Try:
myJButton.setMnemonic('b');

This is assuming you are in swing and using JButtons of course. Probably will
work with AWT heavyweight buttons. This setMnemonic method will allow you to
hit "ALT + B" and the button  will think it got clicked.

And do you have any idea how to add  underline to one of the letters of
JButton text ? This is applicable to inform the user that he could use
Alt + underlined_letter instead of clicking the button.

And do you have any idea how to add  underline to one of the letters of
JButton text ? This is applicable to inform the user that he could use
Alt + underlined_letter instead of clicking the button.

When you use the underlined letter to show that you can use alt-key as a
shortcut, the menu item has to be visible for the user to do so. It is better
to have ctrl-key shortcuts to the side of the menu item. Often, by the time
someone finds what they are looking for, they might as well move the mouse to it
as to find it then hit the alt-key combination.

Sorry, yes it works. I failed to notice that before.
Thank's for your help.