OOPS interview questions and Answers

Last updated on Jan 04, 2023
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OOPS interview questions

OOPS, i.e. Object-Oriented Programming Language is one of the most important concepts which is widely used in the programming world. Every interview that you are attending today requires the knowledge of OOPS. The below article compiles the most frequently asked OOPS Interview Questions and Answers which help you to ace your interviews. If you don’t know object-oriented programming then you can’t think of developing mobile software. Its unique features like inheritance, data hiding which is also known as encapsulation, data binding, polymorphism make it superior to other programming languages.

Popular languages like Java, C++, and Python, etc. are using the concept of the oops model and making it more significant in the programming world. Through OOPs a user can break his program into small-sized problems and that can be solved easily like one object at one time. The system in which the concept of OOP is used can be easily upgraded and hence provides better quality of software, enhances programmer productivity, and lower maintenance cost.

Object Oriented Programming Interview Questions

Here in this article, we will be listing frequently asked OOPS interview questions and Answers with the belief that they will be helpful for you to gain higher marks. Also, to let you know that this article has been written under the guidance of industry professionals and covered all the current competencies.

Q1. Why is object-oriented programming so popular?

There are certain points due to which OOPs become so popular.

  • It provides a better programming style, so you don’t need to write code again and again which you want to run, just make a class of the object and call it.
  • As it supports the inheritance concept, an application created with OOPs can inherit another class property.
  • It provides a modularity model that means if you change any part of code that is in a separate module, that won’t impact any other module.
  • If you are stuck somewhere, this language allows your problems to break down into bite-sized pieces so that you can solve them.
  • Due to its polymorphism feature, a single class can be used to create different objects, and that too from the same piece of code.
Q2. What is Class and Objects in OOPS?


In Object-Oriented Programming, a class is a blueprint that defines the functions and variables which are common to objects of a certain kind.


In OOPS an object is a specimen of the class. It is nothing but a component that consists of methods and properties which make the data useful and help users to determine the behavior of the class.

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Let’s understand this with an example

class Person{

    public $name;

    function __construct($name){

        $this->name = $name;


    function getUserDetails(){

        return "My name is ".$this->name;



Q3. What are the types of Class Variables?

We have three different types of Class Variables in OOPs.

1. Local Variables

These types of variables are declared locally in methods, blocks, and constructors. These variables are created when program control enters the methods, blocks, and constructor and are destroyed once program control leaves them.

2. Instance Variables

These variables are declared outside a block, constructor, or method. These are created once a class object is created and destroyed when the object is destroyed.

3. Static Variables

Static variables are also called class variables and are defined using the static keyword. These are declared within a class but outside a code block and a method. The creation of these variables starts when the program starts and is destroyed when the program ends.

Q4. What is the difference between Method overriding and Method overloading?
Method Overloading Method Overriding
It is the concept where we define two or more methods by the same name but with different signatures. In method overriding we define two or more identical methods which have the same name and signatures.
The binding of the method is done at compile time. The binding of the method is done at run time.
There are no class restrictions i.e. it can be achieved in the same or different classes. There are class restrictions in it i.e. it can only be achieved in different classes.
Q5. What is virtual and pure virtual function?
Virtual Function Pure Virtual Function
Virtual Function has its definition hidden in the Base class They have no definition in the Base class.
The derived class can override the virtual function if required. In the case of a pure virtual function, the derived class has to override it.
If the derived class fails to override then it has the option to use the virtual function of the base class It will throw a compilation error if it fails to override pure virtual function.
Q6. List out some of the differences between a class and an object?
It is a blueprint from which different instances (objects) are created. Objects are the instances of the class.
Class is a logical entity. Objects are physical entities.
Users can declare class only once. Objects can be declared multiple times depending upon the requirements.
When a class is created there is no memory allocation Objects allocated memory.
Class is a group of objects. Objects are real-world entities such as pen, copy, mouse, etc.
Class can be declared using class keyword e.g class Student {} Objects can be declared using the new keyword e.g. Student s1=new Student();
Q7. What are the main features of OOPs?

You have to list these four features of OOPs while answering this question-

  • Inheritance
  • Polymorphism
  • Encapsulation
  • Data Abstraction
Q8. What is Encapsulation in oops with an example?

The process of binding up data and functions together that manipulates them is known as encapsulation in OOPS. It protects the data from outside interference and misuse.

Let’s understand the concept of encapsulation with both real-world examples and with the help of a program.

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It is an attribute of an object, and it contains all data which is hidden. That hidden data is restricted to the members of that class.

class Account {
    private int account_number;
    private int account_balance;

    public void show Data() {
        //code to show data

    public void deposit(int a) {
        if (a < 0) {
            //show error
        } else
            account_balance = account_balance + a;

Q9. What is Polymorphism and its types in OOPS?

Polymorphism is one of the core concepts which is used in object-oriented programming. Polymorphism generally shows the relationships between parent class objects and child class objects.

Types of polymorphism in OOPs

  • Compile Time Polymorphism- It is also known as Static Binding and allows the programmer to implement various methods. Names can be the same but their parameters should be different.
  • Runtime Polymorphism- It is also known as Dynamic Binding and allows the programmer to call a single overridden method during the runtime of the program.
Q10. What is Inheritance?

It is a technique in which one class acquires the property of another class. With the help of inheritance, we can reuse the fields and methods of the existing class.

Inheritance has three type, are given below.

  • Single inheritance
  • Multiple inheritance
  • Multi level inheritance

But PHP supports only single inheritance, where only one class can be derived from single parent class. We can also use multiple inheritance by using interfaces.


Object-Oriented Programming is a very vast concept and takes some time to master. Going only through these object-oriented programming interview questions won't help you. You have to brush up your mind by practicing more and more programming questions to keep you updated and to get a better understanding of OOPS concepts.

Let me give you a short and smart trick to crack these types of interviews. Whenever you look at any real entities try to relate them with the OOPS concept and try to find their methods, attributes. In this way, programming is more enjoyable and easier.

Reviewed and verified by Umesh Singh
Umesh Singh

My name is Umesh Singh having 11+ experience in Node.JS, React JS, Angular JS, Next JS, PHP, Laravel, WordPress, MySQL, Oracle, JavaScript, HTML and CSS etc. I have worked on around 30+ projects. I lo...