Top 14 OOPs Interview Questions and Answers

Question

1. What is the concept of OOPs?

Answer 1

OOPs or Object Oriented Programming systems have a certain set of principles or concepts to write good programming logic. Basic OOPs concepts include:

Answer 2

Object Oriented programming systems organize or manage the code by creating types in the form of classes. A Class contains the code that represents a specific entity and defines what an entity can do. For example, A BankAccount entity can be organized by a class 'BankAccount'.
An entity has certain behavior, The code implements this behavior in the form of operations or functions using Methods and Properties.
An Object is a block of memory that has been configured and allocated according to the entity - which exists in the form of class.

Answer 3

When you see the word 'object-oriented', there are other terms such as object-oriented programming, object-oriented design and object-oriented analysis. All these three terms are inter-related as to understand the problem, design the solution and build it or in simple terms analysis, design and programming.

Answer 4

Imagine you have a car, and you want to use it to travel from one place to another. When you interact with the car, you don't need to know the intricate details of how the engine works, how the transmission system functions, or how the electrical components are wired. All you need to know is how to use the steering wheel, accelerator, and brake pedals. This is an example of abstraction.
Abstraction is the process of hiding complex implementation details and exposing only the essential features and behaviors that are relevant to the user or client. In OOP, you can achieve it through interfaces and abstract classes. They define a contract or a blueprint of what operations a class should provide, without specifying the implementation details.
For example, consider an abstract class called Shape that defines methods like CalculateArea(), CalculatePerimeter(). Any class that implements this abstract class must provide implementations for these methods. However, the implementation details can vary based on the type of shape (circle, rectange).


    // Abstract class
public abstract class Shape
{
    public abstract double CalculateArea();
    public abstract double CalculatePerimeter();
}
// Concrete class
public class Circle : Shape
{
    private double radius;
    public Circle(double radius)
    {
        this.radius = radius;
    }
    public override double CalculateArea()
    {
        return Math.PI * radius * radius;
    }
    public override double CalculatePerimeter()
    {
        return 2 * Math.PI * radius;
    }
}
// Usage
Circle circle = new Circle(5);
double area = circle.CalculateArea(); // Output: 78.53981633974483
double perimeter = circle.CalculatePerimeter(); // Output: 31.41592653589793

In this example, the Shape abstract class defines the contract (method signatures) for calculating the area and perimeter of a shape. The Circle class implements this contract by providing the specific implementation for a circle. The user of the Circle class does not need to know the details of how the area and perimeter are calculated; they only need to know the methods they can call.

Answer 5

Encapsulation allows to hide internal state and functionality of objects. It allows access through a public set of properties or functions. Encapsulation provides the ability for a class to specify how accessible each of its members to the code outside of this class. Members of the class which are not intended to be used outside of this class can be hidden to limit potential for coding errors. For example, Let's consider a scenario where you have a BankAccount class that needs to manage the account balance and allow depositing and withdrawing funds.

public class BankAccount
{
    private double _balance;

    public double Balance
    {
        get { return _balance; }
    }

    public void Deposit(double amount)
    {
        _balance += amount;
    }

    public void Withdraw(double amount)
    {
        if (amount <= _balance)
        {
            _balance -= amount;
        }
        else
        {
            Console.WriteLine("Insufficient funds.");
        }
    }
}

By encapsulating the _balance field and providing methods to interact with it, you enforce data integrity and prevent the balance from being set to an invalid value. Additionally, the Withdraw method includes a check to ensure that the withdrawal amount doesn't exceed the available balance, maintaining the account's integrity.

This encapsulation approach promotes code organization, maintainability, and data protection, as the internal implementation details of the BankAccount class are hidden from the outside world, and the class provides a well-defined interface for interacting with its functionality.

Answer 6

Inheritance is a key concept in Object-Oriented Programming (OOP) that allows a new class (derived class or child class) to inherit properties and methods from an existing class (base class or parent class). It enables code reuse by letting derived classes acquire the characteristics of the base class, while also allowing them to add their own unique features or override inherited behavior.

Inheritance establishes an "is-a" relationship between classes, where the derived class is considered a specialized version of the base class. For example, a "Car" class can inherit from a "Vehicle" base class, inheriting properties like "make" and "model," and methods like "start" and "stop."

Through inheritance, common functionality is defined in the base class and automatically shared among all derived classes, promoting code organization and reducing duplication. If changes are made to the base class, all derived classes inherit those changes, ensuring consistency and maintainability.

Example:


// Base class
public class Vehicle
{
    public string Make { get; set; }
    public string ModelName { get; set; }

    public void StartEngine()
    {
        Console.WriteLine("Engine started.");
    }
}

// Derived class
public class Car : Vehicle
{
    public int NumberOfDoors { get; set; }

    public void OpenTrunk()
    {
        Console.WriteLine("Trunk opened.");
    }
}

// Usage
Car myCar = new Car
{
    Make = "Toyota",
    ModelName = "Camry",
    NumberOfDoors = 4
};

myCar.StartEngine(); // Output: Engine started. (Inherited method)
myCar.OpenTrunk(); // Output: Trunk opened. (Derived class method)

When we create an instance of Car, we can call both the inherited method StartEngine from the base class Vehicle, as well as the OpenTrunk method defined in the derived class Car.
This example demonstrates how inheritance allows code reuse by inheriting common properties and methods from a base class, while also providing the ability to add specialized behavior in derived classes.

Answer 7

Polymorphism is the ability of an object to take on many forms or behaviors. It allows objects of different classes to be treated as objects of a common base class, while still executing the correct implementation based on the actual object type.
For example,


// Base class
public class Vehicle
{
    public virtual void StartEngine()
    {
        Console.WriteLine("The vehicle's engine has started.");
    }
}

// Derived class
public class Car : Vehicle
{
    public override void StartEngine()
    {
        Console.WriteLine("The car's engine is starting.");
    }
}

// Derived class
public class Motorcycle : Vehicle
{
    public override void StartEngine()
    {
        Console.WriteLine("The motorcycle's engine is starting.");
    }
}

// Usage
Vehicle myVehicle1 = new Car();
Vehicle myVehicle2 = new Motorcycle();

myVehicle1.StartEngine(); // Output: The car's engine has started with a smooth purr.
myVehicle2.StartEngine(); // Output: The motorcycle's engine has started with a loud roar.

In this example, the base class Vehicle has a virtual method StartEngine(). The derived classes Car and Motorcycle override this method with their own implementations.
When instances of Car and Motorcycle are assigned to variables of the base class type Vehicle, and the StartEngine() method is called on these variables, the appropriate overridden implementation from the derived class is executed.
This demonstrates method overriding, which is a form of polymorphism. It allows objects of different classes to be treated as objects of a common superclass, while still executing the correct implementation based on the actual object type.
It is achieved through mechanisms like method overriding (as demonstrated in the example) and method overloading, and it promotes code modularity, maintainability, and extensibility.

Answer 8

The concept of Aggregation is a type of another relationship in which one object is composed of other objects but the lifetimes of objects not tied to each other. So Aggregation is referred to as a 'has a relationship' between objects but it does not imply ownership. For example, A Department has many employees so we can say Department Object has collection of employee objects and lifetime of employees not tied to each other or the existence of department. If we remove employee, the department can continue to exist and If we end the department the individual employee can continue to exist and do their own thing.

Answer 9

Composition is a more specific form of Aggregation. It is based on a 'has a relationship' between objects but it implies ownership. For example, A car has an engine or it owns an engine. Composition implies ownership so an engine has no purpose without a car. In composition, if the owning object is destroyed the contained objects are destroyed too. So in Programming if you are defining a owning class, you may need to write constructor and destructor methods to take care of creating and deleting internal objects.

Answer 10

Association is referred to as a structural relationship between the classes of objects where one object instance causes another to perform some operation on its behalf. Association does not represent the behavior rather than It allows to associate one type of objects with another type of objects. Association relationships can be one-to-one, one-to-many, many-to-one and many-to-many. For example, A Role can belong to one or many users and One User may have one or more than one role.

Answer 11

Delegation allows the objects to perform some operations or actions beyond the scope of the object. For example, Some Parents are working professionals, so they hire a baby caretaker. But what will happen if the baby gets sick? There is a note on the table "In case of emergency, please call XYZ on 999-999-999". So XYZ is the delegate here.

    
            //parent class
            babyCareTaker.delegate = XYZ
            [babyCareTaker lookAfter:baby]

            //babyCareTaker class
            if (baby.isSick)
            {
            [delegate callAbout:baby]
            }

Every object-oriented programming supports the concept delegates. For more visit Delegation.

Answer 12

Cohesion is the degree of measure that tells how well-focused a class is designed. A class designed with a single business responsibility ensures high cohesion and It should implement the methods which are intended for a well focused purpose. A benefit of high cohesion is that classes are easier to maintain and provide better readability and reusability.

Answer 13

Coupling is a degree of measure that indicates how closely connected two classes are. If the coupling is high then changes in one class affects the code in other classes and makes code difficult to maintain and change. Applications with low coupling ensure better code maintainability and any code changes can be easily implemented without affecting other classes or systems. A good application design must have High Cohesion and Low Coupling.

Answer 14

Use Case Diagram defines the possible interactions of a user with the system. It encapsulates the system behavior, use cases and different actors of the system. Use-case diagrams are useful during the analysis and design phase to identify the required classes and tests for the system. Use-case diagram shows how the actors use the system rather than how the system works internally. For more visit Use-case diagrams.

Answer 15

When you attend an interview, Interviewer may ask you to rate yourself in a specific Technology like OOPs, So It's depend on your knowledge and work experience in OOPs. The interviewer expects a realistic self-evaluation aligned with your qualifications.

Answer 16

The challenges faced while working on OOPs projects are highly dependent on one's specific work experience and the technology involved. You should explain any relevant challenges you encountered related to OOPs during your previous projects.

Answer 17

This question is commonly asked in interviews to understand your specific responsibilities and the functionalities you implemented using OOPs in your previous projects. Your answer should highlight your role, the tasks you were assigned, and the OOPs features or techniques you utilized to accomplish those tasks.

Answer 18

Here you can tell about your overall work experience on OOPs.

Answer 19

Whether a candidate has completed any OOPs certification or training is optional. While certifications and training are not essential requirements, they can be advantageous to have.

Answer 20

We have covered some frequently asked OOPs Interview Questions and Answers to help you for your Interview. All these Essential OOPs Interview Questions are targeted for mid level of experienced Professionals and freshers.
While attending any OOPs Interview if you face any difficulty to answer any question please write to us at info@qfles.com. Our IT Expert team will find the best answer and will update on the portal. In case we find any new OOPs questions, we will update the same here.

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Top 14 OOPs Interview Questions and Answers

OOPs Interview Questions and Answers

Some General Interview Questions for OOPs

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