This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
It's defined in the look and feel. If I set Windows L&F and show a JDialog I get a dialog with only a close button. If I set Metal L&F I get a dialog with no buttons at all. If I set Motif L&F... I get a Windows dialog with motif widgets inside of it. (Even if I call JDialog.setDefaultLookAndFeelDecorated( true )) Unfortunately my Linix box is at home, so I can't test it out for sure, but I assume I would get the same results as you.
Write once, run anywhere, because there's nowhere to hide! - /. A.C.