Image class and constructor of Bitmap type?

Well I do not understand how it comes that Image class has a constructor of Bitmap type? 开发者_运维问答I mean, I can do:

Image sprite=new Bitmap(...)

Why? Its because Bitmap is derived from Image?

Yes, because Image is abstract, but Bitmap, which extends Image is not. You could just as easily have your code do this instead:

Bitmap sprite = new Bitmap();

The reason why Image is abstract is because it can also represent non-pixel-based images.

Why? Its because Bitmap is derived from Image?

Well, yeah, that's what MSDN says (assuming System.Drawing namespace):

[SerializableAttribute]
[ComVisibleAttribute(true)]
public sealed class Bitmap : Image

But it's not the Image class that has a Bitmap() constructor. Since Bitmap inherits from Image, all instances of Bitmap are also instances of Image.