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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.
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.
OOPs, allow clarity in programming, therefore, allowing simplicity in solving complex problems.
Also Read: JavaScript Higher Order Functions Explained
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.
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.
Class | Structure |
User-defined blueprint from which objects are created. It consists of methods or set of instructions that are to be performed on the objects | A structure is basically a user-defined collection of variables that are of different data types |
Object-Oriented Programming | Structural Programming |
Object-Oriented Programming is a type of programming that is based on objects rather than just functions and producers | Provides logical structure to a program where programs are divided functions |
Bottom-up approach | Top-down approach |
Provides data hiding | Does not provide data hiding |
Can solve problems of any complexity | Can solve moderate problems |
Code can be reused thereby reducing redundancy | Does not support code reusability |
Yes, you can call the base class without instantiating it if:
Object | Class |
A real-world entity which is an instance of a class | A class is basically a template or a blueprint within which objects can be created |
An object acts like a variable of the class | Binds method and data together into a single unit |
An object is a physical entity | A class is a logical entity |
Objects take memory space when they are created | A class does not take memory space when created |
Objects can be declared as and when required | Classes are declared just once |
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.
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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.
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.
Data Abstraction | Encapsulation |
Solves the problem at the design level | Solves the problem at the implementation level |
Allows showing important aspects while hiding implementation details | Binds code and data together into a single unit and hides it from the world |
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.
Error | Exception |
Errors are problems that should not be encountered by applications | Conditions that an application might try to catch |
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.
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Name | Accessibility from own class | Accessibility from derived class | Accessibility from world |
Public | Yes | Yes | Yes |
Private | Yes | No | No |
Protected | Yes | Yes | No |
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.
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.
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Multiple Inheritance | Multilevel 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. |
Hybrid inheritance is a combination of multiple and multiple-level 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.
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.
Overloading | Overriding |
Two or more methods having the same name but different parameters or signature | Child class redefining methods present in the base class with the same parameters/signature |
Resolved during compile time | Resolved during runtime |
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.
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.
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.
The System Design Primer is a free GitHub repository created by Donne Martin, an engineer at Facebook.
Interviewing.io is a premium resource that pairs you anonymously with real engineers from the industry to practice your interviewing skills.
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
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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