How is the 'code fold' functionality implemented?

Question

Hi all,
I'm thinking that I'd like to have a form, which is broken into several categories, that has 'code fold' functionality ala NetBeans. I'm thinking the way to do this would be to simply place all of these JPanels in the form in the nodes of a tree, when collapsed, just the title is displayed, when they expand, the JPanel appears. I admit I've not yet tried this approach yet , I first wanted to find out if anyone has done something like this and what approach they might use. Any feedback is appreciated.
Thanks
Mike

Answer 1

I read this and thought it would be great to have in my own app.
So, after getting some code from these forums I have cobbled together the following classes.
This one creates a collapsible panel:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.LayoutManager;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.border.LineBorder;
* CollapsiblePanel.java Created on 22-Apr-2005
public class CollapsiblePanel extends JPanel
    private class TitlePanel extends JPanel
        private Color fadeto = new Color(200, 212, 247);
        public TitlePanel(LayoutManager layout)
            super(layout);
        protected void paintComponent(Graphics g)
            GradientPaint gradient = new GradientPaint(0, 0, Color.white,
                    getSize().width - 10, getSize().height, fadeto, true);
            Graphics2D g2d = (Graphics2D) g;
            g2d.setPaint(gradient);
            g2d.fill(new Rectangle(getSize().width, getSize().height));
    private JPanel mPanel = new JPanel(new GridLayout(0, 1, 2, 2));
    private JLabel mTitle;
    private JLabel mButton;
    public CollapsiblePanel(String title)
        setLayout(new BorderLayout());
        final Color active = new Color(66, 142, 255);
        final Color inactive = new Color(33, 93, 198);
        final ImageIcon up = new ImageIcon("Up.gif");
        final ImageIcon down = new ImageIcon("Down.gif");
        mTitle = new JLabel(title);
        mTitle.setForeground(inactive);
        mButton = new JLabel(up);
        TitlePanel panel = new TitlePanel(new BorderLayout());
        panel.setBorder(new LineBorder(Color.BLACK));//EmptyBorder(2, 2, 2, 2));
        panel.add(mTitle, BorderLayout.CENTER);
        panel.add(mButton, BorderLayout.EAST);
        panel.addMouseListener(new MouseAdapter()
            public void mouseClicked(MouseEvent e)
                mPanel.setVisible(!mPanel.isVisible());
                mButton.setIcon(mPanel.isVisible() ? up : down);
            public void mouseEntered(MouseEvent e)
                mTitle.setForeground(active);
            public void mouseExited(MouseEvent e)
                mTitle.setForeground(inactive);
        panel.setBackground(Color.WHITE);
        mPanel.setBorder(new EmptyBorder(2, 2, 2, 2));
        //mPanel.setBackground(new Color(214, 223, 247));
        add(panel, BorderLayout.NORTH);
        add(mPanel, BorderLayout.CENTER);
    public Component add(Component comp)
        return mPanel.add(comp);
}This one creates a panel to hold many collapsible panels.
NOTE: This uses the TableLayout manager which can be found on the web. I am sure that all of you here could change it to use GridbagLayout.
import javax.swing.JPanel;
import info.clearthought.layout.TableLayout;
* Panel to hold many CollapsiblePanels
* @author Garry Lovesey
* @version 1.0 22-Apr-2005
public class CollapsiblePanelBar2 extends JPanel
    public static double PREFERRED = TableLayout.PREFERRED;
    public static double FILL = TableLayout.FILL;
    private TableLayout layout;
    public CollapsiblePanelBar2(CollapsiblePanel panel, double layoutPreference)
        super();
         // create the GUI
          // b - border
          // f - FILL
          // p - PREFERRED
          // vs - vertical space between labels and text fields
          // vg - vertical gap between form elements
          // hg - horizontal gap between form elements
          double b= 10;
          double f= TableLayout.FILL;
          double p= TableLayout.PREFERRED;
          double vs= 5;
          double vg= 10;
          double hg= 10;
          double size[][]= { { f }, { // our column sizes
               layoutPreference }}; // our row sizes
          layout= new TableLayout(size);
          setLayout(layout);
          // now we add in our starter panel
          add(panel, "0,0");
    public void add(CollapsiblePanel panel, double layoutPreference)
          // we need to add our panel into our layout
        int rowToAdd = layout.getNumRow();
        layout.insertRow(rowToAdd, layoutPreference);
        add(panel, "0," + rowToAdd);
}