The Macintosh merges the selected windows menubar with the system
menubar that's always visible at the top of the screen. The Swing
JRootPane container, which is the default (only) child of JFrame,
JDialog, and JWindow, always locates the menubar in a horizontal band
above its contentPane child. This matches the layout of menubars for
most look and feels, but not the Macintosh. We propose to modify
Swing so that the MacLookAndFeel from Apple can merge Swing menubars
with the Apple desktop menubar.