What is the difference between base reference type vs derived reference type

Question

class Dog
{
}
class BullDog : Dog
{
}
class Program
{
    static void Main()
    {
        Dog dog2 = new BullDog();
        BullDog dog3 = new BullDog();
    }
}
         


        

Answer 1

lets define an other class :

class OtherDog : Dog 
{

}

now you can define a list like this :

C# :

List Dogs = new List();
Dogs.Add(new BullDog());
Dogs.Add(new OtherDog());

you have a list with Dog type , but can add to it BullDog and OtherDog type to it

this is one of the OOP subjects name "Polymorphism"

ex2 :

lets think you want to develop a paint :

class Shape ()
{

    virtual public void Draw()
    {
    }

}

class Rectangle : Shape ()
{

    override public void Draw()
    {
    }

}

class Circle : Shape ()
{

    override public void Draw()
    {
    }

}


void main ()
{

    List Shapes = new List();
    Shapes.Add(new Rectangle());
    Shapes.Add(new Circle());

    Shape[1].Draw(); //Draw a rectangle
    Shape[2].Draw(); // Draw a circle

}

if you need more details comment me to edit my reply for more details

thansk , Ali