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Top 10 OOPs concepts Interview Questions in C# with code

Top 10 OOPs concepts Interview Questions in C# with code

C# is a powerful, object-oriented programming language that is widely used for developing desktop, web, and mobile applications.

Mastering Object-Oriented Programming (OOP) concepts in C# is crucial for any developer aiming to excel in this field.

In this blog, we'll explore some of the most commonly asked OOP-related questions in C# interviews, providing insights and answers that can help you prepare effectively.

Page Contents

1. What is Object-Oriented Programming (OOP)?

2. Can you explain the concept of a class and an object in C#?

3. What is encapsulation in C# and how is it implemented?

4. What is inheritance and how does it work in C#?

5. What is polymorphism in C# and how is it achieved?

6. What is abstraction and how is it implemented in C#?

7. What are constructors and destructors in C#?

8. What is the difference between abstract class and interface in C#?

9. What is the purpose of the this keyword in C#?

10. How is exception handling implemented in C#?

1. What is Object-Oriented Programming (OOP)?

Object-Oriented Programming (OOP) is a programming paradigm that uses objects and classes to design and develop applications. The key principles of OOP are:

  • Encapsulation: Bundling the data (attributes) and methods (functions) that operate on the data into a single unit or class, and restricting access to some of the object's components.
  • Inheritance: A mechanism where a new class (derived class) inherits properties and behavior (methods) from an existing class (base class).
  • Polymorphism: The ability of different classes to be treated as instances of the same class through a common interface, typically achieved through method overriding and overloading.
  • Abstraction: Hiding the complex implementation details and showing only the necessary features of an object.

2. Can you explain the concept of a class and an object in C#?

Class: A class is a blueprint or template that defines the properties and behaviors (methods) that the objects created from the class can have. For example:

public class Car
{
    public string Make { get; set; }
    public string Model { get; set; }

    public void Drive()
    {
        Console.WriteLine("Driving the car");
    }

}

Object: An object is an instance of a class. It is created from a class and can access the properties and methods defined in the class. For example:

Car myCar = new Car();

myCar.Make = "Toyota";

myCar.Model = "Corolla";

myCar.Drive();

3. What is encapsulation in C# and how is it implemented?

Encapsulation is the process of bundling the data (fields) and methods that operate on the data into a single unit, typically a class, and restricting access to the inner workings of that class. It is implemented using access modifiers such as private, protected, internal, and public. For example:

public class Account
{
    private decimal balance;

    public void Deposit(decimal amount)
    {
        if (amount > 0)
        {
            balance += amount;
        }
    }

    public decimal GetBalance()
    {
        return balance;
    }

}

In this example, the balance field is private and can only be accessed through the Deposit and GetBalance methods.

4. What is inheritance and how does it work in C#?

Inheritance is a feature of OOP that allows a class to inherit properties and methods from another class. The class that inherits is called the derived class or child class, and the class being inherited from is called the base class or parent class. This promotes code reuse and establishes a hierarchical relationship between classes. For example:

public class Animal
{
    public void Eat()
    {
        Console.WriteLine("Eating");
    }
}

public class Dog : Animal
{
    public void Bark()
    {
        Console.WriteLine("Barking");
    }
}

In this example, Dog inherits the Eat method from Animal and adds its own method Bark.

5. What is polymorphism in C# and how is it achieved?

Polymorphism is the ability of different objects to be treated as instances of the same class through a common interface. It is achieved through method overriding and method overloading.

  • Method Overriding: Allows a derived class to provide a specific implementation of a method that is already defined in its base class using the override keyword. For example:
public class Animal
{
    public virtual void Speak()
    {
        Console.WriteLine("Animal sound");
    }
}

public class Dog : Animal
{
   public override void Speak()
    {
        Console.WriteLine("Bark");
    }
}
  • Method Overloading: Allows a class to have multiple methods with the same name but different parameters. For example:
public class MathOperations
{

    public int Add(int a, int b)
    {
        return a + b;
    }

    public int Add(int a, int b, int c)
    {
        return a + b + c;
    }

}

6. What is abstraction and how is it implemented in C#?

Abstraction is the concept of hiding the complex implementation details and showing only the necessary features of an object. In C#, abstraction is implemented using abstract classes and interfaces.

  • Abstract Class: A class that cannot be instantiated and can contain abstract methods, which are methods without implementation. Derived classes must implement the abstract methods. For example:
public abstract class Shape
{
    public abstract double GetArea();
}

public class Circle : Shape
{

    public double Radius { get; set; }

    public override double GetArea()
    {
        return Math.PI \*Radius \*Radius;
    }

}
  • Interface: A contract that defines a set of methods and properties that the implementing class must provide. For example:
public interface IShape
{
    double GetArea();
}

public class Square : IShape
{
    public double Side { get; set; }

    public double GetArea()
    {
        return Side \*Side;
    }
}

7. What are constructors and destructors in C#?

  • Constructors: Special methods that are called when an object is instantiated. They are used to initialize the object. Constructors have the same name as the class and do not have a return type. For example:
public class Person
{
    public string Name { get; set; }

    public Person(string name)
    {
        Name = name;
    }
}
  • Destructors: Special methods that are called when an object is destroyed. They are used to release resources. Destructors have the same name as the class but are preceded by a tilde (~). For example:
public class Person
{
    ~Person()
    {
        // Cleanup code here
    }
}

8. What is the difference between abstract class and interface in C#?

  • Abstract Class: Can have implementations for some of its members (methods, properties). It can also have fields, constructors, and destructors. A class can inherit from only one abstract class.
public abstract class Vehicle
{
    public abstract void Drive();

    public void FillTank()
    {
        // Code to fill tank
    }
}
  • Interface: Cannot have any implementations for its members. It can only have method signatures and properties without implementation. A class can implement multiple interfaces.
public interface IVehicle
{
    void Drive();
}

public interface IFuelable
{
    void FillTank();
}

public class Car : IVehicle, IFuelable
{
    public void Drive()
    {
        // Code to drive
    }

    public void FillTank()
    {
        // Code to fill tank
    }
}

9. What is the purpose of the this keyword in C#?

The this keyword refers to the current instance of the class. It is used to access members of the current class and to distinguish between class members and parameters with the same name. For example:

public class Employee
{
    private string name;

    public Employee(string name)
    {
        this.name = name; // Refers to the class member 'name'
    }
}

10. How is exception handling implemented in C#?

Exception handling in C# is implemented using try, catch, finally, and throw blocks. The try block contains the code that may cause an exception. The catch block handles the exception. The finally block contains code that is executed regardless of whether an exception is thrown or not. The throw keyword is used to throw an exception. For example:

public class ExceptionHandling
{
    public void Divide(int a, int b)
    {
        try
        {
            int result = a / b;
        }
        catch (DivideByZeroException ex)
        {
            Console.WriteLine("Cannot divide by zero.");
        }
        finally
        {
            Console.WriteLine("Division operation completed.");
        }
    }
}

Conclusion

Understanding and mastering OOP concepts in C# is crucial for any developer.

These commonly asked OOPs interview questions cover the fundamental principles and practical implementations of OOP in C#.

By familiarizing yourself with these questions and their answers, you'll be well-prepared to tackle OOP-related questions in your next C# interview. Good luck!

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