Menu Mnenomics are not working when menu added directly to JFrame.

Steps to reproduce:
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1)Make a Frame and add a menu with Mnemonic on it(Suppose 'f').
2) You will see 'F' with an underscore. Now press alt + f.
3) Nothing happens.
This behavior is wrong. Either the Menu should show the drop down or there should be no Mnemonic shown.

Also the JDk Docs,
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"In essence, a menu is a button with an associated JPopupMenu. When the "button" is pressed, the JPopupMenu appears. If the
"button" is on the JMenuBar, the menu is a top-level window. If the "button" is another menu item, then the JPopupMenu is
"pull-right" menu. "
===============================================================================,
does not tell what will be the bahavior of the JMenu if it is not added on JMenuBar.