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);

