Prime 60+ OOPs Interview Questions in 2023


An object-oriented programming system, or OOPs is a pc programming mannequin that designs or arranges software program for information, or objects, reasonably than capabilities and logic. Oops, have been an essential idea within the realm of programming. In case you have an interview lined up that requires core information of OOPs, then you might be on the proper place. This OOPs interview questions article will assist the totally different questions you may face in an interview. It’ll additionally show you how to land a job in one of many following job roles: C++ Developer, Principal Software program Developer, Python Developer, Golang Engineer, and extra. So, brace your self with an abundance of data coming your means, and ensure to put it to use to create a agency grasp on OOPs fundamentals.

Prime 10 OOPs Interview Questions in 2023

Nice Studying has ready a listing of the highest 10 OOPs interview questions which might be often requested within the interview:

This weblog is additional divided into 3 totally different sections, they’re :

Fundamental OOPs Interview Questions

1. What’s OOPs?

Programmers can use objects to characterize real-world circumstances because of object-oriented programming. Any entity with states and behaviors is an object. Whereas strategies outline an merchandise’s behaviors, states replicate the traits or information of an entity. Objects embrace college students, employees, books, and many others. By exchanging messages, this stuff talk with each other. A category can be a template for constructing an object. A category is required as a way to generate objects. As an illustration, there must be an Worker class as a way to generate an Worker object.

2. Distinction between Procedural programming and OOPs?

Procedural Programming Oops
Procedural Programming relies on capabilities. Object-oriented programming relies on real-world objects.
It exhibits the info to your complete program. It encapsulates the info.
It doesn’t have a scope for code reuse. It gives extra scope for code reuse.
It follows the idea of top-down programming. It follows a bottom-up programming paradigm.
The character of the language is difficult. It’s simpler in nature, so it’s simpler to switch, lengthen and keep.
It’s exhausting to switch, lengthen and keep the code.

3. Why use OOPs?

Programming with OOP allows you to package deal collectively information states and performance to vary these information states whereas maintaining the specifics secret (Take into account the analogy of a automobile, you’ll be able to solely see the steering of the automobile whereas driving, the circuitry behind it’s hidden from you). Consequently, OOP design produces versatile, modular, and summary code. Due to this, it is rather useful for creating bigger applications. Utilizing courses and objects, you could embrace OOP into your code. The objects you assemble may have the states and capabilities of the category to which they belong.

4. What are the essential ideas of OOPs?

The essential ideas of OOPs are:

  • Inheritance
  • Encapsulation
  • Polymorphism
  • Abstraction

5. What’s Encapsulation?

Encapsulation can be part of the OOPs idea. It refers back to the bundling of information with the strategies that function on that information. It additionally helps to limit any direct entry to a few of an object’s elements.

6. What’s Abstraction?

Abstraction is an OOPs idea to construct the construction of real-world objects. It “exhibits” solely important attributes and “hides” pointless info from the skin. The primary focus of abstraction is to cover pointless particulars from the customers. It is without doubt one of the most essential ideas of OOPs.

7. What’s methodology overloading?

There’s a idea the place two or extra strategies can have the identical identify. However they need to have totally different parameters, totally different numbers of parameters, differing kinds, or each. These strategies are often known as overloaded strategies and this characteristic is known as methodology overloading

8. What’s methodology overriding?

Technique overriding is an idea of object-oriented programming.

It’s a language characteristic that enables a subclass or little one class to supply a selected implementation of a methodology which is already offered by one in all its superclasses or guardian courses.

9. Kinds of Inheritance in OOPS

Various kinds of inheritances in OOps are as follows:

  • Single Inheritance
  • A number of Inheritance
  • Multi-level Inheritance
  • Multi-path Inheritance
  • Hierarchical Inheritance
  • Hybrid Inheritance
types of inheritance

10. What are the primary options of OOPs?

The primary options of OOPs are given as follows:

  • In OOP, you mix the code into one unit so you’ll be able to specify the parameters of every piece of information. This technique of wrapping up information right into a single unit is known as encapsulation. 
  • Through the use of courses, you’ll be able to generalise your object varieties and make your software simpler to make use of. That is termed as an abstraction.
  • The power for a category to inherit traits and behaviours from one other class permits for extra code reuse.
  • Polymorphism permits for the creation of a number of objects from a single, adaptable class of code.

11. Is it doable to name the bottom class methodology with out creating an occasion?

Sure, we will presumably name the bottom class methodology with out creating an occasion within the following 3 circumstances:

  1. If the strategy is static
  2. Calling the inherited methodology inside a derived class
  3. Calling the strategy utilizing the bottom key phrase from the sub-classes

The most well-liked case is that of the static strategies.

12. What are the constraints of OOPs?

Following are among the frequent limitations of OOPs:

  • Measurement exceeds that of different applications.
  • It took loads of work to make, and it runs extra slowly than different applications.
  • It’s inappropriate for sure forms of points.
  • It takes some getting used to.

13. What are constructors?

The constructor has the identical identify as the category.
A constructor can be a particular type of methodology. It’s used to initialize objects of the category.

14. Kinds of constructor

Kinds of constructors rely upon languages

  • Non-public Constructor
  • Default Constructor
  • Copy Constructor
  • Static Constructor
  • Parameterized Constructor
Types of constructor

15. What’s the distinction between a category and a construction?

Class: Class is principally a Person-defined blueprint from which objects are created. It consists of strategies ( set of directions) which might be carried out on the objects.

Construction: A construction can be a user-defined assortment of variables. Buildings are additionally totally different information varieties.

A user-defined class serves format or blueprint from which objects may be constructed. In essence, a category is made up of fields often known as attributes and strategies often known as member capabilities that outline actions. A construction is a grouping of variables of varied information varieties beneath one heading.

16. What are the entry modifiers?

Entry modifiers or entry specifiers are the key phrases in object-oriented languages.  It helps to set the accessibility of coursesstrategies, and different members.

17. What languages come beneath the oops idea?

Simula is called the primary object-oriented
programming language, the preferred OOP languages are:

  • Java
  • JavaScript
  • Python
  • C++
  • Visible Fundamental
  • .NET
  • Ruby
  • Scala
  • PHP

Try the OOPs idea in Python Video.

18. What’s inheritance?

Each time one class is derived from one other, it’s known as inheritance. The kid class will inherit all the guardian class’s public and guarded properties and strategies. Aside from the attributes and strategies inherited from the guardian class, it could possibly even have its personal extra set of options. The’ extends’ key phrase is used to specify an inherited class.

Should you derive a  class from one other class that is called inheritance. The kid class will inherit all the general public and guarded properties and strategies from the guardian class. The kid class may also have its personal properties and strategies. An inherited class is outlined through the use of the extends key phrase.

What is inheritance

19. What’s hybrid inheritance?

The kind of inheritance shaped by the mix of several types of inheritances like single, a number of inheritances, and many others. is classed as hybrid inheritance.

20. What’s hierarchical inheritance?

Within the case of a hierarchical inheritance, a number of subclasses inherit from a guardian class. Hierarchical inheritance is a sort of inheritance during which a number of courses are descended from a single guardian or base class. For instance, the fruit class can have ‘apple’, ’mango’, ’banana’, ‘cherry’ and many others. as its subclasses.

21. What are the constraints of inheritance?

It Will increase the execution effort and time. It additionally requires leaping backwards and forwards between totally different courses. The guardian class and the kid class are all the time tightly coupled. Afford modifications in this system would require modifications for the guardian and the kid’s class. Inheritance requires cautious implementation in any other case it could result in incorrect outcomes.

22. What’s a superclass?

A superclass is a category from which a subclass or little one class is derived. Base class and guardian class are different names for a superclass. For instance, if Pupil is a category derived from the Particular person class, then the Particular person class shall be known as the superclass.

A superclass or base class can be a category that works as a guardian to another class/ courses.

For instance, the Automobile class is a superclass of sophistication Bike.

23. What’s a subclass?

A category that derives from one other class is known as a subclass. A subclass inherits the properties of its ancestors or guardian courses. For instance, the category Bike is a subclass or a spinoff of the Automobile class.

24. What’s Polymorphism?

Polymorphism is without doubt one of the most used and core ideas in OOP languages. It explains the idea of various courses can be utilized with the identical interface. Every of those courses can have its personal implementation of the interface. 

25. What’s static polymorphism?

In OOP, static polymorphism determines which methodology to name at compile time. For a similar set off with static polymorphism, the thing may reply in another way. Operate, constructor and operator overloading are examples of static polymorphism.

26. What’s dynamic polymorphism?

Dynamic polymorphism is a technique or course of that handles a name to an overridden methodology throughout runtime reasonably than at compile time. It is usually known as dynamic methodology dispatch or runtime polymorphism. Utilizing methodology overriding, we will create dynamic polymorphism. An instance of runtime polymorphism: is methodology overriding.

27. What’s operator overloading?

The user-defined information sort is given a particular that means by the operator utilizing operator overloading. It’s a compile-time polymorphism.

28. Differentiate between overloading and overriding.

When two or extra strategies in the identical class have the identical identify however totally different parameters, that is known as overloading. The strategy of utilizing the identical methodology signature, i.e., identify and parameters, in each the superclass and the kid class is called overriding.

Differentiate between overloading and overriding

29. What’s encapsulation?

Encapsulation is used to wrap the info and the code which works in a single unit collectively. Instance: Encapsulation permits data-hiding as the info laid out in one class is hidden from different courses.

30. What’s the distinction between public, non-public and guarded entry modifiers?

what is the difference between public, private and protected access modifiers

31. What’s information abstraction?

Knowledge abstraction is without doubt one of the most essential options of OOPs. It solely permits essential info to be displayed. It helps to cover the implementation particulars.

For instance, whereas utilizing a cellular, , how will you message or name somebody however you don’t know the way it really occurs.

That is information abstraction because the implementation particulars are hidden from the consumer.

32. How one can obtain information abstraction?

Knowledge abstraction may be achieved utilizing two methods:

  • Summary class
  • Summary methodology

33. What’s an summary class?

An summary class can be a category which is consists of summary strategies.

So what’s an summary methodology?

These strategies are principally declared however not outlined and If these strategies must be used later in some subclass that point these strategies need to be solely outlined within the subclass.

34. Differentiate between information abstraction and encapsulation.

Differentiate between data abstraction and encapsulation

35. What are digital capabilities?

Digital capabilities are additionally a part of the capabilities that are current within the guardian class and they’re overridden by the subclass. These capabilities assist to attain runtime polymorphism.

36. What’s a destructor?

A destructor is a technique that is known as robotically when an object is destroyed.

The destructor additionally recovers the heap area which was allotted to the destroyed object. It additionally begin closing the recordsdata and database connections of the thing, and many others.

37. What’s a replica constructor?

By copying the members of an present object, the copy constructor initialises the members of a newly shaped object. The argument for the copy constructor is a reference to an object of the identical class. Programmers have the choice of instantly defining the copy constructor. The compiler defines the copy constructor if the programmer doesn’t.

38. What’s using ‘finalize’?

Finalize is used to free the unmanaged assets and likewise assist to wash earlier than Rubbish Assortment(GC). It performs reminiscence administration duties.

39. What’s Rubbish Assortment(GC)?

Programming languages like C# and Java embrace rubbish assortment (GC) as a reminiscence restoration mechanism. A programming language that helps rubbish assortment (GC) incorporates a number of GC engines that robotically launch reminiscence area that has been reserved for issues the applying is now not utilizing.

40. What’s a remaining variable?

A remaining variable can solely obtain one specific initialization. A reference variable that has been marked as remaining is unchangeable in its object reference. The info included within the object, nonetheless, may be modified. Consequently, whereas the thing’s state may be altered, its reference can not.

41. What’s an exception?

An exception is a type of message that interrupts and comes up when there is a matter with the conventional execution of a program. Exceptions present an error and switch it to the exception handler to resolve it. The state of this system is saved as quickly as an exception is raised.

42. What’s exception dealing with?

Exception dealing with in Object-Oriented Programming is an important idea. It’s used to handle errors. An exception handler assist to throw errors after which catch the error as a way to clear up them.

43. What’s the distinction between an error and an exception?

What is the difference between an error and an exception

44. What’s a attempt/ catch block?

The phrases “attempt” and “catch” describe tips on how to deal with exceptions introduced on by coding or information errors whereas a program is working. The part of code the place exceptions happen is known as a attempt block. Exceptions from attempt blocks are caught and dealt with in a catch block.

45. What’s a lastly block?

Lastly designates the part of code that works with the attempt key phrase. It specifies code that’s all the time executed earlier than the strategy is completed, instantly behind the attempt to any catch blocks. No matter whether or not an exception is thrown or caught, the lastly block is all the time executed.

46. Are you able to name the bottom class methodology with out creating an occasion?

Sure, you might be allowed to name the bottom class with out instantiating it however there are some circumstances which might be relevant:

  • If it’s a static methodology
  • The bottom class is inherited by another subclass

47. What’s the distinction between OOP and SOP?

The important thing distinction between structured and object-oriented programming is that the previous permits for the creation of applications utilizing a set of modules or capabilities, while the latter permits for the development of applications utilizing a set of objects and their interactions.

Object-oriented programming entails ideas of objects and courses. All the things is taken into account as an object which has particular properties and behaviours that are represented in a category. Object-oriented programming gives encapsulation and abstraction within the code. Ex: – Java Programming language.

Construction-oriented programming entails the ideas of capabilities and constructions. All the things is taken into account performance and constructions, represented utilizing capabilities—Ex: – C Programming language.

48. What’s the distinction between a category and an object?

Any real-world entity is known as an object. The item has particular properties and behaviours, and the same sort of objects having related options and behaviours are grouped as a category. Therefore, Class is a blueprint of objects, and an object is an occasion of a category.

Ex: -   
1. An Animal is a category, and cat, canine, and many others., are objects with frequent properties like identify, sort, and customary behaviors like talking, strolling, working, and many others. 

2. Cell is a category, and Nokia, moto, iPhone, and many others., are objects with frequent properties like modal_no, coloration, and many others., and customary behaviors like audio_calling, video_calling, music, and many others.

49. What are ‘entry specifiers’?

Entry specifiers are the key phrases in any programming language used to specify the Class’s, methodology’s, interface’s and variable’s behaviour regarding its accessibility. The entry specifiers in C++ Programming are public, non-public, and guarded.

50. Are you able to create an occasion of an summary class?

No, an occasion of the Summary class can’t be created. To implement the summary Class, summary strategies, the Summary Class ought to be prolonged by one other class, and the thing of the implementation class may be created.

OOPs Interview Questions for Skilled

51. What’s an interface?

An interface is a user-defined information sort and is a set of summary strategies. A category implements an interface, thereby inheriting the summary strategies of the interface. A category describes an object’s attributes and behaviours, and an interface incorporates behaviours {that a} class implements. The Class represents “how,” and the interface represents “what’.

52. What are pure digital capabilities?

A pure digital operate/methodology is a operate whose implementations will not be offered within the base class, and solely a declaration is offered. The pure digital operate can have its implementation code within the derived class; in any other case, the derived class may even be thought-about an summary Class. The Class containing pure digital capabilities is summary.

53. Differentiate between a category and a technique.

A category is a blueprint of objects, and it consists of the properties and behavior of the objects.

Strategies are programming constructs that carry out particular duties/behaviour.

54.  Differentiate between an summary class and an interface?

An interface can have solely summary strategies, however an Summary class can have summary and non-abstract strategies.

The interface ought to be used if simply the requirement specification is thought and nothing about implementation. If the implementation is thought, however partially, then an summary class ought to be used. If the implementation is thought utterly, then a concrete Class ought to be used.

55. What are the constraints of OOPs?

  1. Bigger Program dimension – Applications can turn into prolonged if written utilizing OOps ideas in comparison with procedure-oriented programming.
  2. Slower execution – Because the variety of strains of code to be executed is extra comparatively, the execution time can be extra.
  3. Not appropriate for all sorts of Issues.
  4. Testing time can be greater for OOP Options.

56. What are the traits of an summary class?

  1. A category having not less than one pure digital operate is known as an Summary class.
  2. An Summary class can not have objects created, i.e., an summary class can’t be instantiated, however Object references may be created.
  3. An Summary class can have non-abstract capabilities and pure digital capabilities additionally.
  4. The pure digital operate can have its implementation code within the derived class; in any other case, the derived class may even be thought-about an summary Class

57. What’s constructor chaining?

Constructor chaining is a technique to name one constructor from one other regarding a present object reference. It may be completed in two methods: –

  1. Utilizing the “this” key phrase, the reference may be made to the constructor within the present class.
  2. To name the constructor from the bottom class “tremendous” key phrase shall be used.

58. What’s Coupling in OOP, and why is it useful?

The diploma of dependency between the elements is known as coupling.

Kinds of Coupling

A. Tight Coupling – If the dependency between elements is excessive, these elements are referred to as tightly coupled.

Ex: –

Beneath three Lessons are extremely depending on one another therefore they’re tightly coupled.

class P
static int a = Q.j;
class Q
static int j = R.methodology();
class R
public static int methodology(){
return 3;

B.  Free Coupling – If the dependency between elements is low, it’s referred to as unfastened coupling. Free coupling is most popular due to the next causes:-

  1. It will increase the maintainability of code
  2. It gives reusability of code

59. Identify the operators that can not be overloaded

All of the operators besides the + operator can’t be overloaded.

60. What’s Cohesion in OOP?

The modules having well-defined and particular performance are referred to as cohesion.


It improves the maintainability and reusability of code.

 61. What are the degrees of information abstraction?

Highlighting the set of providers by hiding inner implementation particulars is known as abstraction.

Through the use of summary Class and interface, we will implement abstraction

62. What are the forms of variables in OOP?

Variables are primary models to retailer information in RAM for Java applications.

Variables ought to be declared earlier than utilizing them in Java programming. Variable initialization may be static or dynamic. The syntax for variable declaration and static initialization is: –

Kinds of variables

  • Primitive Variables: It’s used to characterize primitive values like int, float, and many others.
  • Reference Variables: It’s used to refer to things in Java.
  • Occasion Variables: Variables whose worth various from object to object are occasion variables. For each object, a separate copy of the occasion variable is created. Occasion variables are declared throughout the Class and out of doors any methodology/block/constructor
  • Static variables: For static Variables, a single copy of the variable is created, and that duplicate is shared between each Class object. The static variable is created throughout class loading and destroyed at class unloading.
  • Static variables may be accessed instantly from the static and occasion space. We aren’t required to carry out initialization explicitly for static variables, and JVM will present default values.
  • Native Variables: Variables declared inside a technique or block or constructor are native variables. Therefore the scope of native variables is identical because the block’s scope during which we declared that variable.

JVM doesn’t present default values, and earlier than utilizing that variable, the initialization ought to be carried out explicitly.

63. What do you perceive by Rubbish Assortment within the OOPs world?

Rubbish assortment is a reminiscence restoration method included in programming languages like C# and Java. A GC-enabled programming language incorporates a number of rubbish collectors that robotically unlock reminiscence area allotted to things which might be now not wanted by this system.

64. Is it doable to run a Java software with out implementing the OOPs idea?

No, since Java programmes are based on the idea of object-oriented programming fashions, or OOPs, a Java software can’t be carried out with out it.

65. What’s the output of the under code?

class Particular person
non-public String present()
return “It is a particular person”;    
class Trainer extends Particular person
protected String present()
return “It is a instructor”;    
public class MathsTeacher extends Particular person
    @Override    public remaining String present()
return “It is a Maths instructor”;    
public static void foremost(String[] identify)
remaining Particular person mt = new MathsTeacher();        
The output shall be: It is a Maths instructor

66. Discover the output of the under code.

class Arithmetic
public remaining double var = 5;
class DeepArith extends Arithmetic
public remaining double var = 10;
public class AdvancedArith extends DeepArith
public remaining double secret = 20;
public static void foremost(String[] num)
Arithmetic arith = new AdvancedArith();        
The right output for this code is 5.

67. Predict the output of the next.

class Guardian
public void show()
class Youngster extends Guardian
{ non-public void show()
{ System.out.println(“Youngster”);
public class foremost
public static void foremost(String args[])
Guardian node = new Youngster(); node.present();
Working this code will generate a compile error as a sub-class operate overriding a brilliant class operate can't be given extra restrictive entry.

68. Implement a Singleton class in Java.

public class Singleton {
    non-public static Singleton occasion;

    non-public Singleton() {
        // Non-public constructor to forestall instantiation.

    public static Singleton getInstance() {
        if (occasion == null) {
            synchronized (Singleton.class) {
                if (occasion == null) {
                    occasion = new Singleton();
        return occasion;

69. Implement a Stack information construction utilizing a LinkedList in Python.

class Node:
    def __init__(self, information=None):
        self.information = information
        self.subsequent = None

class Stack:
    def __init__(self):
        self.head = None

    def is_empty(self):
        return self.head is None

    def push(self, information):
        new_node = Node(information)
        new_node.subsequent = self.head
        self.head = new_node

    def pop(self):
        if self.is_empty():
            elevate Exception("Stack is empty")
        popped_value = self.head.information
        self.head = self.head.subsequent
        return popped_value

70. Implement an summary class in C# with an summary methodology.

summary class Form
    public summary double CalculateArea();

class Circle : Form
    non-public double radius;

    public Circle(double radius)
        this.radius = radius;

    public override double CalculateArea()
        return Math.PI * radius * radius;

Try OOPs in Java Video

Incessantly Requested OOPs Interview Questions

Q: What are the 4 fundamentals of OOP? 

A: OOP stands for Object-Oriented Programming, and its 4 primary ideas are Encapsulation, Abstraction, Polymorphism, and Inheritance. OOP permits programmers to think about software program improvement as if they’re working with precise entities. In OOP, some objects have a subject the place information/information may be saved and may do a number of strategies.

Q: What’s the object-oriented programming interview? 

A: Object-Oriented Programming, additionally often referred to as OOPS, is a type of programming that’s extra object-based and never simply based mostly on capabilities or procedures. Particular person objects are collected into a number of courses. Actual-world entities corresponding to inheritance, polymorphism, and hiding are carried out by OOPS into programming. It additionally permits binding information in addition to code collectively.

Q: What are the three ideas of OOP? 

A: The three foremost ideas of Object-Oriented Programming are Encapsulation, inheritance, and polymorphism.

Q: What’s the idea of OOPS?

A: OOPS or Object-Oriented Programming System is a programming idea that primarily works based mostly on Encapsulation, Abstraction, Polymorphism, and Inheritance. The standard idea of OOPs is to create objects, use them once more all by this system, and eventually manipulate these objects to fetch our outcomes.

Q: Why is OOPS used? 

A: The primary intention of an Object-Oriented Programming System is to implement real-world entities corresponding to polymorphism, inheritance, hiding, and lots of extra in programming. The intention lies in binding collectively the info in addition to capabilities that work on them in order that different elements of the code can not entry the info apart from that operate.

Q: What’s polymorphism in OOPS? 

A: Polymorphism in an Object-Oriented Programming System is a characteristic of object-based programming languages that allow a specific routine to make use of variables of a number of varieties at totally different occasions. It can be referred to as the power of a programming language to current the identical interface for various major information varieties.

Q: Who’s the daddy of OOPS? 

A: The daddy of the Object-Oriented Programming System is taken into account to be Alan Kay by some individuals. He recognized some traits as fundamentals to OOP Kay 1993:1. He coined OOPs round 1966 or 1967 when he was at grad faculty.

Q: What are the primary options of OOPS? 

A: A number of the foremost options in OOPS embrace Lessons, Objects, Knowledge Abstraction, Encapsulation, Inheritance, and Polymorphism. OOP is a programming paradigm that’s based mostly on the thought of objects.

Q: What are the benefits of OOPS?

A: Since OOP is without doubt one of the foremost improvement approaches which is definitely accepted, the benefits are many. A number of the benefits of OOPS embrace Reusability, Knowledge Redundancy, Code Upkeep, Safety, Design Advantages, Straightforward Troubleshooting, Higher Productiveness, Polymorphism Flexibility, and Drawback-solving.

Should you want to be taught extra about such ideas, you’ll be able to be part of a Software program Engineering programs that may show you how to upskill.


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