Top 30+ OOPS Interview Questions and Answers

Object-Oriented Programming stands as a fundamental concept in the programming landscape, making it a crucial topic for interviews. To answer every OOPs Interview Questions there needs to be a solid understanding of OOPs. This blog gathers commonly asked OOPs Interview Questions tailored for newcomers, providing valuable insights to help you excel in your Interviews. 

Table of Contents

1) OOPs Interview Questions and answers 

a)  What is meant by the term OOPs? 

b) What is the need for OOPs? 

c) What are some major Object-Oriented Programming languages? 

d) What are some other programming paradigms other than OOPs? 

e) What is meant by Structured Programming? 

f) What are the main features of OOPs? 

g) What are some advantages of using OOPs? 

h) Why is OOPs so popular? 

i) What is an interface? 

j) Can you call the base class method without creating an instance?

2)  Conclusion

OOPs Interview Questions and answers 

Listed below are some of the basic OOPs Interview Questions and answers. 

1) What is meant by the term OOPs? 

OOPs is a coding approach where we structure our programs around "objects." These objects have both data and functions associated with them. The main principles of OOP include  

a) Encapsulation: Keeping data and methods within an object) 

b) Inheritance: Creating new objects based on existing ones) 

c) Polymorphism: Treating objects as instances of their parent class 

OOPs provides a way to organise and manage code more efficiently, making it easier to understand and maintain. It is widely used in the field of software development in the United Kingdom and globally for its modularity and reusability advantages. 
 

  

2) What is the need for OOPs? 

There are numerous reasons why Object-Oriented Programming (OOP) is predominantly favoured, with the most significant being its capacity to facilitate user comprehension of software without knowledge of the specific implementation details. OOP substantially enhances code readability, comprehensibility, and maintainability. Additionally, OOP enables the seamless development and management of extensive software applications. 

3) What are some major Object-Oriented Programming languages? 

Some of the major Object-Oriented Programming languages are listed below: 

a) Java 

b) C++ 

c) Python Object-Oriented Programming  

d) C# 

e) Ruby 

f) Swift 

g) PHP 

h) Kotlin 

i) Objective-C 

j) Smalltalk 

4) What are some other programming paradigms other than OOPs? 

Programming paradigms involve categorising Programming Languages based on their characteristics. The two primary types of programming paradigms are Imperative Programming and Declarative Programming. 

Imperative programming paradigm involves detailing how to execute program logic, defining control flow through statements altering program states. This is subdivided into: 

a) Procedural programming paradigm: This program outlines sequential steps leading to the desired state, typically read sequentially. 

b) Object-Oriented Programming: Programs are structured around objects possessing data and behaviour. 

c) Parallel programming: A paradigm dividing tasks into subtasks and concentrating on their simultaneous execution. 

The Declarative Programming Paradigm focuses on specifying WHAT to execute and outlining program logic without detailed control flow. This paradigm is further divided into: 

a) Logical programming paradigm: Grounded in formal logic, it involves a set of sentences expressing facts and rules to address problems. 

b) Functional programming paradigm: This paradigm constructs programs by applying and combining functions. 

c) Database programming paradigm: Utilised for managing structured data, it organises information into fields, records, and files. 

5) What is meant by structured programming? 

Structured Programming is an approach to programming characterised by a well-organised control flow. The term "structure" here denotes a block containing defined rules and a clear control flow, incorporating elements like (if/then/else), (while and for) loops, block structures, and subroutines. Virtually every programming paradigm, including the OOP model, incorporates the principles of structured programming. 

6) What are the main features of OOPs? 

The main features of OOPs includes the following: 

i) Inheritance 

ii) Encapsulation 

iii) Polymorphism 

iv) Data abstraction 

7) What are some advantages of using OOPs? 

Some of the advantages of using OOPs are given below: 

a) Modularity: OOP promotes modularity by encapsulating data and methods into objects, facilitating easy maintenance and updates. 

b) Reusability: Code reusability is a key advantage, as objects can be reused in different parts of the program or in other projects. 

c) Readability: OOP enhances code readability with a clear structure, making it easier for developers to understand and collaborate. 

d) Scalability: OOP accommodates the growth of software projects, allowing for the creation of large, complex systems with manageable components. 

e) Flexibility: Polymorphism and inheritance provide flexibility, allowing for the creation of versatile and adaptable code. 

f) Data abstraction: OOP hides complex implementation details through data abstraction, exposing only essential features for user interaction. 

g) Code maintenance: OOP simplifies code maintenance by isolating changes to specific objects or classes, reducing the risk of unintended consequences in other parts of the code. 

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8) Why is OOPs so popular? 

The OOPs programming paradigm is regarded as a superior programming style. It facilitates the easier writing of intricate code and ensures straightforward handling and maintenance. The core features of OOPs simplify the resolution of complex scenarios for programmers. Consequently, the popularity of OOPs stems from their ability to enhance code manageability and problem-solving through their foundational principle. 

9) What is an interface? 

An interface in programming is like a contract or a set of rules that a class agrees to follow. It defines a list of methods that a class must have, but it doesn't provide the actual implementation of those methods. Instead, any class that implements the interface must give its own specific code for each method. This promotes a consistent structure and behaviour in diverse classes. 

10) Can you call the base class method without creating an instance? 

No, you cannot call a base class method without creating an instance of the class. The methods of a class, including those in the base class, need an object to be instantiated before they can be invoked. This is because the methods typically operate on the attributes and properties of the specific class instance.  

Attempting to call a method without creating an object would lack the necessary context for the method to execute correctly. Therefore, creating an instance of the class is a prerequisite for invoking any of its methods, including those defined in the base class. 

11) What are the disadvantages of OOPs? 

While OOPs have various advantages, it also has some disadvantages: 

a) Complexity: OOP can introduce complexity, especially in large projects, as it encourages creating multiple classes and intricate relationships between them.  

b) Performance overhead: OOP may have a performance overhead compared to procedural programming, as it involves additional layers of abstraction and indirection.  

c) Learning curve: OOP concepts, such as inheritance and polymorphism, can have a steeper learning curve for beginners, requiring a solid understanding of the principles involved.  

d) Memory overhead: OOP can lead to higher memory consumption due to the storage of additional information related to objects and their relationships.  

e) Not suitable for all types of projects: While OOP is effective for certain scenarios, it may not be the best fit for every type of project, leading to overengineering in simpler applications.  

f) Rigidity: The structure imposed by OOP can sometimes be too rigid, making it challenging to adapt to changing requirements or to extend the functionality without modifying existing code.  

g) Slower execution: In some cases, OOP languages might execute more slowly than languages with a procedural or functional paradigm, impacting performance in certain applications. 

12) What are virtual functions? 

A virtual function is a function declared in a base class that a function with the same signature in a derived class can override. The keyword "virtual" indicates that a function is meant to be overridden in derived classes. When a virtual function is called on a base class reference or pointer, the actual implementation that gets executed is determined by the type of the object it points to or references.    

13) What is the difference between Structured Programming and Object-Oriented Programming? 

14) What is hierarchical inheritance? 

Hierarchical inheritance is a concept in object-oriented programming where a single base class (or parent class) serves as the common ancestor for multiple derived classes (or child classes). In this inheritance structure, each derived class inherits attributes and behaviours from the same parent class, forming a hierarchy.  

The parent class is at the top, and it passes its features to multiple levels of child classes. Each child class can further extend or modify the inherited properties. This hierarchical arrangement allows for the reuse of code and the creation of a clear, structured relationship between classes in the program. 

15) What are the limitations of inheritance? 

The drawbacks of inheritance include heightened execution time and effort due to frequent transitions between classes. Tight coupling between the parent and child classes occurs, necessitating alterations in both when modifying the program. Careful implementation is crucial to prevent incorrect outcomes resulting from the inheritance structure. 

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16) What is a superclass? 

A superclass, in object-oriented programming, is the class from which other classes, called subclasses, inherit properties and behaviours. It is positioned at a higher level in the class hierarchy and serves as a general template. The superclass encapsulates common attributes and methods shared by its subclasses, promoting code reuse. Subclasses inherit these characteristics, allowing developers to create a more organised and modular code structure. 

17) What is a subclass? 

A subclass, in object-oriented programming, is a derived class that inherits attributes and behaviours from a parent class or superclass. It extends the functionality of the parent class, allowing the reuse of code while permitting specific modifications or additions. The subclass retains the features of the superclass and can introduce its own unique characteristics, creating a hierarchical relationship between classes in the program. 

18) What are the different types of inheritance? 

There are several types of inheritance in object-oriented programming:  

a) Single inheritance: A class inherits from only one superclass 

b) Multiple inheritance: A class inherits from more than one superclass, potentially leading to complexities 

c) Multilevel inheritance: A class is derived from another class, and then a new class is derived from it, forming a chain of inheritance 

d) Hierarchical inheritance: Multiple classes inherit from a common base class 

e) Hybrid inheritance: A combination of two or more types of inheritance within a program 

19) What is static polymorphism? 

Static polymorphism, also known as compile-time polymorphism, occurs when the method that needs to be executed is determined at compile time. It is achieved through method overloading, where multiple methods in the same class have the same name but different parameters.  

The appropriate method is chosen by the compiler based on the number and types of arguments provided during the method call. Static polymorphism allows for efficient code compilation and execution, as the decision on which method to call is made at compile time. 

20) What is dynamic polymorphism? 

Dynamic polymorphism, also known as runtime polymorphism, is a concept in OOPs where a function call is resolved at runtime based on the actual type of the object. This is achieved through method overriding, where a subclass provides a specific implementation for a method that is already defined in its superclass. Dynamic polymorphism allows a program to use a common interface for different types of objects, providing flexibility and enabling the selection of the appropriate method implementation at runtime. 

21) What is method overloading? 

Method overloading is a feature in OOPs that allows a class to define multiple methods with the same name but different parameter lists. In other words, within a class, there can be multiple methods sharing the same name but having different types or numbers of parameters. The compiler determines which method to call based on the number or types of arguments provided during the method invocation. Method overloading enhances code readability and provides flexibility in designing classes with multiple functionalities. 

22) Is it always necessary to create objects from class? 

Certainly. If a base class contains non-static methods, the creation of an object is necessary. However, for classes with static methods, object instantiation is not required. In such cases, you can directly invoke static methods using the class name. 

23) What is operator overloading? 

Operator overloading is a concept in object-oriented programming that allows a class to define and use operators (such as +, -, *, /) according to the specific context of that class. In other words, it enables the definition of custom behaviours for standard operators based on the operand's types. This feature provides a way to make user-defined types work with operators in a manner consistent with the class's purpose, enhancing code expressiveness and readability. 

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24) Differentiate between overloading and overriding. 

Overloading refers to the practice of defining multiple methods within the same class, each sharing the same name but having different parameter lists, such as varying types or numbers of parameters. This allows a class to offer multiple functionalities with the same method name, enhancing code flexibility. 

This enables the subclass to offer its own version of the method, modifying or extending the behaviour inherited from the parent class. Overriding is a fundamental feature for achieving polymorphic behaviour, as the decision on which method to execute is made at runtime based on the actual type of the object. 

25) How is data abstraction accomplished? 

Data abstraction in programming is accomplished through the creation of abstract data types and the use of abstract classes and interfaces. Abstract data types allow the definition of data structures along with operations that can be performed on them, hiding the underlying implementation details. Abstract classes and interfaces in object-oriented programming provide a way to declare abstract methods without specifying their implementation. 

26) What is an abstract class? 

An abstract class in object-oriented programming serves as a blueprint for other classes but cannot be instantiated itself. It may contain abstract methods, which are declared but not defined in the abstract class. Subclasses that inherit from the abstract class must provide concrete implementations for these abstract methods. 

27) What is Garbage Collection (GC)? 

Garbage Collection (GC) is an automatic memory management process in programming languages. It involves identifying and reclaiming memory occupied by objects that are no longer in use by the program. Instead of requiring manual memory deallocation, which can lead to memory leaks and bugs, GC tracks and frees up memory occupied by objects that are no longer reachable or referenced in the program. 

28) How is an abstract class different from an interface? 

An abstract class is a class that cannot be instantiated on its own and may contain a mix of abstract (unimplemented) and concrete (implemented) methods. It can have fields (variables) and constructors. Subclasses extend an abstract class, providing concrete implementations for its abstract methods. 

On the other hand, an interface is a collection of abstract methods without any implementation. It cannot have fields or constructors. Classes implement interfaces, agreeing to provide specific functionality for each method declared in the interface. 

29) What are access specifiers and what is their significance? 

Access specifiers, aptly named, are specific keywords used to regulate and define the accessibility of entities such as classes and methods. Examples of access specifiers or access modifiers include "private" and "public." These modifiers are crucial in achieving Encapsulation, a key feature of OOP, as they control the visibility of internal details and contribute to the overall security and organisation of the code. 

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30) What is an exception? 

An exception in programming is an unforeseen or abnormal event that occurs during the execution of a program, disrupting its normal flow. Exceptions can result from various issues, such as erroneous input, system malfunctions, or unexpected conditions. When an exception occurs, it triggers an interruption in the program's execution, and an appropriate exception-handling mechanism is needed to manage and respond to the exceptional situation. 

31) What is meant by exception handling? 

Exception handling is a programming technique aimed at managing and responding to unexpected or exceptional situations that may occur during the execution of a program. When an exceptional event occurs, such as an error or an unexpected condition, the program is interrupted, and control is transferred to a designated block of code known as the "exception handler." 

32) What is a constructor? 

A constructor is a special method in object-oriented programming that is automatically invoked when an object of a class is created. It typically initialises the object's attributes, allocates necessary resources, and prepares the object for use. Constructors have the same name as the class they belong to and may take parameters to customise the initialisation process.  

They play a crucial role in setting up the initial state of objects, ensuring that they are in a valid and usable state as soon as they are instantiated. Constructors are essential for the proper functioning and initialisation of objects in a program. 

33) What is a destructor? 

In Object Oriented Programming, a destructor is a special method that is invoked when an object goes out of scope or is explicitly deleted. Unlike constructors, which are responsible for initialising an object, destructors handle the cleanup tasks before the object is removed from memory.  

Destructors are named with a tilde (~) followed by the class name and do not take any parameters. They are useful for releasing resources, closing files, or performing any necessary cleanup operations to ensure the proper disposal of an object. 

34) What is a copy constructor? 

A copy constructor in OOPs is a special type of constructor that is used to create a new object as a copy of an existing object. It takes an object of the same class as a parameter and creates a new object with the same attributes and values. The purpose of a copy constructor is to provide a convenient way to duplicate an object, ensuring that the new object has the same state as the original. 

Conclusion 

The provided compilation of Top 30+ OOPS Interview Questions and answers aims to equip candidates with a comprehensive understanding of fundamental OOP principles. From encapsulation and inheritance to polymorphism and abstraction, these questions cover key aspects, preparing individuals to demonstrate their proficiency in designing and implementing robust, modular, and maintainable code. 

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