Must Read 47 OOPs Interview Questions & Answers For Freshers & Experienced [2023]

Attending a programming interview and wondering what are all the OOP interview questions and discussions you will go through? Before attending an interview, it’s better to have an idea of the type of interview questions so that you can mentally prepare answers for them.To help you out, I have created the top OOPs interview question and answers guide to understand the depth and real-intend of OOPs interview questions. The mentioned below list contains some of the frequently asked object-oriented interview questions. It includes both advanced interview questions on OOPs as well, as basic object oriented programming interview questions. Let’s get started.

To begin with, you must engage in understanding the domain well and conduct in-depth studies. Only a solid base will help you sail through such interviews with ease.

OOPs is the programming paradigm based on the concept of objects instead of just functions as procedures. This is a popular methodology used among developers. The top OOP languages are Python, C++, Java, Dart, C#, Go, and Ruby.

What are the main principles of OOPS?

Before delving into the different kinds of advanced oops interview questions and basic OOPS interview questions, let’s clear out a few basic facts about this computer programming model. To put it simply, there are four main principles of OOPs. They are:

• Encapsulation – According to this principle, all the important information is captured inside an object, and only select information is exposed. One of the major benefits of this principle is that it effectively allows greater program security and eliminates the risk of unintended data corruption. 
• Abstraction- The second major principle followed by OOPs is abstraction which states that objects reveal only those internal mechanisms that are necessary to the use of other objects. This helps to steer clear of unnecessary implementation code, which automatically gets hidden under this principle.
• Inheritance- Under this principle, classes can reuse codes from other classes. This leads to a series of advantages like thorough data analysis, reduction in development time, and a higher margin of accuracy. 
• Polymorphism – It enables different types of objects to pass through the same interface. Objects can be designed to share behaviours and they can take on more than one form.

A number of tech giants are looking to hire developers who come with expertise in object-oriented approaches or patterns. Such hiring companies conduct interviews for similar profiles. The main benefit of hiring these candidates is OOP related languages are easier to learn as per the requisites of an organization. This is why prepping for such interviews with the right knowledge of OOPs interview questions and answers will enhance your chances of getting hired by these companies.

The programming world and the languages have come a long way since the inception of programming languages. However, one thing that has stood out the test of time is the Object-Oriented programming concepts. Whether you are looking for a starting a career in programming or trying to improve your skills, you should develop a solid understanding of object-oriented programming or object-oriented programming systems (OOPs).

In this article, we will help you prepare the most crucial OOPs interview questions and answers. Let us review the OOPs concepts and interview questions for freshers around the key features of OOPs, advantages, and limitations. These OOPs interview questions cover the essential aspects of object-oriented programming. Understanding these concepts and the questions that are asked will help you prepare well for a job interview and tackle real-world programming assignments.

Some believe that writing tests under OOP seem harder than otherwise. Moreover,  any refactoring is hard to process. This is like a situation of reusing code wherein, in the words of Erlang, a popular creator, you get a gorilla holding a banana instead of just the latter. In OOP, things come with an inescapable and implicit environment. 

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Top OOPs Interview Questions and Answers

Let’s learn about the most common OOPs concepts in interview questions.

1. What is Object-oriented programming?

This is among the most basic OOPs interview questions or object-oriented programming interview questions. Your answer should be: 

Object-Oriented Programming refers to the programming paradigm defined using objects instead of only functions and methods. The objects contain data, called fields or attributes, and methods that provide the logic or supporting code. It provides capabilities such as inheritance, polymorphism, encapsulation, and abstraction. More simply, this is the approach used in developing applications emphasizing objects. The object is an entity containing data as well as code, which allows the binding of data with code.

Object-oriented programming has various benefits; it is instrumental in breaking down a huge problem into its simple, solvable chunks. For instance, for each mini-problem, the programmers write a class that does what is required.

Advantages of the OOP include-

• Support modularity for troubleshooting-

Whenever there is any problem in a code, there is no need to go through each code in a serial manner. By the look, the programmers can figure out the problem, if it is in any particular class or not. 

This is how amazingly encapsulation works, the objects are self-contained, and each part of the functionality does its own thing, leaving the other bits alone. 

• Code reuse through inheritance

It is useful in creating one generic class and defining subclasses that are supposed to inherit the generic class’ traits. The programmers can also change code in one class, and all the subclasses will inherit the change. 

• Flexibility provided using Polymorphism 

A single object can mould and adapt to whichever class it is in. One function can be created in one parent class. Polymorphism brings flexibility to the design, allowing the same method to have different implementations.

Answering this top pick among OOPs interview questions for freshers is a good approach.

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2. What are the main features of object-oriented programming?

In this OOPs interview question, make sure you list the four main features:

• Inheritance- It enhances the code’s ability to reuse existing objects.
• Encapsulation– Enhances modularity. It makes sure to keep routines separate and avoid any conflict.
• Polymorphism– It allows new shapes to be easily integrated.
• Data Abstraction– It ensures that only essential information is displayed and the details are hidden.

While answering these types of oops interview questions, make sure not to suffice your response by only mentioning the features. Instead, always say at least one line of information of the features.

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3. What are the advantages of Object-oriented programming?

One of the most common oops interview question.

• Problems of any level of complexity can be supported by object-oriented programming.
• Highly complex problems can be handled by object-oriented programming
• It provides an efficient mechanism for code reuse using inheritance which reduces redundancy 
• It provides a mechanism for hiding data
• It is based on a bottom-up approach
• It offers flexibility through polymorphism 
• It improves maintainability of the codeIt is secure and provides security through encapsulation
• It allows for a class-specific behaviour through polymorphism
• It easier to debug
• It is easily maintainable
• It provides for effective troubleshooting

This makes for oops interview questions for experienced and freshers. Questions like such can be asked to any professionals of various experiences. Make sure to prepare well!

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4. What is Structural programming?

Structural programming refers to the traditional method of programming, which is based on functions. The overall program logic is divided into functions to provide a logical structure. It is based on a top-down approach. Structural programming is suitable for easy to moderately complex problems. 

5. What is a class?

A class defines the template or the definition of an object. It is used for creating objects at run time. It provides the data structure, provides initial values for the attributes, and methods that provide the logic for the intended behaviour of the object. The class does not consume memory at runtime. A class refers to a logical entity. E.g., a vehicle may be defined as a class. 

Features of structural programming include-

• It follows a top-down approach.
• The programs are divided into small self-contained structures.
• It focuses on functions and processes that usually work on data.
• It is represented as the logical structure. 
• There is no way of data hiding, and it is less secure. 
• There is the importance given to the code. 
• There is less flexibility.
• There is less abstraction.

This makes for, oops important questions. You may also be asked to enunciate the difference between structured and object-oriented programming. So prepare at least five points for each.

6. What do you mean by an object?

An object refers to the run time instance created from the class during program execution. Objects can refer to real-world entities that have attributes or properties and methods to support the behaviour. Objects consume memory space when they are initialized.

The objects are the first thing the programmers think of frst, while designing. The objects are the class instanecs that allows the programmers to make use of variables and methods from inside the class.

The memory is allocated in the heap memory when the objects are created. The objects are the physical entities that can be manipulated. An object is created by using new keywords. They can also be created using new instance, clone method, and deserialisation. 

There are various uses of objects, they can be used to access a piece of memory using an object reference variable. They can also be used to hold, manipulate  and reference the data. 

This makes for the oops interview questions for experienced professionals. Take this very simple as an opportunity to demonstrate the depth and breadth of your knowledge. An elaborated response as mentioned above, would help in establishing a strong hold in the interview.

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7. Is it always necessary to create objects from class?

No, it is possible to call a base class method if it is defined as a static method.

8. What is a constructor?

A constructor method is used for initializing the objects. They are special types of methods and have the same name as the class. 

A constructor has various advantages attached to it. It is invoked automatically as soon as the object of class is created. This is popularly known as Automatic Initialisation of Objects. The constructor also guarantees that the object undergoes proper initialisaion before being used. 

Look at how the answer has been illustrated mentioning the advantages subtly into the answer. While answering oops interview questions for freshers, you can see this as an opportunity to showcase your technical understanding of the domain to the recruiter.

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9. List the various types of constructors

Multiple types of constructors that are supported across multiple object-oriented programming languages are:

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

10. What is a destructor?

A destructor is a method used for freeing up the resources allocated to an object. This method is automatically invoked when an object is being destroyed. 

The destructor is used to destruct the objects when they are no longer in use. When the object is being destroyed, the destructors are called. Overloading is not allowed, moreover, they indulge in releasing the memory.The destructors can never be static, and they have no return type. 

11. What is meant by a copy constructor?

A copy constructor helps in cloning objects by replicating the values from one object into another object which belongs to the same class. 

It is a special constructor which is used to make a copy of an existence during initialisation. Whenever the object is passed to a function and exact copy (bitwise) of that particular object is created and given to the function. 

OOPs concepts interview questions are asked to understand how well the candidate is thorough with the concepts of the domain. The recruiters typically ask these types of questions to understand how well the candidate can be an asset to the organisation.

12. Can you please highlight the difference between a class and a structure?

A class means a user-defined template from which objects are created at runtime. A class is made up of methods that provide the logic for various behaviours supported by the objects.

A structure means a user-defined combination of attributes of various data types.

Refer to the below-mentioned table to understand the difference-

When you are an experienced person, the recruiter wants to see soem depth in you. In that sense, they can ask you to lat out diffrences among two concepts like shown above. When answering to these types of oops interview questions and answers for experienced professionals, make sure to categorise and structure your response and do not indulge in answering vaguely or without any structure. 

13. Can you please explain the concept of inheritance with an example?

Inheritance is a powerful feature of object-oriented programming which allows classes to inherit properties and methods from other classes. This helps improve code reuse.  

For example, a base class represents a logical concept, such as a vehicle that may define only the common properties shared by all types of vehicles. However, child classes can inherit from this base class to define more specific types of classes such as a truck, a car, or a bus. In this case, the child classes will inherit the common attributes of the vehicle, and will be able to define attributes, method specific to its own. 

14. What are the limitations of inheritance?

The inheritance requires more processing time for the programs as it has to navigate various classes during execution. Due to inheritance, the parent and child class are tightly coupled. When any changes are needed in the logic, it may require changes in both parent and child classes. 

If the inheritance is not correctly implemented, it can lead to undesired results. 

15. What are the various types of inheritance?

• Single 
• Multiple 
• Multi-level 
• Hierarchical 
• Hybrid 

16. What is the meaning of hierarchical inheritance?

When multiple subclasses inherit a base class, it is called hierarchical inheritance. 

The derived class can act as a base class to new derived class. The more higher in hierarchy the class would be, more general information it would contain.

17. Distinguish between multiple and multi-level inheritances? 

In the case of the multiple inheritance, a class inherits more than one parent class. In contrast, multi-level inheritance means that class inherits from another class, which is a subclass of some other parent class.

Refer to the below-menitoned table to understand the differences-

This question can form tricky OOPs interview questions asked during the interview. Make sure to not get confused to somewhat similar names. You may use the aboev table as a cheat sheet for yourself.

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18. How do you define hybrid inheritance?

The hybrid inheritance is defined as the usage of multiple and multilevel inheritance in a single class.

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19. What is a subclass?

The child class which inherits from another class is referred to as the subclass. 

20. Define a superclass? 

A superclass implies a class from which other classes inherit. e.g., the vehicle will be referred to as superclass of classes car, bus, or truck if they all inherited from the same superclass. 

21. What is meant by an interface?

An interface allows a declaration of methods without providing a definition. 

You cannot create objects from the interface. When a class implements an interface, it needs to implement the methods provided by the interface. 

With the interface implementation, a class can perform a role that is different from its class hierarchy. It also provides a standard set of methods for a group of classes. The objects in these classes can be accessed using standard set of methods without concerning the location in class hierarchy.

An interface is of high importance to achieve abstraction. Functionality of multiple inheritance can be supported. Moreover, it is possible to attain lose coupling using interface. OOPs coding interview questions  like this should be elaborated and must make a mention of some importance the function performs.

22. What is polymorphism?

Polymorphism is a significant feature of object-oriented programming. It means an ability to exist in multiple forms. A single interface can be implemented in multiple ways by providing various definitions. 

Features of Polymorphism-

• Functionality of a method behaves differently in different scenarios.
• The method behaviour depends upon the provided data.
• Same name for a member or a method can exist in a class with different types.
• It supports implicit type conversion.

Types of Polymorphism-

• Run-Time
• Compile-Time

Advantages of Polymorphism-

• Codes can be reused using polymorphism.
• Coupling reduction between functionalities.
• Single variable name can be supported for multiple data types.
• Reduction in complexity.
• Better maintainability. 

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23. What is meant by static polymorphism?

The static polymorphism or static binding allows us to link a function with objects during compilation. It can be implemented by method overloading of operator overloading. 

Features of static polymorphism-

• Collects information during compie-time to call a method.
• It occurs at compile- time.
• Alternatively called as static binding and early binding.
• Method overloading is an example of static polymorphism.

24. What is meant by dynamic polymorphism?

A dynamic polymorphism or dynamic binding allows for a call to an overridden method at the run time. 

Features of dynamic polymorphism-

• Collects information at run-time to call a method.
• Occurs at run-time.
• Alternatively called as dynamic binding or late binding.
• The execution speed is slow.
• Method overriding is an example of dynamic polymorphism.

25. What is method overloading?

One of the most common oops interview question. The method overloading is a very useful feature of object-oriented programming in which multiple methods can have the same method name; however, they have different arguments. The call to the method is resolved based on the arguments.

Advantages of method overloading-

• Allows to use the same name for a group of methods having the same purpose.
• Provides an easy way t handle the default parametre value.
• It is possible only in same class.
• It is used to implement the compile-time polymorphism.
• Static methods  can be overloaded.
• It is helpful to extend functionalities.

26. What is the meaning of method overriding?

Method overriding allows the child class to redefine methods of parent class by applying its implementations. However, the method name, arguments, and return types remain the same. 

27. Can you explain what operator overloading is?

The term operator overloading means that depending on the arguments passed, the operators’ behaviour can be changed. However, it works only for user-defined types. 

Advantages of method overriding-

• Only possible in derived classes.
• The method must be a non-virtual or static method for overriding t to happen.
• It is helpful to overwrite or change the functionalities.
• It is used to implement the run-time polymorphism.

28. How do you explain the difference between overloading and overriding?

Overloading a method means that multiple methods share the same method name but have different arguments. However, in the case of the overriding, the child class can redefine the implementation of a method by retaining the same arguments. Another difference is that the overloading is resolved at compile-time while overriding is resolved at run time.

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29. What do you know about encapsulation?

One of the most common OOPs interview question. Encapsulation is an important feature of object-oriented programming. It allows the binding of the data and the logic together in a single entity. It also allows the hiding of data. 

Advantages of using encapsulation-

• It provides better control over the data.
• A field of class can be made read-only or write-only.
• It provides higher flexibility.
• There is more scope for easy debugging and testing.
• The data can be hidden using encapsulation, thus increasing security.

30. What is meant by data abstraction?

Data abstraction refers to the ability of object-oriented programming that allows hiding the implementation details of logic yet allows for access to only important information.

Advantages of data abstraction-

• Focus on the observable behaviour of an object.
• Problems can be solved at the design level using abstraction.
• Unwanted information can be hidden using data abstraction.
• Reliability can come into implementation with data-hiding features. 
• It can be used by either using an abstract class or interface.

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31. How can data abstraction be accomplished?

Data abstraction can be accomplished through either an abstract class or an abstract method. 

32. What is meant by abstract class?

Any OOPS Interview Question and Answers guide won’t be complete without this question. An abstract class is made of abstract methods. The abstract methods are only declared, however, not implemented. When a subclass needs to use the methods, it needs to implement those methods. 

Features of abstract class-

• It does not support multiple inheritances.
• It contains data members.
• It consists of constructors.
• It can possess access modifiers for the subs, functions, and properties.
• Only the complete member of the abstract class can be static.

33. Can you please elaborate on ‘access specifiers’?

Support this OOPs interview question’s answer with examples:

Access specifiers are special keywords that control the accessibility of methods or classes etc. They are also called access modifiers and are used to achieve encapsulation. e.g., the keywords public, private, and protected are some examples of access specifiers. 

34. How do you create an instance of an abstract class?

You cannot create an instance of an abstract class since it lacks implementation logic in its methods. You first need to create a subclass that implements all the methods before an object can be initialized. 

35. What is a virtual function?

A virtual function is defined in the parent class and may have definitions implemented. A subclass can override these definitions. 

36. What is a pure virtual function?

A pure virtual function is only declared in the parent class. It is also referred to as an abstract function. Pure virtual functions do not contain any definition in the base class. They must be redefined in the subclass for the implementation needed. 

37. Distinguish between data abstraction and encapsulation.

Data abstraction is the ability to hide unwanted information. 

The encapsulation refers to the ability to hide the data as well as the method together.

Refer to the below-mentioned table to understand the differences between the two-

38. What are the differences between interfaces and abstract classes?

It is one of the general oops interview questions and answers guides. An abstract class can support both abstract and non-abstract methods. However, the interface allows only abstract methods. 

In the case of an abstract class, both final and non-final variables are supported. However, the interface has variables that are, by default, defined as final. 

The abstract class can have private, and public attributes, but interfaces have attributes as public by default. 

Refer to the below-mentioned table to understand the differences between the two-

This can be OOPs tricky interview questions, where the interview is not asking to list the differences between generic functions but rather is pitting two different tasks together. 

39. What is a final variable?

A final variable means a variable whose value doesn’t change.

40. What is meant by an exception?

An exception is an event raised during a program execution caused by undesirable input or a condition that prevents further processing. An exception causes an interruption in the program’s normal execution and must be handled via exception handling logic to avoid the program’s termination. 

A run-time error in the program causes it. It is an event that occurs during the execution of a program. It is identified as an event which disrupts the normal operation/ flow of the program’s instructions.

There are various advantages attached to the exception-handling, such as maintaining the proper and normal flow of the program. It does so by separating the error-prone code from the normal code. Moreover, clarifying the code and removing any errors increases the readability of the code altogether.

41. Define exception handling

Exception handling refers to the mechanism used for handling the exceptions raised during program execution. It allows for the graceful handling of undesirable results.

42. Is an error basically the same as an exception?

An error means a problem that the program should not catch while the exception implies a condition that should be caught by the program.

43. What is a try-catch block?

A try-catch block is used for exception handling. The set of statements that may cause a potential error is enclosed in a try block. When an exception is raised, it is caught by the catch block. The logic to handle an exception is placed inside the catch block.

44. What is a finally block?

A ‘finally’ block is used for executing essential statements such as to free the memory, close files, or database connections, even if an exception occurs. The finally block always runs. 

Features of a finally block-

• It is used to execute an important code.
• It is always executed whether the exception is handled or not.
• It should be the last block of execution.
• It contains all the important and crucial statements, whether the exception happens or not. 

45. What is the method ‘finalize’ used for?

The finalize method is called to free the unused resources before the garbage collector gets initiated. 

46. What is Garbage Collection, and how does it work?

Garbage collection is the ability of the programming language to perform automatic memory management. It automatically frees up the memory by removing the objects that are no longer required.

47. Should you always use Object-oriented programming? Are there any limitations of Object-oriented programming?

This is one of the advanced OOPs interview questions and answers. Though object-oriented programming offers many advantages, it has some disadvantages too.  Know this when preparing for answers for  OOPs concepts interview questions for freshers. First of all, it has a steep learning curve compared to procedural programming. It may take a while to get used to thinking and programming in terms of objects for many people. Secondly, it may take more experience to design a program in terms of objects. Using OOPs concepts for smaller programming tasks may not be efficient.

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These are some of the basic OOPS interview questions. If you still need more practice, check out these advanced object oriented interview questions that are mentioned in the list below.

Top Advanced OOPs Interview Questions

Here are some of the most advanced oop interview questions that you should prepare before your interview. These object oriented interview questions will keep you prepared for all types of curveballs from the recruiters. 

1. What is the meaning of Constructor? Can you state some of the main features of Constructor?

Ans: This is one of the most frequently asked object oriented programming interview questions. The constructor can be defined as a special method of a class that can be called automatically when the instance of a class is created. Some of the main features of a Constructor include

• It does not have any return type
• It can be overloaded
• It can be invoked automatically by.NET framework, thus eliminating the need to declare a constructor.

2. Can you state any one way of preventing a class from overriding in C#?

Ans: We can prevent a class from overriding in C# quite easily with the help of a sealed keyboard. 

3. When is it recommended to use a structure instead of a class?

Ans: This is one of the frequently asked  interview questions on OOPs . Here’s how you can answer it.

You should not define a structure unless the specific type has all these characteristics

• The instance size is smaller than 16 bytes. 
• It is immutable.
• It should not have to be boxed frequently and 
• It can logically represent a single value.

4. Why is the virtual keyword used in code?

Ans: Virtual keyword is especially useful while defining a class since it can specify that the methods and properties of the said class can be overridden in derived classes.

Conclusion

 We hope our Google Analytics Questions and Answers guide for OOP interview questions is helpful. We will be updating the guide regularly to keep you updated. Object-oriented programming takes some time to master. We recommend that you practice a lot to get the fundamentals clear, which will help you answer the questions during an interview. We hope our Google Analytics Questions and Answers guide is helpful. We will be updating more OOPs concept interview questions. 

Object-oriented programming interview questions help prepare you well for the related interviews.

The Popularity Of OOPs

OOPs programming paradigm is thought of as a much better style for programming. It lets developers write code much easier, while also allowing users code handling and maintenance on an easy scale. Programmers get to sort out scenarios that are complex easily based on the OOP structure – Data Abstraction, Data Encapsulation, Data Inheritance, and Polymorphism, contributing to the overall popularity of OOPs.

We would like to conclude with one trick to help you practice the concept in real life and face OOPs interview questions for freshers.

Whenever you are looking at real-world objects, try to relate them to Object-oriented concepts, and try to identify their attributes, methods. Once you get the hang of this, programming will become much easier and enjoyable.

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