Linking a Java JScrollBar to a JTextArea/Custom positioning a JScrollBar (track and thumb)

Question

I have created a JScrollbar (with a custom UI) and a JTextArea in a JScrollPane in a JPanel. I don't want to add the scrollbar as the scrollpane's horizontal scrollbar, because I want to be able to position it.

I tried setting the model on the scrollbar and adding it to the panel (see code), but this didn't work -- the thumb didn't size correctly (it always spanned the entire track) and wasn't positioned correctly.

JPanel panel = new JPanel();
JTextArea textArea = new JTextArea(col, rows);
JScrollPane scrollPane = new JScrollPane(textArea);
JScrollBar scrollBar = new JScrollBar();    
scrollBar.setModel(scrollPane.getHorizontalScrollBar().getModel());
panel.add(textArea);
panel.add(scrollPane);
panel.add(scrollBar)

How can I link a scrollbar to my text area so the thumb sizes and behaves correctly and still be able to set the position and dimensions of my scrollbar?

Thanks!

Answer 1

If you want the default behaviour - you did it already. You need to add some components to your JScrollPane to actually see it.

Below is an example:

public final class Test {
    public static void main(String[] a) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

                Container pane = frame.getContentPane();
                JPanel panel = new JPanel();
                JTextArea textArea = new JTextArea(2, 10);
                JScrollPane scrollPane = new JScrollPane(textArea);
                JScrollBar scrollBar = new JScrollBar();//new JScrollBar(SwingConstants.HORIZONTAL);
                scrollBar.setModel(scrollPane.getHorizontalScrollBar().getModel());
                panel.add(textArea);
                panel.add(scrollPane);

                JPanel internal = new JPanel();
                for(int i = 0; i < 20; ++i) {
                    internal.add(new JLabel("TEXT"));
                }
                scrollPane.setViewportView(internal);
                scrollPane.setPreferredSize(new Dimension(100, 100));
                panel.add(scrollBar);
                pane.add(panel);
                frame.pack();
                frame.setLocationRelativeTo(null);

                frame.setVisible(true);
            }
        });
    }
}