Interview Success: Top 10 Object Oriented Programming Questions You Must Know

Interview Success: Top 10 Object Oriented Programming Questions You Must Know

Are you preparing for an interview that involves questions on Object-Oriented Programming (OOP)? Then you’ve come to the right place! OOP is a popular programming paradigm used in many software development companies, and employers often test candidates’ knowledge of OOP concepts during interviews. In this blog post, we will cover the top 10 essential OOP questions that every candidate should know. By mastering these concepts, you’ll be better equipped to impress your interviewer and land your dream job. So let’s dive into the world of object-oriented programming!

What is Object-Oriented Programming (OOP)?

Object-Oriented Programming (OOP) is a popular programming paradigm that aims to organize code in a more structured and efficient way. In OOP, code is organized into objects, each of which contains data and functions that operate on that data.

One of the main advantages of using OOP is its ability to improve code reusability. Instead of writing repetitive pieces of code throughout an application, developers can create reusable classes and objects that can be called upon whenever necessary.

Another key benefit of OOP is its ability to enhance program security by encapsulating data within objects. This means that sensitive information or methods cannot be accessed without proper authorization, improving overall system security.

Essentially, OOP promotes modular design patterns in software development by breaking down complex systems into smaller parts that are easier to manage and maintain over time. Mastering these concepts will not only help you ace your interview but also make you a better developer in the long run!

What is the difference between a class and an object?

Object-oriented programming revolves around the concepts of classes and objects. A class is a blueprint or template that defines the attributes and behaviors common to all instances of that class. On the other hand, an object is an instance of a particular class.

In simpler terms, imagine a class as a cookie cutter, while an object is the actual cookie produced by using that cookie cutter. The cookie cutter specifies how the cookies should look like but doesn’t have any unique characteristics until it’s used to create cookies.

A class can be considered as a user-defined data type, which means it creates its own data type with specific properties and methods. Objects are created from these predefined classes and inherit their attributes and behaviors.

It’s important to note that multiple objects can be created from one single class, each possessing its own values for variables defined in the constructor method of the respective object.

In summary, while classes define common attributes and behavior for all objects within them (similar to templates), objects represent individual entities with distinct information within those predefined structures.

What is the difference between method overloading and method overriding?

When discussing object-oriented programming, it’s important to understand the difference between method overloading and method overriding.

Method overloading occurs when a class has multiple methods with the same name but different parameters. This allows for flexibility in coding as it enables developers to use the same method name for different functionalities without needing to create new names each time.

Method overriding, on the other hand, occurs when a subclass provides its own implementation of a method that is already defined in its superclass. This allows for further customization and specialization of classes while still maintaining consistency within an inheritance hierarchy.

One key distinction between these two concepts is that method overloading pertains to methods within the same class or interface, while method overriding involves methods across different classes or interfaces within an inheritance hierarchy.

While they may seem similar at first glance, understanding these differences can greatly improve one’s ability to write efficient and effective code in object-oriented programming environments.

What is inheritance?

Inheritance is a fundamental concept in Object-Oriented Programming that allows classes to inherit properties and behaviors from other classes. This means that a class can be created based on an existing class, known as the parent or base class.

Inheritance provides code reusability by allowing subclasses to reuse common functionality of their parent class. The subclass can modify or extend its inherited methods and properties according to its specific needs.

There are different types of inheritance such as single, multiple, hierarchical and hybrid inheritance. Single inheritance refers to only one parent class for each child class whereas multiple inheritance allows a child class to inherit properties from more than one parent classes.

Hierarchical Inheritance involves creating several related sub-classes using a single base (parent)class while Hybrid Inheritance combines two or more types of inheritance in one program.

Understanding the basics of inheritance is crucial for Object Oriented programming success since it helps developers create efficient code with less repetition while enhancing modularity and maintainability.

What is an abstract class?

An abstract class is a type of class that cannot be instantiated. It serves as a base for other classes to inherit from and provides common functionality for its subclasses. One of the defining characteristics of an abstract class is that it can contain both concrete methods and abstract methods.

Abstract methods are declared but not defined in the abstract class, leaving their implementation up to the subclass. This allows each subclass to provide its own specific implementation while still inheriting shared behavior from the abstract superclass.

Another important aspect of an abstract class is that it cannot be used on its own like a regular class. Instead, it must be subclassed and implemented before it can be used in code.

Understanding how to work with abstract classes is key when working with object-oriented programming concepts. They allow developers to create flexible architectures and reusable code by providing shared functionality through inheritance while still allowing for customization through individual implementations in subclasses.

What is the difference between an interface and an abstract class?

When it comes to Object-Oriented Programming (OOP), both interfaces and abstract classes are used as blueprints for creating objects. However, there is a difference between these two concepts.

An abstract class can contain both concrete and abstract methods that must be implemented in the subclass. This means that an abstract class can provide some default implementation while allowing subclasses to override certain behaviors.

On the other hand, an interface only defines method signatures without providing any implementation details. In simpler terms, an interface acts as a contract where all its methods must be implemented by any class that implements that interface.

Another key difference between the two is that a class can extend only one abstract class but implement multiple interfaces. Additionally, since Java doesn’t support multiple inheritance of classes with concrete method implementations; using interfaces becomes more flexible when attaching behavior to a given object.

In summary, while both concepts aim at achieving abstraction and creating modular code within OOP projects; they take different approaches in defining how the actual implementation should happen.

What is a package?

In object-oriented programming, a package is simply a way of organizing related classes and interfaces together. It helps in avoiding naming conflicts between classes and provides better accessibility to the class files.

A package can be seen as a container that holds different types of classes and interfaces. It allows us to group related code into one module so that it is easier to manage and maintain.

The main advantage of using packages is that they provide an additional level of encapsulation. By grouping similar functionality together, we can hide the complexity of our code from other parts of the program.

When we create a new package, we need to give it a unique name. The convention for naming packages is usually based on the reverse domain name system (DNS) used by websites – starting with your company’s domain name in reverse order.

In Java, for instance, all standard library classes come under java.lang or When you import these packages at the top of your file, you gain access to their contents within your own program’s source code.

Understanding how packages work is essential when working with large projects or teams where multiple developers may be working on different parts of the same application simultaneously.

What is aggregation?

Aggregation is an object-oriented programming concept that defines a relationship between two classes. It refers to the process of combining multiple objects or instances of one class within another class. The main purpose of aggregation is to create more complex and meaningful objects by grouping simpler ones.

One way to think about aggregation is through the analogy of a car and its components. A car consists of various components such as tires, engine, seats, etc. Each component can exist independently but they come together to form a complete car. Similarly, in programming, we can have different classes that represent these individual components and then group them into a single class using aggregation.

The key feature in aggregation is that the aggregated objects can be shared among multiple instances of the aggregating class. This means that if there are 10 instances of Class A and each instance has an object from Class B as part of its composition then all those 10 instances will share the same object from Class B.

Aggregation also enables us to reuse code by creating modular designs where we can easily plug-and-play different modules based on our needs without having to change much code in other parts of our program. Understanding this concept is crucial for building scalable and maintainable software systems with reusable components at their core.

What is composition?

Composition is an essential OOP concept that allows developers to create complex objects by combining simpler ones. In composition, one class holds a reference to another class and uses its functionality to achieve a specific task.

Composition works by aggregating or assembling multiple classes into one object. The composed object can then be used as any other object in the program, including being passed around between different functions.

One of the advantages of using composition over inheritance is that it provides better flexibility and modularity. With composition, individual objects can be easily swapped out or modified without affecting the entire system’s behavior.

For example, suppose we have separate classes for engine, wheels, brakes and suspension systems in a car simulation game. By composing these classes together into a Car class, we can create various types of cars with different combinations of these components quickly.

Composition is an important concept in Object Oriented Programming that enables developers to build complex systems from smaller parts efficiently. It promotes reusability and maintainability while providing more flexibility than inheritance alone.


Object-oriented programming is an essential concept that every developer must familiarize themselves with. Whether you are a beginner or experienced programmer, understanding the basics of OOP and being able to answer interview questions related to it can significantly increase your chances of landing that dream job.

In this article, we have covered ten critical OOP interview questions that you should know. We hope these questions have provided you with a solid foundation for your upcoming interviews and given you the confidence needed to excel in any technical assessment.

Remember, practice makes perfect! The more you work on coding exercises and solve problems related to OOP concepts, the better prepared you will be when it comes time for your next interview. So keep practicing, stay motivated, and good luck out there!