Top 50 OOP Interview Questions and Answers

In this article, we’ll see OOP Interview Questions and Answers.

Object-Oriented Programming (OOP) is a fundamental paradigm in software development, and its concepts play a crucial role in modern programming languages. If you’re preparing for a job interview in the software development field, it’s essential to be well-versed in OOP principles and practices. In this blog post, we’ll explore some of the top OOP interview questions you might encounter and provide comprehensive answers to help you ace your oop interview questions.

OOP Interview Questions and Answers

see below for a list of OOP interview questions with answers

What Is Object-Oriented Programming?

Object-Oriented Programming (OOP) is a programming paradigm where the complete software operates as a bunch of objects talking to each other. An object is a collection of data and methods that operate on its data.

Why OOP?

The main advantage of OOP is better manageable code that covers the following.

1) The overall understanding of the software is increased as the distance between the language spoken by developers and that spoken by users.

2) Object orientation eases maintenance by the use of encapsulation. One can easily change the underlying representation by keeping the methods the same.

OOP paradigm is mainly useful for relatively big software. See this for a complete example that shows the advantages of OOP over procedural programming.

What are the various elements of OOP?

Various elements of OOP are:

– Object
– Class
– Method
– Encapsulation
– Information Hiding
– Inheritance
– Polymorphism

What is Abstraction?

Abstraction is an OOPS concept to construct the structure of real-world objects. During this construction, only the general states and behaviors are taken and more specific states and behaviors are left aside for the implementers.

What is Encapsulation?

Encapsulation is an OOPS concept to create and define the permissions and restrictions of an object and its member variables and methods. A very simple example to explain the concept is to make the member variables of a class private and provide public getter and setter methods. Java provides four types of access level modifiers: public, protected, no modifier, and private.

What is the difference between Abstraction and Encapsulation?

“Program to interfaces, not implementations” is the principle for Abstraction, and “Encapsulate what varies” is the OO principle for Encapsulation.
Abstraction provides a general structure of a class and leaves the details for the implementers. Encapsulation is to create and define the permissions and restrictions of an object and its member variables and methods.
Abstraction is implemented in Java using the interface and abstract class while Encapsulation is implemented using four types of access level modifiers: public, protected, no modifier, and private.

What is Polymorphism?

Polymorphism is the occurrence of something in various forms. Java supports various forms of polymorphism like polymorphic reference variables, polymorphic methods, polymorphic return types, and polymorphic argument types.
What is Inheritance?

A subclass that can inherit the states and behaviors of its superclass is known as inheritance.

What is multiple Inheritance?

A child class inheriting states and behaviors from multiple parent classes is known as multiple Inheritance.
What is the diamond problem in inheritance?

In the case of multiple Inheritance, suppose class A has two subclasses B and C, and class D has two superclasses B and C.If a method present in A is overridden by both B and C but not by D then from which class D will inherit that method B or C? This problem is known as a diamond problem.

Why Java does not support multiple Inheritance?

Java was designed to be a simple language and multiple Inheritance introduces complexities like a diamond problem. Inheriting states or behaviors from two different types of classes is a case that in reality very rare and it can be achieved easily through an object association.

What are Static Binding and Dynamic Binding?

Static or early binding is resolved at compile time. Method overloading is an example of static binding.

Dynamic or late or virtual binding is resolved at run time. Method overriding is an example of dynamic binding.

What is the meaning of the “IS-A” and “HAS-A” relationship?

“IS-A” relationship implies inheritance. A sub-class object is said to have an “IS-A” relationship with the superclass or interface. If class A extends B then A “IS-A” B. It is transitive, that is, if class A extends B and class B extends C then A “IS-A” C. The “instanceof” operator in java determines the “IS-A” relationship.

When class A has a member reference variable of type B then A “HAS-A” B. It is also known as Aggregation.

What is Association?

Association is a relationship between two objects with multiplicity.

What is Aggregation?

Aggregation is also known as the “HAS-A” relationship. When class Car has a member reference variable of type Wheel then the relationship between the classes Car and Wheel is known as Aggregation. Aggregation can be understood as a “whole to its parts” relationship.

The car is the whole and the Wheel is part. The wheel can exist without the Car. Aggregation is a weak association.

What is Composition?

A composition is a special form of Aggregation where the part cannot exist without the whole. Composition is a strong Association. The composition relationship is represented as aggregation with one difference that the diamond shape is filled.

What is Dependency?

When one class depends on another because it uses that at some point in time then this relationship is known as Dependency. One class depends on another if the independent class is a parameter variable or local variable of a method of the dependent class. A Dependency is drawn as a dotted line from the dependent class to the independent class with an open arrowhead pointing to the independent class.

What is the difference between Association and Dependency?

The main difference between Association and Dependency is in the case of Association one class has an attribute or member variable of the other class type but in the case of Dependency a method takes an argument of the other class type or a method has a local variable of the other class type.

What is a Class?

A class is the specification or template of an object.

What is an Object?

The object is an instance of the class.

What are the advantages of OOPS concepts?

Major advantages of OOPS programming are;

Simplicity: OOPS programming objects model real-world objects, so the complexity is reduced and the program structure is clear.
Modularity: Each object forms a separate entity whose internal workings are decoupled from other parts of the system.
Modifiability: It is easy to make minor changes in the data representation or the procedures in an OO program. Changes inside a class do not affect any other part of a program, since the only public interface that the external world has to a class is through the use of methods.
Extensibility: adding new features or responding to changing operating environments can be solved by introducing a few new objects and modifying some existing ones.
Maintainability: Objects can be maintained separately, making locating and fixing problems easier.
Reusability: Objects can be reused in different programs.

What are the fundamental concepts of object-oriented technology? Explain them.

Class – A class is a collection of data and operations on data. Data and operations/functions/methods are placed together in a single unit, i.e., class. This feature is known as encapsulation.

Objects – A class is like a blueprint of a building. An object is the building itself. Technically speaking, an object is the real entity of a specific class, which involves the real operations of an OOP application.

Inheritance: The properties of one class can be used by another class in the best way, and the class can be extended as the need may be. This feature is known as Inheritance.

What are the basic concepts of OOP?

The four basic concepts of OOP are:
a.) Abstraction
b.) Polymorphism
c.) Inheritance
d.) Encapsulation

What is dynamic or run-time polymorphism?

– It is also referred to as method overriding. Here, there can be two methods with same name and signature but different implementation.
– The function here is resolved during run time rather than compile time.

What is Inheritance?

– It is the process that allows the objects of one class to acquire the properties of objects of another class.
– The class that inherits is called sub-class while the class from which the object is inherited is called superclass.
– Inheritance helps in re-using the code and polymorphism.

Explain method overriding.

– When a subclass declares a method possessing similar arguments as a method declared by one of its superclass, method overriding takes place.
– Using this technique, the behavior specific to a particular subclass can be defined.
– The methods marked public, final, or static can not be overridden

Can you give some examples of tokens?

Some of the examples of tokens are:
– Keywords,
– Identifiers,
– Constants,
– Operators,
– Brackets,
– Commas.

What is the friend function?

– Friend function is a friend of a class.
– It is allowed to access Public, private or protected data of that class.
– It can be declared anywhere in the class declaration
– It doesn’t have any effect on access control keywords like private, public, or protected.

Define Modularity?

– It is the property of big a system divided into small modules which can be integrated as per the requirement.

Explain a.) Persistence. b.) Collaboration

a.) Persistence.
– It is the property of an object which extends its existence into space and time.

b.) Collaboration
– Process by which several objects cooperate to deliver a higher-level result.

What is a ternary operator?

– It is also called a conditional operator.
– It is an operator that can take three arguments.
– The data types of arguments and results are different.

What are sealed modifiers?

– Access modifiers cannot be inherited by other methods.
– They can be applied to properties, events, and methods but not to static members.

Explain a.) Static binding b.) Dynamic binding

a.) Static binding-
It is a binding in which the name of the class can be associated with it during compilation. Also referred to as early binding.

b.) Dynamic binding –
It is a binding in which the name of the class can be associated with it during execution time. Also referred to as late binding.

What are the different ways for a method to be overloaded?

A method can be overloaded by:
– Varying the numbers of parameters
– Using different data types for the parameters
– Using different sequences of the parameters.

What is composition? Explain the purpose of the composition.

Assembling existing components instead of creating new ones is called composition. In OOP it is called as objects composition. It is the process of placing an object in another object. It is the model of has-a relationship. An employee object can contain an object of type project which is another object.

Purpose of composition:
A model by value aggregation can be derived by using a composition that is semantically equivalent to an attribute.

The lifetime is a coincident part as a whole for both objects

If one part is removed, the whole part also removed without explicit removal of individual parts

The composition can be used to model by-value aggregation which is semantically equivalent to an attribute.

What is an abstraction and why is it important?

Representing essential features by hiding the background process/details. In other words, it is specifying what to do but not how to do.

Abstraction is important at the conceptual level of an application. It helps in understanding clearly, what the process and the flow of an application. The abstraction allows the complete flow and development of an application into a structured action. The conceptual level of project execution is derived from abstraction which the gateway for the entire application development.

How a program can be structured using the concept of Object-oriented programming?

The program can be structured by splitting the one big task into subtasks, creating some function for the tasks that have to be worked upon and then writing a program to instruct the computer to perform the desired calculations on the basis of which the output will be generated. As a large amount of data or tasks will be separated into less complex programs then it will be easier to manage. In an object-oriented program, the program structure is maintained according to the objects made up from the class. Every function is in a particular class that has an object calling certain properties and methods for implementation. It can manage the complexity of the large pieces and will be able to create a modular approach towards the programming methodology.

What are the features that are provided to make a program modular?

Creating a program requires self-sufficient resources, the way to make a piece of code modular so that it can be handled properly. This shows the relationship between different objects or in between the same objects. Different functions have to be used to keep the code different from the data provided. Object-oriented programming allows creating a modular approach to make it more abstract and create the interactions between them.
The features that are being provided in object-oriented programming is:
• Encapsulation: it deals with the grouping of data and functions together at one place or it can be said in an object that defines the interface of their interaction and the relationship between them.

• Inheritance: it deals with the relationship that exists between the parent and child classes. A child can inherit the properties of the parent and it remains helpful in creating a hierarchy in the system to keep things more modular.

• Polymorphism is a feature that deals with different values that can be used by only one function. It doesn’t have to re-create the same function again and again for different values but, it uses the same function to call different data types.

Write a program to show the inheritance used in a class.

Inheritance is a way to define the hierarchy of the related classes. It allows property sharing from one class to another class. It is an easy way to inherit the properties of the parent by the child and use the same properties again and again without redefining the class. The program is as follows it shows a class student that inherits the properties (methods+ data) from the teacher class.

class teacher
{
public:
t(){}
};class student : public teacher
{
public:
s(){}
};void use(teacher const& some)
{
some.t();
}

What is the function of pure virtual functions?

Pure virtual function in object-oriented programming is called a virtual method that acts as a function allowing its behavior to be overridden by the class that is inheriting the pure virtual function with the same signature. This is used in case of polymorphism. It is used when a base class is being driven by the derived class and an object of the derived class referred as base or derived class type. When a derived class overrides the base class method then the output or the behavior will be called as ambiguous. To use the virtual function a virtual keyword is used. This allows the function to be defined in every derived class and use the functionality of it.

What is the syntax of the object-oriented method call?

The object-oriented syntax tells about the object-oriented features and methodologies that are present and shown as:

class teacher
{
// properties of the teacher
String name[];
int numb;// behavior
public void()
// this is the function that is given and it will include all your code
}

int strcmp(const char *, const char *);

int strcasecmp(const char *, const char *);

int (* compare)(const char *, const char *);

if ( **argv == 'i' )

compare = strcasecmp;

else

compare = strcmp;