Object-Oriented Programming (OOPs) is a fundamental concept that every developer should understand, regardless of their programming language of choice. OOPs allows developers to create complex, scalable, and reusable code that can be easily maintained and adapted over time.
However, mastering OOPs is no easy feat, and it's not uncommon for job seekers to face a barrage of OOPs interview questions during the hiring process.
In this post, we'll cover the top interview questions of OOPs that you're likely to face during a technical interview and provide insights into how you can answer them to showcase your knowledge and skills.
So, whether you're a seasoned developer looking to brush up on your OOPs skills or a job seeker preparing for an upcoming interview, read on to learn more!
Interview Questions on OOPs for Freshers
1. What is OOPs?
It is a programming paradigm that is used to develop software applications by creating objects that interact with each other.
In simple terms, OOP is a way of writing software that models real-world objects, such as people, cars, or buildings, as software objects with specific properties and behavior.
The main idea behind OOP is to create reusable code that can be modified and extended with ease. It allows programmers to write code that is easier to read, understand, and maintain.
2. What are the key principles of OOPs?
It is one of the most asked interview questions on OOPs concepts. You must know that there are four principles of OOP using which developers can write code more efficiently and maintain it with ease.
a) Encapsulation
It is used to hide the internal details of an object and its behavior from the outside world.
This allows objects to be used and manipulated without revealing their internal workings. Encapsulation is achieved by defining the object's attributes as private or protected and providing public methods to access and modify those attributes.
b) Inheritance
It is the process of creating new classes from existing classes. It allows a new class to inherit properties and behavior from an existing class.
The existing class is known as the superclass or parent class. The new class is known as the subclass or child class.
c) Polymorphism
It is the ability of an object to take on multiple forms. It allows different objects to be used interchangeably, even though they may have different implementations. Polymorphism can be achieved through method overloading and method overriding.
d) Abstraction
It is the process of simplifying complex systems by modeling them at a high level. In OOP, abstraction is achieved by creating abstract classes and interfaces that define the methods that must be implemented by their subclasses.
This allows the programmer to focus on the essential features of the system while ignoring the irrelevant details.
3. What is a class in OOPs?
It is a blueprint or a template for constructing objects. It is used to define a set of properties and methods that will be present in an object belonging to that class.
It is essentially a user-defined data type that encapsulates data (in the form of fields or properties) and behavior (in the form of methods). The fields or properties define the characteristics of the object, while the methods define what the object can do.
Example of class:
Let's consider a class called "Car". This class may have fields such as "make", "model", "year", and "color", which define the characteristics of a car object.
It may also have methods such as "start", "stop", "accelerate", and "brake", which define the behavior of a car object.
Once a class has been defined, it can be used to create multiple instances or objects of that class. Each object will have its own set of values for the fields or properties and will be able to perform the methods defined by the class.
4. What is an object in OOPs?
An object is an instance of a class. It is a concrete entity that can be created based on a class blueprint.
When an object is created, it has its own unique set of properties and methods based on the definition of its class. These properties and methods can be accessed and manipulated through the object's public interface, which consists of its public methods and properties.
Example of object:
Consider the class "Car". An object of the Car class can be created by instantiating the class, like this:
Car myCar = new Car();In this case, myCar is an object of the Car class. It has its own set of properties (such as make, model, year, and color) and methods (such as start, stop, accelerate, and brake) that are defined by the Car class. These properties and methods can be accessed and manipulated using dot notation, like this:
myCar.color = "red";
myCar.start();5. What is inheritance in OOPs?
This is among the top OOPs questions for the interview.
Inheritance is the process of creating a new class (called the subclass or child class) from an existing class (called the superclass or parent class).
The subclass inherits properties and behaviors from its superclass, and can also add new properties and behaviors or modify existing ones.
The basic idea behind inheritance in OOP is to create a hierarchy of classes with increasing levels of specialization. The most general class in the hierarchy is the superclass, which defines the basic properties and behaviors that are shared by all its subclasses. Each subclass can then add more specific properties and behaviors that are unique to it.
Example of inheritance in OOP:
Consider a class hierarchy that includes a superclass called "Vehicle" and two subclasses called "Car" and "Motorcycle". The Vehicle class may have properties such as "make", "model", "year", and "color", as well as methods such as "start" and "stop" that are common to all types of vehicles.
The Car subclass may inherit these properties and methods from the Vehicle class, but also add its own properties, such as "numDoors" and methods such as "getGasMileage". The Motorcycle subclass may also inherit from Vehicle, but may have its own unique properties such as "numWheels" and methods such as "lean".
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6. What is encapsulation in OOPs?
Encapsulation is the concept of hiding the implementation details of a class from its users, and providing a public interface or API (Application Programming Interface) for interacting with the class.
The idea behind encapsulation is to protect the internal state of an object from being modified directly by external code, and to enforce the use of the public interface for any interactions with the object. This helps to prevent errors and ensure that the object is used correctly.
Example of encapsulation:
Consider a class called "BankAccount". This class may have private fields such as "balance" and "accountNumber", which should not be modified directly by external code. Instead, the class may provide public methods such as "deposit", "withdraw", and "getBalance" for interacting with the account.
7. What is an abstraction in OOPs?
It is the process used to define a simplified interface or model that represents the essential features of an object, without including unnecessary details or implementation specifics.
Abstraction helps to manage complexity by hiding the underlying details of a system and presenting only the essential features that are relevant to the user. This allows the user to interact with the system at a higher level of abstraction, without having to worry about the low-level details.
An abstract class may contain one or more abstract methods, which are defined but not implemented in the abstract class. The subclasses of the abstract class must implement these abstract methods to provide concrete functionality.
Example
For example, consider a class hierarchy that includes a superclass called "Animal" and two subclasses called "Dog" and "Cat".
The Animal class may have abstract methods such as "makeSound" and "move", which are implemented differently in each subclass. The Dog subclass may implement the "makeSound" method as "bark" and the "move" method as "run", while the Cat subclass may implement the "makeSound" method as "meow" and the "move" method as "walk".
8. What is polymorphism in OOPs?
Polymorphism is a fundamental concept in Object-Oriented Programming (OOP) that allows objects of different classes to be treated as if they are objects of a common superclass or interface.
It enables the same code to work with different objects in different ways, depending on their actual type or class.
9. What is method overloading? Explain with an example.
It is a form of static polymorphism that allows multiple methods to have the same name but with different parameters or argument types.
When an overloaded method is called, the compiler determines which method to call based on the number, type, and order of the arguments passed to the method. The method name and the number, type, and order of the parameters must be different in each overloaded method.
Example of method overloading in OOPs
For example, consider a class called "Math" that contains two overloaded methods called "add".
The first method takes two integers as arguments and returns their sum, while the second method takes two doubles as arguments and returns their sum.
When we call the "add" method with two integers, the first method is called, and when we call the "add" method with two doubles, the second method is called.
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Frequently Asked Questions
Ace your job interview with these oops interview questions for both freshers and experienced developers. Get prepared with an expert guide. This guide provides structured insights, proven methodologies, and actionable execution steps for modern professionals.
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