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Most Important OOPs Interview Questions

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OOP (Object-Oriented Programming) is a popular programming model that is based on the idea of Objects and Classes. You can think of objects as real-world instances of entities such as classes, each with its own set of characteristics and behaviors. Recruiters at big tech companies look for candidates who have expertise in OOPs as these models are widely used across many programming languages such as C++, C#, Java, Python, etc.

Recruiters ask OOPs interview questions about OOP features like inheritance, polymorphism, encapsulation, and data abstraction. OOPs interview questions can also be asked on the programming language you choose.

Thorough knowledge of Object-Oriented programming is essential for solving problems based on core data structures and algorithms. Given that your problem-solving abilities are intensely evaluated in FAANG+ interviews, practicing OOPs interview questions focused on core concepts can help you stand out.

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In this article, we’ll look at some popular OOPs interview questions and answers that you can expect at technical interviews.

Here’s what we’ll discuss in this article:

  • Top 20 OOPs Interview Questions and Answers
  • FAQs on OOPs Interview Questions

Top 20 OOPs Interview Questions and Answers

This section will look at the most commonly asked OOPs interview questions at technical interviews, along with answers.

Q1. Why are OOPs actively used in today’s world?

The OOP model is actively used for several reasons. The main reasons include:

  • The model has proven extremely useful in building large-scale software applications and programs, especially those used in manufacturing, banking, and telecommunication.  
  • The model makes it easy to manage and modify code at various stages of the software production process.
  • OOPs have the feature of data hiding, allowing developers to secure data and information better.

Q2. Which are the major Object-Oriented Programming Languages?

The most popular OOP languages are:

  • Python
  • Java
  • C#
  • Ruby
  • Perl
  • Scala

Q3. What do you understand about a programming paradigm? What are the fundamental types of programming paradigms that are used?

Programming paradigms are a method to classify programming languages based on their core features. The two main programming paradigms include:

  • Imperative Programming Paradigm
  • Declarative Programming Paradigm

OOPs is a type of Imperative Programming Paradigm.

Q4. What are the main features of Object-Oriented Programming?

The main features of OOPs include:

  • Inheritance
  • Encapsulation
  • Data Abstraction
  • Polymorphism

Q5. What do you understand about an Object in OOPs?

This is a popular OOPs interview question asked at tech interviews. An Object is a basic entity in the OOP model and can take any definition. An object, based on its definition, can assume different states or behaviors.

Q6. What do you understand about a Class in OOPs?

A class is a collection of objects of different states/behaviors. Classes define the nature of an Object and future Objects and are the logical entities of an OOP model.

Q7. Explain the fundamental difference between a Class and a Structure.

This again is one of the more popular OOPs Interview Questions asked at tech interviews at FAANG and Tier-1 companies.

A class is essentially a collection of objects and contains instructions on the different actions on the Objects.

On the other hand, a structure contains a list of variables that can be of different data types to be used in the designing of a software model.

Q8. What are the building blocks of the Object-Oriented Programming Model?

The fundamental building blocks of the OOP model are:

  • Classes
  • Objects
  • Methods
  • Attributes

Q9. What is a Method in the OOP model?

Methods are essential functions inside a class and define the behavior of the Objects in a class. Methods are one of the fundamental building blocks of the Object-Oriented Programming Model.

Q10. What do you understand by Encapsulation in OOP?

Encapsulation is a primary feature of the OOP model and is a method that is used to capture all the required data and information in a capsule to hand out to the user. Only the required details are visible to the user, and all other details that aren’t relevant to the user are hidden through Encapsulation.

Q11. What do you understand by Polymorphism in OOP?

This is a popular Java OOPs interview question asked at technical interviews. Polymorphism is a process by which a given object, method, or code snippet is made to behave differently under different circumstances.

Q12. What are the two types of polymorphism in the OOP model?

The two types of Polymorphism are - Compile Time Polymorphism and Runtime Polymorphism.

Compile Time Polymorphism: The process of Polymorphism, when it occurs during compile time, is known as Compile Time Polymorphism. This essentially means that the compiler decides what value or shape an Object takes in a program.

Runtime Polymorphism: When Polymorphism occurs at Runtime, the process is known as Runtime Polymorphism.

Q13. What is Inheritance in OOP?

Inheritance is a feature in the OOP model that allows a Class to inherit the characteristics of another Class or a group of Classes.

Q14. What are the different types of Inheritance in OOP?

The different types of Inheritance in OOP are:

  • Single Inheritance
  • Multiple Inheritance
  • Multilevel Inheritance
  • Hierarchical Inheritance
  • Hybrid Inheritance

Q15. What is Abstraction in OOPs? What are the two methods by which data Abstraction can be achieved?

Abstraction is a fundamental feature of OOP in which the implementation details are hidden, and only the necessary details are displayed. Abstraction can be achieved in two main ways:

Abstract Class and Abstract Method.

Q16. What is the fundamental difference between Multiple and Multilevel Inheritance in OOP?

In Multiple Inheritance, a class can inherit the characteristics or features of one or more base classes.

In Multilevel Inheritance, a class inherits the characteristics of another class, which in itself is a subclass of a given base class.

Q17. What do you understand about Hybrid Inheritance?

Hybrid Inheritance is essentially a combination of Multiple and Multilevel Inheritance. In this form of inheritance, a class can display characteristics of multiple inheritance or Multilevel inheritance, or both.

Q18. What are some limitations of the Inheritance feature of the OOP model?

Some limitations of Inheritance include:

  • There’s a lot of jumping back and forth between classes in Inheritance. This increases the time required to execute the program. 
  • If the program needs to be modified, both the Parent and Child classes need to be modified.
  • The parent and child classes get coupled tightly and do not exhibit independent characteristics.

Q19. What are Superclasses and Subclasses in OOP?

A Superclass is a base class that lends characteristics and behaves as a Parent to other Classes. A Subclass is a type of class that inherits the attributes of another class.

Q20. What are Constructors and Destructors?

Constructors and Destructors are special Methods in OOP. A Constructor initializes an Object and also provides memory space for the Object.

A Destructor is when an Object is destroyed and clears the memory and other resources associated with an Object.

We hope this article on top OOPs interview questions will help prepare for coding interviews at tech companies. Practice such questions as much as possible to nail your technical interview.

FAQs on OOPs Interview Questions

Q1. What are some important OOP concepts asked in tech interviews at FAANG+ companies?

The important concepts in OOP that feature in technical interviews at FAANG+ companies include - Encapsulation, Polymorphism, Inheritance, Methods, Objects, and Data Abstraction. 

Q2. Will OOPs interview questions involve writing code in technical interviews?

Yes, you would have to write error-free code to explain certain concepts in OOP during technical interviews. As such, coding up algorithms in technical interviews requires a stronghold in OOPs concepts.

Q3. What are some advantages of using the Object-Oriented Programming Model?

The biggest advantage of using the OOP model is that it enables developers to design large-scale software programs. It is also loaded with many potent features that allow developers to create and design a wide range of software programs and applications.

Q4. Can OOPs Interview Questions in tech interviews be language-based?

Yes, in tech interviews at FAANG+ companies, you can be asked OOPs concepts interview questions, Java OOPs interview questions, Python OOPs interview questions, and C++ OOPs interview questions.

Q5. Are OOPs concepts important to solve problems in Data Structures and Algorithms?

Yes, having a solid grasp of OOPs concepts is key to solving tricky data structures and algorithms problems. Your extent of knowledge in OOPs also defines how good of a problem-solver you are, and problem-solving is the primary skill that is tested in tech interviews at FAANG+ companies.

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