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OOPs Interview Questions With Answers And Resources

list of top OOPs Interview questions with their answers and resources

Greetings! I am Nasyx Rakeeb, a professional MERN stack developer with 5+ years of experience in programming. And today in this article I will share a list of top OOPs Interview questions with their answers and resources. So without wasting further time let’s dive in.

OOPs Interview Questions And Answers

1. What is Object Oriented Programming

In this paragraph, we are going to learn what is Object Oriented Programming in simpler terms.

Object-Oriented Programming (OOPs) is a type of programming that is based on objects rather than just functions and producers. Moreover, in OOPs individual objects are grouped into classes and these classes have properties and methods. In other words, OOPs implements real-world entities like inheritance, polymorphism, hiding, etc into programming. It also allows binding data and code together.

2. Why use OOPs

OOPs, allow clarity in programming, therefore, allowing simplicity in solving complex problems.

  • Firstly, code can be reused through inheritance thereby reducing redundancy.
  • Also, Data and code are bound together by encapsulation.
  • Seconldy, OOPs allows data hiding therefore private data is kept confidential.
  • Thirdly, problems can be divided into different parts making it simple to solve.
  • Above all, the concept of polymorphism gives flexibility to the program by allowing the entities to have multiple forms.

Also Read: JavaScript Higher Order Functions Explained

3. What are the main features of OOPs

  • Inheritance
  • Encapsulation
  • Polymorphism
  • Data Abstraction

4. What is an object

An object is a real-world entity that is the basic unit of OOPs for example chair, cat, dog, etc. Therefore, different objects have different states or attributes and behaviors.

5. What is a class

A class is a prototype that consists of objects in different states and with different behaviors. In addition to the properties, it has a number of methods that are common to the objects present within that class.

6. What is difference between a class and a structure

User-defined blueprint from which objects are created. It consists of methods or set of instructions that are to be performed on the objectsA structure is basically a user-defined collection of variables that are of different data types

7. What is difference between OOP and SOP

Object-Oriented ProgrammingStructural Programming
Object-Oriented Programming is a type of programming that is based on objects rather than just functions and producersProvides logical structure to a program where programs are divided functions
Bottom-up approachTop-down approach
Provides data hidingDoes not provide data hiding
Can solve problems of any complexityCan solve moderate problems
Code can be reused thereby reducing redundancyDoes not support code reusability

8. Can you call the base class method without creating an instance

Yes, you can call the base class without instantiating it if:

  • It is a static method
  • The base class is inherited by some other subclass

9. What is the difference between a class and an object

A real-world entity which is an instance of a classA class is basically a template or a blueprint within which objects can be created
An object acts like a variable of the classBinds method and data together into a single unit
An object is a physical entityA class is a logical entity
Objects take memory space when they are createdA class does not take memory space when created
Objects can be declared as and when requiredClasses are declared just once

10. What is inheritance

Inheritance is a feature of OOPs which allows classes to inherit common properties from other classes. For example, if there is a class such as a vehicle, other classes like car, bike, etc can inherit common properties from the vehicle class. This property helps you get rid of redundant code thereby reducing the overall size of the code.

Also Read: How To Install And Create Reactjs App On Android

11. What is a superclass

A superclass or base class is a class that acts as a parent to some other class or classes. for example, the vehicle class is a superclass of class cars.

12. What is data abstraction

Data abstraction is a very important feature of OOPs thus allowing displaying only the important information and hiding the implementation details. For example, while riding a bike, you know that if you raise an accelerator the speed will increase but you don’t know how it actually happens. This is data abstraction as the implementation details are hidden from the rider.

13. Differentiate between data abstraction and encapsulation

Data Abstraction Encapsulation
Solves the problem at the design levelSolves the problem at the implementation level
Allows showing important aspects while hiding implementation detailsBinds code and data together into a single unit and hides it from the world

14. What is garbage collection (GC)

GC is an implementation of automatic memory management. In conclusion, the garbage collector frees up space occupied by objects that are no longer in existence.

15. What is the difference between an error and an exception

Errors are problems that should not be encountered by applicationsConditions that an application might try to catch

16. What is polymorphism

Polymorphism refers to the ability to exist in multiple forms. Multiple definitions can be given to a single interface. For example, if you have a class named vehicle, it can have a method named speed but you cannot define it because different vehicles have different speeds. Therefore, this method will be defined in the subclasses with different definitions for different vehicles.

Also Read: Computer Networking Complete Tutorial – Beginner To Advance

17. What is difference between public, private and protected access modifiers

NameAccessibility from own classAccessibility from derived classAccessibility from world

18. What is an exception

An exception is a kind of notification that interrupts the normal execution of a program. In other words, exceptions provide a pattern to the error and transfer the error to the exception handler to resolve it. The state of the program is saved as soon as an exception is raised.

OOPs, programming paradigm is considered a better style of programming. Not only does it help in writing a complex piece of code easily, but it also allows users to handle and maintain them easily as well. Not only that, the main pillar or OOPs – Data abstraction, encapsulation, inheritance, and polymorphism makes it easy for programmers to solve complex scenarios. As a result of these, OOPs is so popular.

20. Name the operators that cannot be overload

  • Scope resolution operator (::)
  • Ternary operator (?:)
  • Member access or Dot operator (.)
  • Pointer to member operator (.*)
  • Size of operator

21. What are tokens

A compiler recognizes a token and it cannot be broken down into component elements. Keywords, identifiers, constants, string literals, and operators are examples of tokens.

Even punctuation characters are also considered tokens. For example brackets, commas, braces, and parentheses.

Also Read: GitHub Repos That You Won’t Believe Exist

22. What is difference between multiple and multilevel inheritance

Multiple InheritanceMultilevel Inheritance
Multiple inheritances come into the picture when a class inherits more than one base class.Multilevel inheritance means a class inherits from another class which itself is a subclass of some other base class.
For example, a class defining a child inherits from two base classes Mother and Father.For example, a class describing a sports car will inherit from a base class Car which inturn inherits another class Vehicle.

23. What is hybrid inheritance

Hybrid inheritance is a combination of multiple and multiple-level inheritance

24. What is hierarchical inheritance

Hierarchical inheritance refers to inheritance where one base class has more than one subclasses. For example, the vehicle class can have a car, bike, etc as its subclasses.

25. What is friend function

A friend function is a friend of class that is allowed to access public, private, or protected data in that same class. If the function is defined outside the class then it cannot access such information.

Firstly, a friend can be declared anywhere in the class declaration. And secondly, it cannot be affected by access control keywords like private, public or protected.

  • Java
  • C++
  • JavaScript
  • Python
  • PHP
  • And many more

26. What are the limitations of OOPs

  • Usually not suitable for small problems
  • Requires intensive testing
  • Takes more time to solve the problem
  • Requires proper planning
  • The programmer should think of solving a problem in terms of objects

27. Differentiate between overloading and overriding

Two or more methods having the same name but different parameters or signatureChild class redefining methods present in the base class with the same parameters/signature
Resolved during compile timeResolved during runtime

Best Resources For OOPs Interview Questions Preparation

1. HackerRank

HackerRank is a technical assessment and remote interview solution for hiring developers. Above all, you can practice problems in Frontend, algorithms, and data structures in a variety of languages.

2. LeetCode

Similarly to HackerRank, LeetCode is a huge repository of real interview questions asked by the most popular tech industries. Moreover, a great resource to level up your problem-solving skills.

3. Geekforgeeks

An online portal that goes through several computer science concepts and also includes a step-by-step preparation guide, as well as company-specific preparation guides.

4. The System Design Primer

The System Design Primer is a free GitHub repository created by Donne Martin, an engineer at Facebook.

5. is a premium resource that pairs you anonymously with real engineers from the industry to practice your interviewing skills.

6. Grokking Algorithms

Grokking Algorithms is a fully illustrated, friendly guide that teaches you how to apply common algorithms to the practical problems you face every day as a programmer.

Also, check out Grokking Algorithms here

7. Cracking the coding interview

This is a deeply technical book and focuses on the software engineering skills to ace your interview. Firstly, it will teach you how to solve problems. Secondly, it will make your programming basics strong.

Also, you can buy this book at the best price here

That’s it for this post guys, these are the frequently asked OOPs Interview questions. I hope you liked it and learned something new from this article. In conclusion, these are some of the most important topics to ace interviews. Moreover, if you have any queries feel free to leave a comment below.

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