Downcasting

Now, we will talk about downcasting, which means going from, for example, a parent type to a child type. Enter the following between a set of curly braces below this line:

sampLabel.Text += ((Square)lst[0]).Perimeter();

Now, beneath the closed curly brace after the preceding line, enter the following:

else if(lst[0] is Rectangle)

Then, you can call the following code; so, copy the sampLabel.Text... line and paste it between a set of curly braces:

sampLabel.Text += ((Rectangle)lst[0]).Perimeter();

Be sure to change Square to Rectangle, so that it gets cast down to a rectangle, and then the Perimeter function on the rectangle will be called. When you hover your mouse over Perimeter in the preceding two lines, the popups show string Square.Perimeter() and string Square.Perimeter(), respectively. If you removed (Rectangle) from the preceding line and hovered your mouse over Perimeter, the popup will show string Quad.Perimeter(). Do you understand? This is why I have the cast: because it changes the way the functions are recognized.

This is downcasting from a parent to a child class. So, when we talk about bulk actions, you cannot cast to a parent class, perform a bulk action like a sort, or if you want to add refinements called child classes and child class objects, then you can downcast.