I believe that you have to use some root container but that it doesn't have to be a JFrame. You could use a JDialog, a JOptionPane, or a JWindow. You could set your app to have no "decorations", no titlebar, or resize/exit buttons if desired. I suggest that you study the Sun Swing tutorials for more detail. Good luck.
Pete Stein is correct, but the actual list of top-level containers is (I think) Window Frame Applet and Dialog. Frame includes JFrame (as a subclass) (etc), and what you get from JOptionPane is actually a Dialog.
No, they are still in a Frame. I've retrieved it for showing modal dialogs.
Of course you should treat Applets as top-level as far as creating components goes (i.e. you don't add it to anything yourself), but it certainly is not a top-level component in the same way as Frame or Dialog are. [ October 23, 2008: Message edited by: Rob Prime ]