I am working my way through an online book--Intro to Java Programming by David Eck--and in it he says that it is generally considered bad style to use the getGraphics() method to draw outside of a component's paintComponent method. Does anyone know why this is?
Since nobody more knowlegable has answered, here's my attempt.
Swing thinks that it is in charge of what gets painted when because it is responsible for calling the various paint methods. If you go ahead and do painting activities that Swing doesn't know are happenuing then either they won't make it all the way to the screen or they will get over-painted at random by Swing.