Object-Oriented Programming is one of the main concepts in the programming

world, therefore, every interview that you attend requires knowledge of OOPs. This
article compiles the most frequently asked OOPs Interview Questions for freshers
which will help you ace your interviews. So go ahead and get prepared.

Let’s take a quick look at all the topics of discussion:

 Basic OOPs Interview Questions

 OOPs Interview Questions Classes and Objects
 Interview Questions on Features of OOPs
o Inheritance 
o Polymorphism
o Encapsulation
o Data abstraction
 Methods and functions Interview Questions
 Exception handling Interview Questions
 Limitations of OOPs

OOPs Interview Questions

1. What is the difference between OOP and SOP?
2. What is OOPs?
3. Why use OOPs?
4. What are the main features of OOPs?
5. What is an object?
6. What is a class?
7. What is the difference between a class and a structure?
8. Can you call the base class method without creating an instance?
9. What is the difference between a class and an object?
10. What is inheritance?

Basic OOPs Interview Questions

1. What is the difference between OOP and SOP?

Object-Oriented Programming Structural Programming

Object-Oriented Programming is a type
of programming which is based on Provides logical structure to a program
objects rather than just functions and where programs are divided functions
procedures
Bottom-up approach Top-down approach
Provides data hiding Does not provide data hiding
Can solve problems of any complexity Can solve moderate problems
Code can be reused thereby reducing
Does not support code reusability
redundancy
2. What is Object Oriented Programming?

Object-Oriented Programming(OOPs) is a type of programming that is based on

objects rather than just functions and procedures. Individual objects are grouped into
classes. OOPs implements real-world entities like inheritance, polymorphism, hiding,
etc into programming. It also allows binding data and code together.

3. Why use OOPs?

 OOPs allows clarity in programming thereby allowing simplicity in solving

complex problems
 Code can be reused through inheritance thereby reducing redundancy
 Data and code are bound together by encapsulation
 OOPs allows data hiding, therefore, private data is kept confidential
 Problems can be divided into different parts making it simple to solve
 The concept of polymorphism gives flexibility to the program by allowing the
entities to have multiple forms

4. What are the main features of OOPs?

 Inheritance
 Encapsulation
 Polymorphism
 Data Abstraction

Classes and Objects OOPs Interview Questions

5. What is an object?

An object is a real-world entity which is the basic unit of OOPs for example chair, cat,
dog, etc. Different objects have different states or attributes, and behaviors.

6. What is a class?

A class is a prototype that consists of objects in different states and with different
behaviors. It has a number of methods that are common the objects present within
that class.

7. What is the difference between a class and a structure?

Class: User-defined blueprint from which objects are created. It consists of methods

or set of instructions that are to be performed on the objects.

Structure: A structure is basically a user-defined collection of variables which are of

different data types.
8. Can you call the base class method without creating an instance?

Yes, you can call the base class without instantiating it if:

 It is a static method
 The base class is inherited by some other subclass

9. What is the difference between a class and an object?

Object Class

A real-world entity which is an instance of a A class is basically a template or a blueprint

class within which objects can be created

Binds methods and data together into a

An object acts like a variable of the class
single unit

An object is a physical entity A class is a logical entity

Objects take memory space when they are A class does not take memory space when
created created

Objects can be declared as and when

Classes are declared just once
required

To know more about objects and classes in JAVA, Python, and C++ you can go
through the following blogs:

 Objects in Java
 Class in Java
 Objects and classes in Python
 Objects in C++

OOPs Interview Questions – Inheritance

10. What is inheritance?
Inheritance is a feature of OOPs which allows classes inherit common properties
from other classes. For example, if there is a class such as ‘vehicle’, other classes
like ‘car’, ‘bike’, etc can inherit common properties from the vehicle class. This
property helps you get rid of redundant code thereby reducing the overall size of the
code.

11. What are the different types of inheritance?

 Single inheritance
 Multiple inheritance
 Multilevel inheritance
 Hierarchical inheritance
 Hybrid inheritance
12. What is the difference between multiple and multilevel inheritance?
Multiple Inheritance Multilevel Inheritance

Multilevel inheritance means a class inherits

Multiple inheritance comes into picture when
from another class which itself is a subclass
a class inherits more than one base class
of some other base class

Example: A class describing a sports car will

Example: A class defining a child inherits
inherit from a base class Car which inturn
from two base classes Mother and Father
inherits another class Vehicle

13. What is hybrid inheritance?

Hybrid inheritance is a combination of multiple and multi-level inheritance.

14. What is hierarchical inheritance?

Hierarchical inheritance refers to inheritance where one base class has more than
one subclasses. For example, the vehicle class can have ‘car’, ‘bike’, etc as its
subclasses.

15. What are the limitations of inheritance?

 Increases the time and effort required to execute a program as it requires jumping
back and forth between different classes
 The parent class and the child class get tightly coupled
 Any modifications to the program would require changes both in the parent as well as
the child class
 Needs careful implementation else would lead to incorrect results

16. What is a superclass?

A superclass or base class is a class that acts as a parent to some other class or
classes. For example, the Vehicle class is a superclass of class Car.

17. What is a subclass?

A class that inherits from another class is called the subclass. For example, the class
Car is a subclass or a derived of Vehicle class.

OOPs Interview Questions – Polymorphism

18. What is polymorphism?

Polymorphism refers to the ability to exist in multiple forms. Multiple definitions can
be given to a single interface. For example, if you have a class named Vehicle, it can
have a method named speed but you cannot define it because different vehicles
have different speed. This method will be defined in the subclasses with different
definitions for different vehicles.

19. What is static polymorphism?

Static polymorphism (static binding) is a kind of polymorphism that occurs at compile
time. An example of compile-time polymorphism is method overloading.
20. What is dynamic polymorphism?
Runtime polymorphism or dynamic polymorphism (dynamic binding) is a type of
polymorphism which is resolved during runtime. An example of runtime
polymorphism is method overriding.

21. What is method overloading?

Method overloading is a feature of OOPs which makes it possible to give the same
name to more than one methods within a class if the arguments passed differ.

22. What is method overriding?

Method overriding is a feature of OOPs by which the child class or the subclass can
redefine methods present in the base class or parent class. Here, the method that is
overridden has the same name as well as the signature meaning the arguments
passed and the return type.

23. What is operator overloading?

Operator overloading refers to implementing operators using user-defined types
based on the arguments passed along with it.

24. Differentiate between overloading and overriding.

Overloading Overriding

Child class redefining methods present in the

Two or more methods having the same
base class with the same parameters/
name but different parameters or signature
signature

Resolved during compile-time Resolved during runtime

To know more about polymorphism in Java and Python, read the below articles:

 Polymorphism in Java
 Polymorphism in Python

OOPs Interview Questions – Encapsulation

25. What is encapsulation?
Encapsulation refers to binding the data and the code that works on that together in
a single unit. For example, a class. Encapsulation also allows data-hiding as the data
specified in one class is hidden from other classes.

26. What are ‘access specifiers’?

Access specifiers or access modifiers are keywords that determine the accessibility
of methods, classes, etc in OOPs. These access specifiers allow the implementation
of encapsulation. The most common access specifiers are public, private and
protected. However, there are a few more which are specific to the programming
languages.

27. What is the difference between public, private and protected access modifiers?
 
 Accessibility from own Accessibility from Accessibility from
Name
class derived class world

Public Yes Yes Yes

Private Yes No No
Protected Yes Yes No
To know more about encapsulation read along:

 Encapsulation in Java
 Encapsulation in C++
 Encapsulation in Python

Data abstraction

28. What is data abstraction?

Data abstraction is a very important feature of OOPs that allows displaying only the
important information and hiding the implementation details. For example, while
riding a bike, you know that if you raise the accelerator, the speed will increase, but
you don’t know how it actually happens. This is data abstraction as the
implementation details are hidden from the rider.

29. How to achieve data abstraction?

Data abstraction can be achieved through:

 Abstract class
 Abstract method

30. What is an abstract class?

An abstract class is a class that consists of abstract methods. These methods are
basically declared but not defined. If these methods are to be used in some
subclass, they need to be exclusively defined in the subclass.

31. Can you create an instance of an abstract class?

No. Instances of an abstract class cannot be created because it does not have a
complete implementation. However, instances of subclass inheriting the abstract
class can be created.

32. What is an interface?

It is a concept of OOPs that allows you to declare methods without defining them.
Interfaces, unlike classes, are not blueprints because they do not contain detailed
instructions or actions to be performed. Any class that implements an interface
defines the methods of the interface.

33. Differentiate between data abstraction and encapsulation.

 

Data abstraction Encapsulation

Solves the problem at the design level Solves the problem at the implementation
 level

Allows showing important aspects while Binds code and data together into a single
hiding implementation details unit and hides it from the world

To know more about data abstraction, below articles might help you:

 Abstraction in Java
 Abstraction in Python

Methods and Functions OOPs interview questions

34. What are virtual functions?

Virtual functions are functions that are present in the parent class and are overridden
by the subclass. These functions are used to achieve runtime polymorphism.

35. What are pure virtual functions?

Pure virtual functions or abstract functions are functions that are only declared in the
base class. This means that they do not contain any definition in the base class and
need to be redefined in the subclass.

36. What is a constructor?

A constructor is a special type of method that has the same name as the class and is
used to initialize objects of that class.

37. What is a destructor?

A destructor is a method that is automatically invoked when an object is destroyed.
The destructor also recovers the heap space that was allocated to the destroyed
object, closes the files and database connections of the object, etc.

38. Types of constructors

Types of constructors differ from language to language. However, all the possible
constructors are:

 Default constructor
 Parameterized constructor
 Copy constructor
 Static constructor
 Private constructor

39. What is a copy constructor?

A copy constructor creates objects by copying variables from another object of the
same class. The main aim of a copy constructor is to create a new object from an
existing one.

40. What is the use of ‘finalize’?

Finalize as an object method used to free up unmanaged resources and cleanup
before Garbage Collection(GC). It performs memory management tasks.
41. What is Garbage Collection(GC)?
GC is an implementation of automatic memory management. The Garbage collector
frees up space occupied by objects that are no longer in existence.

42. Differentiate between a class and a method.

Class Method

A class is basically a template that binds the Callable set of instructions also called a
code and data together into a single unit. procedure or function that are to be
Classes consist of methods, variables, etc performed on the given data

43. Differentiate between an abstract class and an interface?

 

Basis for comparison Abstract Class Interface

Can have abstract as well as

Methods Only abstract methods
other methods

May contain final and non- Variables declared are final

Final Variables final variables by default

Accessibility of Data Can be private, public, etc Public by default

Members
Can provide the Cannot provide the
Implementation implementation of an implementation of an abstract
interface class

44. What is a final variable?

A variable whose value does not change. It always refers to the same object by the
property of non-transversity.

OOPs Interview Questions – Exception Handling

45. What is an exception?

An exception is a kind of notification that interrupts the normal execution of a

program. Exceptions provide a pattern to the error and transfer the error to the
exception handler to resolve it. The state of the program is saved as soon as an
exception is raised.

46. What is exception handling?

Exception handling in Object-Oriented Programming is a very important concept that

is used to manage errors. An exception handler allows errors to be thrown and
caught and implements a centralized mechanism to resolve them.
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47. What is the difference between an error and an exception?

Error Exception
Errors are problems that should not be Conditions that an application might try
encountered by applications to catch
48. What is a try/ catch block?

A try/ catch block is used to handle exceptions. The try block defines a set of
statements that may lead to an error. The catch block basically catches the
exception.

49. What is a finally block?

A finally block consists of code that is used to execute important code such as
closing a connection, etc. This block executes when the try block exits. It also makes
sure that finally block executes even in case some unexpected exception is
encountered.

OOPs Interview Questions – Limitations of OOPs

50. What are the limitations of OOPs?

 Usually not suitable for small problems

 Requires intensive testing
 Takes more time to solve the problem
 Requires proper planning
 The programmer should think of solving a problem in terms of objects