🚀 go-pugleaf

Hi All,
  I'm starting to learn JBuilder and ran across a demo that uses the Image
abstract class,
  using createImage it. What I fail to understand is how can I later use
it's methods
  when this class is declared as abstract ? Also if there is an underlying
class that
  I've failed to notice, which one is it ?
  Following is the code :

   Image im = createImage ( getSize().width, getSize().height );
   Graphics buf = im.getGraphics();

TIA,
  Eyal.