Derived Classes

When we say a class is derived from another class, it means that it has all the fields and methods of the parent class and in addition to it, the derived class can contain additional fields and methods as well.

The syntax for making an inherited class is the following:

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// Base class (parent class)
public class BaseClass
{
    // Fields and methods of the base class
}

// Derived class (child class)
public class DerivedClass : BaseClass
{
    // Additional fields and methods specific to the derived class
}

Here's an example with some concrete code:

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using System;

// Base class (parent class)
public class Animal
{
    public string Name;

    public void Eat()
    {
        Console.WriteLine($"{Name} is eating.");
    }
}

// Derived class (child class)
public class Dog : Animal
{
    public void Bark()
    {
        Console.WriteLine($"{Name} is barking.");
    }
}

class ConsoleApp
{
    static void Main()
    {
        // Creating an instance of the derived class
        Dog myDog = new Dog();
        myDog.Name = "Buddy";

        // Using inherited method from the base class
        myDog.Eat();

        // Using method specific to the derived class
        myDog.Bark();
    }
}

In this example, Dog is the derived class, inheriting from the Animal base class. The Dog class has access to the Name property and the Eat method from the Animal class. Additionally, it introduces a new method, Bark, which is specific to the Dog class.

As illustrated in the diagram, there can be cases where a class inherits from a class which is already a class from some other:

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using System;

// Base class
public class Animal
{
    public void Eat()
    {
        Console.WriteLine("Animal is eating.");
    }
}

// Intermediate class inheriting from Animal
public class Mammal : Animal
{
    public void GiveBirth()
    {
        Console.WriteLine("Mammal is giving birth.");
    }
}

// Derived class inheriting from Mammal
public class Dog : Mammal
{
    public void Bark()
    {
        Console.WriteLine("Dog is barking.");
    }
}

class Program
{
    static void Main()
    {
        Dog myDog = new Dog();
        
        // Methods from the base class
        myDog.Eat();

        // Methods from the intermediate class
        myDog.GiveBirth();

        // Methods from the derived class
        myDog.Bark();
    }
}

In such a case, the class at the top-most level is called the Super Class. In this case Animal is the super class. Such a case where where there are multiple levels of inheritence is called Multi-Level Inheritence.

1. In C#, which keyword or symbol is used to declare a derived class?

2. In Multi-Level inheritance, what is the class at the top called?

3. Is Multilevel inheritance possible in C#?

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