An object of type DrawableIterator can be obtained by invoking the
getDrawableIterator method of a DrawaingCanvas and then used to write
loops that sequentially process all the Drawable objects displayed
on the associated canvas.
This predefined method is invoked by the appletviewer or web browser running
a program that extends AWTController when the program's execution is complete.
This predefined method is invoked by the appletviewer or web browser running
a program that extends Controller when the program's execution is complete.