Top 50+ OOPs Interview Questions and Answers in 2024

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Importance of OOPs Interview:

In this 21st-century, the era of digitalization, the modern-day world is flourishing with digital platforms along with the humungous amount of digital content scattered everywhere. Therefore, the digital world requires coding and programming more than ever to find a sequence of instructions that’ll automate the performance of any task on a computer or a digital medium. Programming is often used to solve given problems regarding operating systems, desktop applications, web applications, web services, game development, etc. Here comes OOPs or the Object-Oriented Programming system to serve the 21st-century digital need. This makes the recruiters take up OOPs interview in the programming domain. Let’s discuss how the wide range of OOPs usage makes OOPs Interview essential for the candidates.

Now, Let’s jump into our main objective of the blog, i.e. over fifty most relevant interview questionnaires for the OOPs interviews that can be asked in 2022.

Top 52 most important questions with relevant answers for OOPs Interview:

Here we’ll be discussing the OOPs interview question segmented into several categories based on the types and topics of the questions asked

Basic OOPs Interview Questions with Answers designed for the freshers:

1. What are OOPs?

OOPs is the Object-Oriented Programming system. In OOPs the programs are considered as a collection of objects. We can define an object as an instance of a particular class.

2. What are the differences between OOPs and SOP?

The fundamental differences between OOPs and SOP are-

OOPs	SOP
It is Object-Oriented Programming.	It is Service-Oriented Programming, which is structural programming.
Rather than just functions and procedures, OOPs is a type of programming that is based on objects.	Whereas SOP provides a logical structure to a program. And in this case, programs are divided into different functions.
It works with a Bottom-up approach.	It works with a Top-down approach.
OOPs provides us with the feature of data hiding.	Whereas, SOP does not provide such a feature.
It can solve problems of any complexity level.	It can solve only moderate problems.
In OOPs programming, code can be reused. So, it reduces redundancy.	SOP programming does not support the reusability of codes.

3. Describe OOPs programming in short?

OOPs or Object-Oriented Programming is a type of programming based on objects. It does not depend only on the functions and procedures of the process. In this programming system, Individual objects are sorted into different classes based on their characteristic features. OOPs programming executes real-world entities such as abstraction, inheritance, polymorphism, encapsulation, etc. into the programming system. It also allows the data to bind with its complementary code.

4. What are the four main pillars of OOPs?

The four main key features of OOPs programming are-

• Data Abstraction
• Inheritance
• Encapsulation
• Polymorphism

5. Discuss the advantages of using OOPs programming.

• Using OOPs we can solve complex problems with ease. Because it provides clarity and simplicity in the programming system with its organizing key features.
• Working on the OOPs programming system, we can reuse codes through inheritance, reducing redundancy.
• Here, the data are bound with its complementary code by encapsulation. This provides clarity to the database.
• The OOPs give us the feature of data hiding, because of which the private data can be kept confidential.
• Using OOPs, the problems can be divided into different sections using the classes which makes them simple to solve.
• The polymorphism, one of the key features of the OOPs system, provides flexibility to the program as it allows the entities to have multiple forms at a time.

OOPs Interview Questions and Answers on Classes and Objects:

6. What is a class in terms of OOPs programming?

A class is a template consisting of objects each of which is in different states and portrays different behaviors. It has many methods by which the objects can be instructed or commanded to get sorted within a particular class.

7. Differentiate a class from a structure?

The basic difference between a class and a structure is as follows:

Class	Structure
A class is a blueprint defined by the user because the objects are created from it. It includes methods. Methods is a set of instructions. These instructions are to be performed on the objects in the class.	A structure, however, is a collection of different data type variables defined by the users.

8. In which circumstances can you call the base class method without creating an instance?

We can call the base class without creating an instance if:

• It is a static method only.
• The prime class is taken over by another subclass through the process of inheritance.

9. What is an object in Programming?

An object is a real-world entity. It is the basic unit of the OOPs programming system. Different objects differ in their respective states and show behavioral characteristics. For example, a bobby pin, a chair, a dog, etc. have different states or attributes with different behavioral aspects. Similar objects are grouped into particular classes based on these characteristic features.

10. State the basic differences between a class and an object?

The differences between a class and an object are as follows:

Object	Class
An object is a basic real-world entity and also an instance of a particular class.	Whereas, a class is a base or a blueprint within which we can create and classify the objects.
An object serves as a fluid component of a particular class.	In the class, several methods bind the code and the data it is structured for, together into a single unit.
An object is a physical as well as a logical entity.	A class, however, is only a logical entity.
Objects take up memory space in the programming system when they are created.	Though, the classes do not take up any memory space when they are created in the program.
The Objects are declared whenever it’s required.	Whereas, the classes can be declared only once.

OOPs Interview Questions and Answers on Abstraction:

11. What is Abstraction in the OOPs programming system?

Abstraction is a fundamental technique in OOPs using which we can hide the non-essential data to provide more efficiency to the users. Abstraction hides all nonrequired data aiming to let the users work with the essential data only. This feature provides more clarity and efficiency of the system to the programmers.

12. How can you implement Abstraction while programming?

There are two efficient ways to achieve abstraction while programming. These are as follows:

1. By Abstract class, i.e., 0 to 100% accurate.
2. Through Interface i.e., 100% efficient.

13. Differentiate between abstract class and concrete class?

There are mainly two differences between an abstract class and a concrete class. These are as follows:

Abstract Class	Concrete Class
We cannot create Objects from an abstract class.	Objects can only be created of their non-abstract or concrete subclass.
An abstract class can have zero to several methods to instruct the objects.	Whereas, for non-abstract or concrete classes, such features are not allowed.

14. Are abstract modifiers applicable for the variables?

No. We cannot apply abstract modifiers to the variable objects in a program.

15. Can you declare an abstract method with a private modifier?

No. The abstract methods cannot be private because they must be implemented in the subclass and not in the superclass. If we declare it with a private modifier, we won’t be able to implement it from outside the class.

OOPs Questions and Answers on Inheritance:

16. What is inheritance in the OOPs programming system?

Inheritance is a key feature of the OOPs programming system. It allows classes to inherit common or similar properties from other classes. For example, if there is a class such as ‘books’, and there are other classes like ‘fiction’, ‘nonfiction’, etc, then these other classes can inherit the common properties from the ‘book’ class. This feature helps us eliminate or reduce redundant code. So, it reduces the entire size of the code as well.

17. What is superclass in OOPs?

A superclass as known as a base class is what acts as a parent class to some other class or classes. For example, the ‘house’ class is a parent class of classes like ‘bedroom’, ‘kitchen’, ‘porch’, etc.

18. What is a subclass in OPPs programming?

A subclass is a class that inherits similar properties from another class. For example, the ‘kitchen’ class is a subclass as well as a derivative of the ‘house’ class.

19. State the different types of inheritance?

The different types of inheritance are as follows:

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

20. Differentiate multiple and multilevel inheritances with examples.

The basic differences between multiple and multilevel inheritances are-

Multiple Inheritance	Multilevel Inheritance
Multiple inheritances are considered when a class takes over more than one base class.	Multilevel inheritance, however, comes into a complex picture when a class takes up common properties from another class and this other class itself is a subclass of some other base class.
Example: A class that defines ‘cushions’ can inherit from two base classes like ‘bedroom’ and ‘living room’.	Example: A class that describes ‘cushion’ will inherit from a base class ‘living room’ which in turn inherits or is a subclass of another base class ‘house’.

21. Define hybrid inheritance.

A combination of multiple inheritance and multi-level inheritances is known as a Hybrid Inheritance.

22. Describe hierarchical inheritance.

The hierarchical inheritance is where one base class has more than one subclasses under it. For example, the ‘house’ class can have ‘bedroom’, ‘kitchen’, ‘living room’  etc as its subclasses.

23. Discuss the limitations of inheritance in OOPs programming.

There are certain limitations of inheritance. Such as-

• Because working with inheritance requires frequent shifting between different classes. It expands the time limit and the efforts required to execute a program through OOPs. 
• Using inheritance the Superclass and the Subclass get so strongly coupled that sometimes it’s difficult to acquire their individual properties.
• If we make any modifications to the program, we’d have to make changes both in the parent and the child class as well.
• To avoid incorrect results, we have to be very careful with each implementation of objects.

24. What is the fundamental difference between Abstraction and Inheritance?

The principal difference between inheritance and abstraction is-

Abstraction.	Inheritance.
It is an object-oriented concept. We can simplify things in programming by abstracting details. It mostly helps us to design a system.	Whereas, Inheritance allows us to reuse codes. We can reuse the functionality we’ve already coded with the help of Inheritance.

25. Explain what will happen in the given scenario: a class extends two interfaces both of which have a method with the same name and same signature.

In the provided circumstances, a conflict will arise. Because the compiler won’t be able to link a method call due to the obscurity. Thus, we’ll get a compile-time error in this case.

OOPs Questions and Answers on Encapsulation:

26. Define encapsulation.

Encapsulation is the process of binding data with its code that works on it, within a single unit. It also ensures data-hiding by specifying the data in one class and hiding it from another class.

27. What are the ‘access specifiers’ in OOPs programming?

The access specifiers as known as access modifiers are the keywords. They determine the accessibility of classes, methods, etc in OOPs. These allow the execution of encapsulation. Commonly used access modifiers are private, protected, and public. However, there are some programming language-specific modifiers as well.

28. Explain a tightly encapsulated class.

When each variable is declared private in the class using a private modifier, it is called a tightly encapsulated class.

29. What is an interface?

An Interface is a concept that let users declare methods without defining them. Though interfaces are not blueprints like classes because they don’t hold detailed actions or instructions to be performed on the objects. However, if a class implements an interface, defines the methods of the interface as well.

30. What are the differences between data abstraction and encapsulation? 

The differences between data abstraction and encapsulation are-

Data abstraction.	Encapsulation.
It solves the problems at the level of design.	Whereas, It solves the problems at the level of execution.
It shows essential aspects while hiding its implementation details.	While it binds code and data into a single unit and hides it from outside access.

Questions and Answers on the Polymorphism in OOPs:

31. Discuss the concept of polymorphism.

It is the ability to exist in multiple states. A single interface can be defined in multiple ways. Such as a ‘house’ class can have a method named ‘clean’ but we cannot define it because different houses have variable levels of cleanliness. Thus, we can define such methods only in subclasses with different definitions for various ‘houses’.

32. What is dynamic polymorphism in OOPs programming?

Dynamic polymorphism, runtime polymorphism, or dynamic binding is a type of polymorphism that occurs during runtime. An example of such polymorphism is the process of method-overriding.

33. Define method-overriding.

Method-overriding is a process in OOPs programming by which the subclass can redefine the methods present in the superclass or base class. Here, the overridden method has the same name and same signature as the original one.

34. Explain static polymorphism in OPPs programming.

Static polymorphism or static binding is a type of polymorphism. It occurs at the time of compilation. An example of compile-time static polymorphism is the process of method-overloading.

35. Define method-overloading.

Method-overloading is a process that allows us to provide the same name to more than one method in a class only if the arguments passed differ from one another.

36. What do you mean by operator-overloading?

Operator-overloading is the process of executing operators using types defined by the users, based on the arguments that are passed along with it.

OOPs Interview Questions and Answers on Methods and Functions:

37. What are the virtual functions in OOPs programming?

Virtual functions are present in the base class. These are the functions that are overridden by the subclass. These are used for achieving dynamic polymorphism.

38. What are the pure virtual functions?

The pure virtual functions are declared only in the parent class. Thus, they don’t possess any definition in the parent class and are to be redefined in the child class.

39. What is a constructor in OOPs?

Constructor is a special method that shares the same name as a class. It is used for creating the objects of that class.

40. What is a destructor in OOPs?

Destructor is a significant method that automatically gets called on when an object is destroyed. This method also recovers the space that was occupied by the destroyed object. It closes the database connections, files, etc. of the destroyed object as well.

41. What are the types of constructors?

The types of constructors differ from language to language. These are-

• Static constructor
• Private constructor
• Default constructor
• Copy constructor
• Parameterized constructor, etc.

42. Define copy constructor.

Copy instructors create an object by copying variables for it from another object in the same class. The concept of copy constructor targets to create new objects from existing ones.

43. What is the use of the ‘finalize’ method in OOPs?

The ‘finalize’ is an object method that is used for freeing up unmanageable resources and cleaning up before the ‘garbage-collection’ method. It assists in memory management tasks as well.

44. What is Garbage Collection(GC) in OOPs programming?

Garbage Collection is an execution of automatic memory management tasks. The Garbage collector frees up the space occupied by destroyed objects.

45. State the difference between a class and a method.

The difference between a class and a method is-

Class	Method
A class is a blueprint that binds the data with its code into a single unit. Classes possess variables, methods, etc.	Whereas, a method is a referable collection of instructions, procedures, or functions that are ought to be performed on provided data.

46. What is a final variable in OOPs?

The final variable is a variable whose value doesn’t change. Hence, It always refers to the same object with non-transversity properties.

Interview Questions and Answers on Handling Exceptions in OOPs programming:

47. What is an exception in OOPs?

The exception is a type of notification that barges into the usual implementation of a program. It gives a pattern to the error and transfers the error to the exception-handler. The exception-handler then resolves the particular error. As soon as an exception is raised, the state of the program gets saved.

48. What is exception-handling in OOPs?

Exception-handling in OOPs is an essential process used for error management. It throws and then catches the errors. Afterward, it executes a centralized mechanism to resolve the caught errors.

49. Differentiate between an error and an exception.

The basic difference between an error and an exception is-

Error.	Exception.
An error is a problem that is not meant to be encountered by the applications.	In contrast, an exception is an order that an application might try to grab.

50. Define a try/ catch block in OOPs?

A try/ catch block in OOPs is used for handling exceptions. The try block is a collection of statements that can lead to an error. Whereas, the catch block snatches the thrown exception.

51. Define the final block in OOPs?

A final block possesses data that implements the essential code like closing a connection. This block works when the try block is working alongside. It also ensures that the block will execute even if some unexpected exception occurs.

Interview Questions and Answers on Limitations of OOPs Programming:

52. Discuss the limitations of OOPs programming.

Though there are an unlimited amount of advantages of using the OOPs programming system, there lie a few disadvantages as well. These are as follows:

• It requires intensive testing from time to time.
• It takes more time to solve the problems.
• Usually, it is not suitable for smaller issues.
• The programmers have to think of solving a problem or an error in terms of objects only.
• Designing any system with it requires proper planning.

Now that we’ve discussed 50+ questions and answers for the OOPs interview, let’s talk about the extent of OOPs usage in today’s digital era.

The extent of OOPs Usage these days:

Different coding/ programming languages used in applications incorporated into your daily life are:

• PHP: to write Facebook, Wikipedia, WordPress, Yahoo, Etsy, etc. blogging web applications.
• C Sharp (C#):  for Windows10, Microsoft office, internet explorer, photoshop, skype, etc.
• Python: for Instagram, Quora, Spotify, Dropbox, Mozzila Firefox, etc.
• Java: used to code Twitter, Spotify (music app), OperaMini, etc.
• C++: programmed YouTube, Windows OS, Amazon.com, Adobe applications, etc.

And so on.

Hence, OOPs technology promises greater programmer productivity, a better quality of software, and lesser maintenance cost. This makes it important for OOPs interview. OOPs systems upgrades easily from small to large systems. This makes the recruiters in the programming industry emphasize more on OPPs knowledge and OPPs-based skills while interviewing the candidates these days. With the increasing importance and scopes of data science and programming, the modern-day OOPs interview questions and answers are getting trickier. To conquer the OOPs interviews in 2022, here we’ve already discussed 50+ model questions and answers for your convenience.

Now, let’s polish up the basic concepts of OOPs quickly. Then we’ll conclude the discussion with the prospects of OOPs interview.

OOPs at a glance to conquer OOPs Interview:

Object-Oriented-Programming or OOPs refers to the languages that use objects for programming. In other words, OOPs is a concept of modern programming language that allows programmers to organize entities and objects. 

Languages:

The most popular Languages for programming are Java, C++, Python, C#, PHP, NET, etc. OOPs languages break the program into smaller bite-sized problems or objects that can be solved efficiently one object at a time. Thus, OOP languages mandatorily require a class for representing the data or object.

OOPs concepts are can be classified as follows: 

1. Class
2. Object
3. Method and Method Passing
4. Pillars of OOPs

• Abstraction
• Encapsulation
• Inheritance
• Polymorphism

1. Compile-time Polymorphism
2. Routine Polymorphism

Now, Let us discuss some of the key components of the OOPs programming system to get a holistic idea of it.

Object:

The object here means any physical or logical entity that has a state or behavior. For example, a paperclip, pencil, chair, laptop, earphones, etc. And the Object-Oriented-Programming is a methodology for designing a program using Objects and Classes. 

Class:

A collection of objects is called a class in OOPs programming system. Class is a logical entity here. In other words, class is the blueprint from which you can create a sole object. However, a class doesn’t consume any space in OOPs programming.

The Four Pillars of OPPs:

Four critical concepts of OOPs are:

1. Abstraction: 

Data Abstraction is the phenomenon where you can abstract important data, hiding away the non-essential data for the users. Therefore, Data Abstraction is the process to identify the essential features of a particular object, disregarding the irrelevant details of the same. 

This is why abstraction is necessary for programming. As the properties and behaviors of similar objects differentiate them from one another, it groups the objects into relevant classes based on their state and behavior.

2. Encapsulation:

Encapsulation is the process of muffling up the data under a solitary unit. This mechanism binds the code and the data it operates together. Therefore, it is like an envelope that protects or prevents the data, so that, any code out of the envelope cannot access it.

3. Inheritance: 

Inheritance is the mechanism in OOPs programming systems by which a particular class is allowed to take up the features (i.e. the methods and the fields) of the other classes. 

4. Polymorphism:

It can be defined as the ability of OOPs languages to distinguish between entities with the same names. It is operated by the signature and declaration of these entities.

That’s all for the OOPs basics. Now, you must be wondering about the prospects you’ll hit after conquering OOPs interview. Here’s how you’ll get your exposure to the programming industry.

Winding up with prospects of OOPs:

Let’s conclude our discussion here with the prospects of the OOPs Interview.

Object-Oriented-Programming targets the implementation of real-world entities such as Inheritance, Hiding, Polymorphism, etc. in programming. However, the main objective of OOPs is to bind the data and the functions that operate on them together. That way, no other part of the code can access this data except its particular function. What happens in the code is primarily executed by the objects in the programming. The users or viewers see the objects while performing tasks you assigned. 

Let’s end this discussion hoping that it’ll prove to be helpful enough for your OOPs interview. Keep polishing your OOPs knowledge and keep practicing the questionnaire we’ve discussed above.

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