Actually, because of the nature of how the tab key works, you have to disable the default event for tab before you can trap the tab event with a FocusListener. So
you should use this method:
combo.setFocusTraversalKeysEnabled(false);
Just remember that in your FocusEvent method where you do your work, if you want it to then tab to the next component, you have to code that manually by requesting focus on the next component (since you disabled the tab ability).
The other option is what was already suggestion, I will just elaborage a bit. If you want to use the ENTER key instead of tab, you would want to use an ActionListener with an ActionEvent and pressing ENTER will trigger this action. Again, if you want focus to change to the next component after ENTER is pressed, you will need to code that move manually, or you will have to hit enter and then hit tab to move.
Hope that helps.