title: alternatives/improvements to JSplitPane
body: <p>I had a fairly simple dialog with a pair of JPanels of roughly equal size, contained in a JSplitPane. Now I'm looking at adding a 3rd JPanel and I'm not so sure there is an obvious solution. Is there a good window-docking framework out there? or is that a horribly complex thing to get into? If I do just stick with the 3-panel split, do I have to use a pair of nested JSplitPanes or is there an alternative that allows a 3-way split?</p>