must say that I want to be part of the team that is helping your company get the best information technology programs that will aid your company to achieve its goals. And, I am a person who likes learning from others as well. I want to improve my skills too by learning and improving my skills too. I will be happy to offer my skills to you and learn from you as well. In fact, success comes from finding win-win solutions!”

2. What Are The Roles Of OOP?

“The crucial function of OOP is that it is used to structure a software program into simple, reusable pieces of code blueprints (usually called classes), which are used to create individual instances of objects.”

3. What Are The Qualities That A Programmer Needs To Be Successful?

 “First and foremost, being patient is key for the OOP experts. The patient is the most important trait to become a great OOP programmer. Secondly, a good OOP programmer should have a high degree of creativity and problem solving since there is a lot that needs to be done in a creative way and a lot of issues that need to be solved intelligently. Lastly, an OOP programmer should be a logical thinker and self-disciplined at all times.”

4. What Major Challenges Did You Have In Your Previous Role, And How Did You Manage Them?

“As an OOP programmer, things might not go as planned for the day. Especially when it comes to the users,  they may have opinions about how a product should work. These opinions may differ from those of your development team. But it’s often difficult for new programmers to understand what their users want since they rarely get to interact with them directly. This is a challenge that is facing most of the computer programmers in this industry.”

5. Describe Your Daily Routine As An OOP Programmer?

“After setting my foot to my office, I would start the day by checking my mails and see what new we have for the day. After that, I would check my Jira and pick a few issues to sort and fix. I would attend to my client’s queries and solve problems or fix issues with their software. I would then meet new clients to explain what exactly they want and start working on new projects right away. I would then follow up on previous projects to see their progress. That would be a very busy day at work.”

6. Describe Briefly About Your Experience

“After gaining a Diploma certificate in Computer Science, I was recruited as an intern in a video production company where I got a very big exposure in this career. After working as an intern for a year, I went back to school and earned a degree in the same course. I was permanently employed in the company I worked for as an intern again. This time, I was the assistant OOP programmer. I would help the OOP programmer with some duties and take over when he was not in. I worked as an assistant programmer for two years. That gives me a score of three working experiences in this field. I hope I will get a chance to use my experience to better your company.”

7. What Are The Main Features Of Oops?

What are the Five Main Features of OOPs?

  • Classes.
  • Objects.
  • Inheritance.
  • Polymorphism.
  • Data Abstraction and Encapsulation.

8. What Are The Important Reasons For Using Interfaces?

  • Interfaces are used to achieve abstraction.
  • Designed to support dynamic method resolution at run time
  • It helps you to achieve loose coupling.
  • Allows you to separate the definition of a method from the inheritance hierarchy

9. What Are Important Reasons For Using Abstract Class?

  • Abstract classes offer default functionality for the subclasses.
  • Provides a template for future specific classes
  • Helps you to define a common interface for its subclasses
  • Abstract class allows code reusability.

10. What Is The Difference Between Abstract Class And Interface?

  • Type of methods – Interface can have only abstract methods. An abstract class can have abstract and non-abstract methods. From Java 8, it can have default and static methods also.
  • Final Variables – Variables declared in a Java interface are by default final. An abstract class may contain non-final variables.
  • Type of variables – Abstractclass can have final, non-final, static and non-static variables. The interface has only static and final variables.
  • Implementation – Abstract class can provide the implementation of the interface. Interface can’t provide the implementation of an abstract class.
  • Inheritance vs Abstraction – A Java interface can be implemented using the keyword “implements” and an abstract class can be extended using the keyword “extends”.
  • Multiple implementations – Ann interface can extend another Java interface only, an abstract class can extend another Java class and implement multiple Java interfaces.
  • Accessibility of Data Members – Members of a Java interface are public by default. A Java abstract class can have class members like private, protected, etc.”

11. What Is A Garbage Collection, And How Does It Work?

“In Java, garbage collection is the process of managing memory, automatically. It finds the unused objects (that are no longer used by the program) and deletes or removes them to free up the memory. The garbage collection mechanism uses several GC algorithms. The most popular algorithm that is used is Mark and Sweep.”

12. Name The Types Of Garbage Collection In Java

“There are four types of the garbage collector in Java that can be used according to the requirement:

  • Serial Garbage Collector.
  • Parallel Garbage Collector.
  • Concurrent Mark Sweep (CMS) Garbage Collector.
  • Garbage First (G1) Garbage Collector.


13. What Are The Top Benefits Of Using OOP?

  • OOP models complex things as reproducible, simple structures
  • Reusable, OOP objects can be used across programs
  • Allows for class-specific behavior through polymorphism
  • Easier to debug, classes often contain all applicable information to them
  • Secure, protect information through encapsulation

14. Take Us Through On How You Would Organize Your OOP

·         I would start by creating a parent class for all dogs as a blueprint of information and behaviors (methods) that all dogs will have, regardless of type.

·         Then create child classes to represent different subcategories of dogs under the generic parent blueprint.

·         Then add unique attributes and behaviors to the child classes to represent differences

·         And lastly create objects from the child class that represent dogs within that subgroup

15. Take Us Through The Four Principles Of OOP

The four pillars of object-oriented programming are:

  • Inheritance –child classes inherit data and behaviors from the parent class
  • Encapsulation –containing information in an object, exposing only selected information
  • Abstraction –only exposing high-level public methods for accessing an object
  • Polymorphism – many methods can do the same task

16. What Are The Benefits Of Encapsulation?

The benefits of encapsulation are summarized here:

·         Adds security: Only public methods and attributes are accessible from the outside

·         Protects against common mistakes: Only public fields & methods are accessible, so developers don’t accidentally change something dangerous

·         Protects IP: Code is hidden in a class, only public methods are accessible by the outside developers

·         Supportable: Most code undergoes updates and improvements

·         Hides complexity: No one can see what’s behind the object’s curtain!

17. Briefly Talk About Method Overloading

When a class has multiple methods with the same names but a different set of parameters, it is called Method overloading. You can proceed with method overloading, only if your methods satisfy any one of the following rules;

·         Has different parameters

·         Has different return types

·         Has different access modifiers 

18. What Are Some Tenets Of Object-Oriented Programming?

·         Objects comprise data that define its state and methods that define its behavior. Each object encapsulates these two entities.

·         The internal implementation of object methods is invisible to the user. This way objects abstract state changes under a simplified external API.

·         Objects are instances of classes. Classes are blueprints to build objects. The class of an object is also its type.

·         Classes can inherit both state and behavior from other classes. Based on this notion, objects of the subclass support casting into objects of the parent class.

·         This form of casting gives rise to polymorphism. The program can implicitly cast an object of a class to an object of the class’s ancestors.

19. What Is The Difference Between Class And An Object?

·         Object is an instance of a class. Class is a blueprint or template from which objects are created.

·         Object is a real-world entity like pens, laptop, mobile, keyboard, mouse, table, chair, etc while class is a group of similar objects

·         Object is a physical entity while class is a logical entity.

·         Object is created many times as per requirement while class is declared once.

·         In object there are many ways to create an object in java such as new keyword, newInstance() method, clone() method, factory method, and deserialization while in class there is only one way to define the class in java using the class keyword.

20. Why Did You Quit Your Previous Role In The Company That You Were Working For?

“I loved working for my previous employer, but they had employed me on a contract. After the contract, I felt that it was not good for me to renew the contract. I mean, it is always good to work in different environments. I also wanted to play a role as a top programmer since, in my previous role, I was an assistant.”

21. Tell Us Your Biggest Strength

“As a programmer, I like working in teams. Talent wins games, but teamwork and intelligence win championships. As a programmer, you may have spent the whole on computers, and still, other duties are awaiting you at the same time. It is good to have a team that can help you manage all your projects. Having a team of smart people leads to quality work. I would say that I work best in teams. That’s my strength.”

22. How Would You Build A Strong Team To Work With In Your Department?

“To have a great team to work with I would;

·         Start by setting my expectations of what is required to evaluate their capabilities

·         Hold performance reviews to pick the best

·         Maintain regular communication with all the employees to learn more about them through one on one engagement.”

23What Is Your Biggest Fear In Your Career

“The biggest fear in my career would be having a team that will lead to poor results. I would consider this as a total failure and no one would want that. I am always focused on working with people who can bring productivity to their company. That would be my biggest fear in my career.”

24. What Kind Of Environment Do You Like Working In?

“As far as the nature of this job is concerned, I have spent so much time working in a super busy environment. I have adapted to this kind of environment, and now it’s my best. I would still be interested in working in a busy environment as before because it brings motivation and morale among the employees working together. No one would love to work in an environment where other employees are idling around while you are busy doing your job. It is better to work in an environment where you see everyone else around you is as busy as you are.

25. What Do You Think Are The Major Challenges You Are Likely To Face As An OOP Programmer In Our Company?

·         Not understanding users – Talk direct to the people dealing with the users, and test your products

·         Debugging – reproduce the errors and seek help

·         Time estimation challenges – Break down tasks and time yourself well

·         Coping up with technology – Take some time to understand new projects, and keep up with the latest trends

·         Security threats – Keep your work station secure and use parameterized queries for SQL injections


OOP programming is a challenging career but you must show your interviewer that you are capable of working them out as soon as you can. Answer the questions with confidence, straight to the point, and you will pass the interview. All the best.