How to create expandable panels using swing?

I would like to create a list of expandand/collapse panels, like on this image:

I haven't found any swing component for this, so I began to create something like this. I tried to put buttons one under the other, which fill the available width, but doesn't really works. I can only see the last added one.

    JPanel panel = new JPanel();
    panel.setLayout(new BorderLayout());

    panel.add(new JButton("Delphi Projects"), BorderLayout.NORTH);
    panel.add(new JPanel(), BorderLayout.NORTH); // hidden panel
    panel.add(new JButton("Delphi Projects | Delphi Files"), BorderLayout.NORTH);
    panel.add(new JPanel(), BorderLayout.NORTH); // hidden panel
    panel.add(new JButton("Other Files"), BorderLayout.NORTH);
    panel.add(new JPanel(), BorderLayout.NORTH); // hidden panel
    panel.add(new JButton("C++ Builder Projects | C++ Builder Files"), BorderLayout.NORTH);
    panel.add(new JPanel(), BorderLayout.NORTH); // hidden panel

    JScrollPane scroll = new JScrollPane(panel);

You can take a look to JXTaskPaneContainer and JXTaskPane from SwingX project which have these advantages:

• They are components just like a JPanel is so no extra effort is required to work with them.
• Unlike accordions you can have more than one panel expanded at any time.
• They have a cool and smooth effect on collapsing/expanding events.
• Unlike trees/tree tables you don't have to mess with either TreeModel nor TreeTableModel at all. Also trees and tree tables are components intended to show data in a hierarhical form, not to add components into it.

If you don't like task panes and want to implement something on your own then you have JXCollapsiblePane (also available in SwingX API).

Check SwingLabs Demos for a complete set of SwingX components demo.

Screenshot