Top 20+ OOP’s Interview Questions and Answers

  • By Deepali Shinkar
  • August 16, 2023
  • JAVA
Top 20+ OOPs Interview Questions

Top 20+ OOP’s Interview Questions and Answers

Object-Oriented Programming (OOP) is a programming paradigm that revolves around the concept of “objects” and their interactions to model and solve real-world problems in software development. OOP aims to organize code in a structured, modular, and reusable manner. It is widely used in modern programming languages like Java, Python, C++, and more. In this particular blog, we will discuss more Top 20+ OOP’s Interview Questions and Answers.


Top 20+ OOP’s Interview Questions and Answers

Q.1 What are OOPs? 

OOPs, or Object-Oriented Programming is a programming model or paradigm which  revolves around the concept of “OBJECTS”. 

It provides a means of structuring programs so that properties and behaviors are  bundled into individual objects. 

For instance, an object could represent a person with properties like a name, age,  and address and behaviors such as walking, talking, breathing, and running. 

In fact, the OOPs model is so popular, that many of the most widely used  programming languages support and use this Object Oriented Programming or  OOPs model, such as Java, C++, Python, C#, PHP, Javascript, etc. 

Q.2 What is the purpose of OOPs? 

There are numerous reasons why OOPs are commonly used, however the following  are the most important:  

  • OOPs allows people to readily grasp software even if they are unfamiliar with the underlying implementation.
  • OOPs, improve the readability, understandability, and maintainability of code by a factor of ten.
  • Using OOPs, even large software may be simply built and controlled.

Q.3 What are the main features of OOPs?

OOPs or Object Oriented Programming mainly comprises of the below four features,  and make sure you don’t miss any of these: 

  1. Inheritance
  2. Encapsulation
  3. Polymorphism
  4. Data Abstraction

Q.4 What is class? 

Class is basically a User-defined blueprint from which objects are created. It consists  of methods ( set of instructions) that are performed on the objects. 

Q.5 What is an object? 

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

Q.6 What is inheritance? 

Inheritance is a feature of OOPs that allows classes to inherit common properties from other classes. For example, if there is a class such as ‘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.

Q.7 What are the different types of inheritance? 

  • Single inheritance 
  • Multiple inheritance 
  • Multilevel inheritance 
  • Hierarchical inheritance 
  • Hybrid inheritance 


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Q.8 What is a superclass? 

A superclass or base class is a class that acts as a parent to some other class or class. For example, the Vehicle class is a superclass of class Car. 

Q.9 What is a subclass? 

A class that inherits from another class is called the subclass. For example, the class  Car is a subclass or a derivation of the Vehicle class. 

Q.10 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. This method will be defined in the subclasses with different definitions for different vehicles.

Q.11 What is method overloading? 

There is a concept where two or more methods can have the same name. But they should have different parameters, different numbers of parameters, different types,  or both. These methods are known as overloaded methods and this feature is called method overloading. 

Q.12 What is method overriding? 

Method overriding is a concept of object-oriented programming. It is a language feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its superclasses or parent classes. 

Q.13 What is static polymorphism? 

Static polymorphism (static binding) is a kind of polymorphism that occurs at compile time. An example of compile-time polymorphism is method overloading.

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Q.14 What is dynamic polymorphism? 

Runtime polymorphism or dynamic polymorphism (dynamic binding) is a type of polymorphism that is resolved during runtime. An example of runtime polymorphism is method overriding. 

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Q.15 What is Encapsulation?

Encapsulation refers to binding the data and the code that works on that together in a single unit. For example, a class. Encapsulation also allows data hiding as the data specified in one class is hidden from other classes. 

Q.16 What is data abstraction? 

Data abstraction is a very important feature of OOPs that allows displaying only the important information and hiding the implementation details. For example, while riding a bike, you know that if you raise the 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. 

Q.17 How to achieve data abstraction? 

Data abstraction can be achieved through: 

  • Abstract class 
  • Abstract method 

Q.18 What is an abstract class? 

An abstract class is a class that consists of abstract methods. These methods are basically declared but not defined. If these methods are to be used in some subclass,  they need to be exclusively defined in the subclass. 

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Q.19 Can you create an instance of an abstract class?

No. Instances of an abstract class cannot be created because it does not have a  complete implementation. However, instances of subclass inheriting the abstract class can be created. 

Q.20 What is a constructor? 

A constructor is a special type of method that has the same name as the class and is used to initialize objects of that class. 

Q.21 What is a destructor? 

A destructor is a method that is automatically invoked when an object is destroyed.  The destructor also recovers the heap space that was allocated to the destroyed object, closes the files and database connections of the object, etc. 

Q.22 Types of Constructors 

Types of constructors differ from language to language. However, all the possible  constructors are: 

  • Default constructor
  • Parameterized constructor
  • Copy constructor
  • Static constructor
  • Private constructor


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Q.23 What various sorts of Python methods are there? 

The class has three distinct kinds of methods. All of the class activities are carried out with these techniques. 

  • Instance Methods 
  • Class Methods 
  • Static Methods

Q.24 What does Python’s Super Method mean? 

The super() function is used to give access to methods and properties of a parent or sibling class. The super() function returns an object that represents the parent class. The super() function in Python makes class inheritance more manageable and extensible. The function returns a temporary object that allows reference to a parent class by the keyword super. 

There are two important things: 

child class static method and class method: we cannot use super() directly. child class: not allowed to access instance variables(parent class) by using super(). 

Q.25 What does Python’s MRO (Method Resolution Order)  mean? 

Method Resolution Order is referred to as MRO. A class inherits from many classes under multiple inheritance. If we attempt to access a method by building an object from the child class, the methods of the child class are first searched for the method.


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