Swing programmers use custom RepaintManagers to implement various visual effects
that are not directly supported in Swing.

The famous example is given in the chapter #11 of the "Filthy Rich Clients" book
where this trick is used to implement a reflection of the Swing panel content

Changing a RepaintManger leads to some unwanted effects like disabling the
"gray rect fix" and generally is not recommended by the Swing team.

http://weblogs.java.net/blog/2008/04/13/repaintmanagers-side-effect

We should provide a more simple and natural way to implement for this kind of effects,
JPanel should be able to catch the repaintings of its children.