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Top 14 OOPs Interview Questions and Answers

18/Sep/2021 | 10 minutes to read


Here is a List of essential OOPs Interview Questions and Answers for Freshers and mid level of Experienced Professionals. All answers for these OOPs questions are explained in a simple and easiest way. These basic, advanced and latest OOPs questions will help you to clear your next Job interview.

OOPs Interview Questions and Answers

These interview questions are targeted for OOPs Object Oriented Programming system. You must know the answers of these frequently asked OOPS interview questions to clear a developer interview. These questions are common for any object oriented programming language like Java, C#, PHP, Python etc.

1. What is the concept of OOPs?

OOPs or Object Oriented Programming systems have a certain set of principles or concepts to write good programming logic. Basic OOPs concepts include:

  • Abstraction
  • Encapsulation
  • Inheritance
  • Polymorphism

2. What is class, object and method?

Object Oriented programming systems organize or manage the code by creating types in the form of classes. A Class contains the code that represents a specific entity and defines what an entity can do. For example, A BankAccount entity can be organized by a class 'BankAccount'.
An entity has certain behavior, The code implements this behavior in the form of operations or functions using Methods and Properties.
An Object is a block of memory that has been configured and allocated according to the entity - which exists in the form of class.

3. What do you understand from object oriented analysis, design and programming?

When you see the word 'object-oriented', there are other terms such as object-oriented programming, object-oriented design and object-oriented analysis. All these three terms are inter-related as to understand the problem, design the solution and build it or in simple terms analysis, design and programming.

  • Object-Oriented Analysis explains about the problem you are trying to solve and gives the answers of questions about the problem.
  • Object-Oriented Design mainly focuses on the strategy, how are you going to implement it?
  • Object-Oriented Programming is the implementation of a solution based on design.

4. What is Abstraction?

Abstraction models the relevant attributes and interaction of an entity in the form of classes to define an Abstract representation of a system. For example, A BankAccount class can provide the abstraction for bank account concept- means It can include all relevant attributes and interaction to create a bank account and Now you can define classes to create any type of bank account like SavingBankAccount which inherits from BankAccount class.

5. Explain Encapsulation.

Encapsulation allows to hide internal state and functionality of objects. It allows access through a public set of properties or functions. Encapsulation provides the ability for a class to specify how accessible each of its members to the code outside of this class. Members of the class which are not intended to be used outside of this class can be hidden to limit potential for coding errors. For example, the BankAccount class may contain many private things.

6. Explain Inheritance in detail.

Inheritance provides the ability to create new abstractions based on existing abstraction. Inheritance is one of the primary concepts of object oriented programming. It allows you to create new classes that modify, extend and reuse the behavior defined in other classes. The class whose members are reused, modified or extended is called base class and the class which inherits those members is called child class. For example, the SavingAccount class can inherit the members from the BankAccount base class. Inheritance is referred to as a 'is a relationship'.

7. Explain Polymorphism.

Polymorphism allows you to implement different inherited properties or methods in different ways across abstractions.
For example, you have different abstractions like SavingAccount, CurrentAccount etc which are inherited from base class 'BankAccount' and these abstractions implement different tasks at the end of month. Now you can override the base class method 'MonthEndTasks' to create specific behavior in these different abstractions. If you are familiar with C# you can visit OOPs Concept to see examples.

8. What is Aggregation?

The concept of Aggregation is a type of another relationship in which one object is composed of other objects but the lifetimes of objects not tied to each other. So Aggregation is referred to as a 'has a relationship' between objects but it does not imply ownership. For example, A Department has many employees so we can say Department Object has collection of employee objects and lifetime of employees not tied to each other or the existence of department. If we remove employee, the department can continue to exist and If we end the department the individual employee can continue to exist and do their own thing.

9. What is composition?

Composition is a more specific form of Aggregation. It is based on a 'has a relationship' between objects but it implies ownership. For example, A car has an engine or it owns an engine. Composition implies ownership so an engine has no purpose without a car. In composition, if the owning object is destroyed the contained objects are destroyed too. So in Programming if you are defining a owning class, you may need to write constructor and destructor methods to take care of creating and deleting internal objects.

10. What is Association?

Association is referred to as a structural relationship between the classes of objects where one object instance causes another to perform some operation on its behalf. Association does not represent the behavior rather than It allows to associate one type of objects with another type of objects. Association relationships can be one-to-one, one-to-many, many-to-one and many-to-many. For example, A Role can belong to one or many users and One User may have one or more than one role.

11. What is Delegation?

Delegation allows the objects to perform some operations or actions beyond the scope of the object. For example, Some Parents are working professionals, so they hire a baby caretaker. But what will happen if the baby gets sick? There is a note on the table "In case of emergency, please call XYZ on 999-999-999". So XYZ is the delegate here.
            //parent class
            babyCareTaker.delegate = XYZ
            [babyCareTaker lookAfter:baby]

            //babyCareTaker class
            if (baby.isSick)
            [delegate callAbout:baby]
Every object-oriented programming supports the concept delegates. For more visit Delegation.

12. What is Cohesion?

Cohesion is the degree of measure that tells how well-focused a class is designed. A class designed with a single business responsibility ensures high cohesion and It should implement the methods which are intended for a well focused purpose. A benefit of high cohesion is that classes are easier to maintain and provide better readability and reusability.

13. What is Coupling?

Coupling is a degree of measure that indicates how closely connected two classes are. If the coupling is high then changes in one class affects the code in other classes and makes code difficult to maintain and change. Applications with low coupling ensure better code maintainability and any code changes can be easily implemented without affecting other classes or systems. A good application design must have High Cohesion and Low Coupling.

14. What is the function of a user diagram or use case diagram?

Use Case Diagram defines the possible interactions of a user with the system. It encapsulates the system behavior, use cases and different actors of the system. Use-case diagrams are useful during the analysis and design phase to identify the required classes and tests for the system. Use-case diagram shows how the actors use the system rather than how the system works internally. For more visit Use-case diagrams.

15. What is the role of constructor and destructor in any object-oriented programming language?

Some General Interview Questions for OOPs

1. How much will you rate yourself in OOPs?

When you attend an interview, Interviewer may ask you to rate yourself in a specific Technology like OOPs, So It's depend on your knowledge and work experience in OOPs.

2. What challenges did you face while working on OOPs?

This question may be specific to your technology and completely depends on your past work experience. So you need to just explain the challenges you faced related to OOPs in your Project.

3. What was your role in the last Project related to OOPs?

It's based on your role and responsibilities assigned to you and what functionality you implemented using OOPs in your project. This question is generally asked in every interview.

4. How much experience do you have in OOPs?

Here you can tell about your overall work experience on OOPs.

5. Have you done any OOPs Certification or Training?

It depends on the candidate whether you have done any OOPs training or certification. Certifications or training are not essential but good to have.


We have covered some frequently asked OOPs Interview Questions and Answers to help you for your Interview. All these Essential OOPs Interview Questions are targeted for mid level of experienced Professionals and freshers.
While attending any OOPs Interview if you face any difficulty to answer any question please write to us at Our IT Expert team will find the best answer and will update on the portal. In case we find any new OOPs questions, we will update the same here.