Basic OOPs Interview Questions for Freshers

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

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Classes and Objects OOPs Interview Questions

and Answers
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?

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Object Class
A class is basically a template or a
A real-world entity which is an instance
blueprint within which objects can be
of a class
created
An object acts like a variable of the Binds methods and data together into
class a single unit
An object is a physical entity A class is a logical entity
Objects take memory space when they A class does not take memory space
are created when 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

Multiple inheritance comes into picture Multilevel inheritance means a class
when a class inherits more than one inherits from another class which itself
base class is a subclass of some other base class
Example: A class describing a sports
Example: A class defining a child
car will inherit from a base class Car
inherits from two base classes Mother
which inturn inherits another class
and Father
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

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

 Inheritance in Java
 Inheritance in Python

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.

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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.

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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 name
base class with the same parameters/
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 Accessibility from Accessibility from

Name
own 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 implementation
Solves the problem at the design level
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.

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 to
encountered by applications 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