[Q] mechanism of GlassPane

[Geon Goo]

Hello.
can I ask a question?
my question is about GlassPane.
I know that the glasspane is on top of all components in JFrame.
I tried to setVisible(true) and setOpaque(true) on glasspane.
and in the contentPane, I added a JButton.
in that case, the button I added is invisible(because glasspane covers all). but it works.(why?)
I think when the glasspane gets an AWTEvent, this event is forwarded to contentpane. but I can't find the source code that doing such thing.
would you tell me the principle about that?
thanks