Paint drawing unscrolled graph over scrolled graph! JScrollPane JViewport

Question

I am planning to create a JScrollPane that has a scrollable JPanel. I have created a special paint method for the JPanel.
The JPanel contains a simple graph.
The graph will be scrolled with the JScrollPane.
evreything is good until now.
I want to draw (over the JPanel) another graph which I dont want it to be scrolled by the JScrollPane.
I want: When moving the scrolls, the graph moves but the special graph does not get effected.
I planned to overrirde the paint method of the JViewport object. I can see that the plan is good and the result is 80% pluasable, however, I am experiencing some effects:
1- sometimes the special graph does not get painted!
2- sometimes when moving the scrolls the up and down, the special graph does move, as if the contents are not updated.
I am using Java 5 update 6!
Here is my code, please test it your self:
package test;
import javax.swing.*;
import javax.swing.event.*;
import java.util.*;
import java.awt.*;
import java.awt.event.*;
public class Test{
     public static void main(String[]args){
          JFrame f=new JFrame();
          JPanel p=new JPanel(){
               public void paintComponent(Graphics g){
                    super.paintComponent(g);
                    g.setColor(Color.red);
                    for(int i=0;i<4000;i+=20){
                         g.drawLine(0,i,800,i);
          JViewport port=new JViewport(){
               public void paint(Graphics g){
                    super.paint(g);
                    g.fillRect(0,0,70,70);
          port.setView(p);
          p.setPreferredSize(new Dimension(500,4000));
          JScrollPane pane=new JScrollPane();
          pane.setViewport(port);
          f.add(pane);
          f.pack();
          f.setDefaultCloseOperation(f.EXIT_ON_CLOSE);
          f.setVisible(true);
}

Answer 1

This makes use of the fact that heavyweight/awt components are rendered over lightweight/swing components. Another way to do this is with a glass pane (JRootPane api). The tutorial has an example of glass pane use.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class FloatingControls
    private JPanel getContent()
        JPanel panel = new JPanel();
        OverlayLayout overlay = new OverlayLayout(panel);
        panel.setLayout(overlay);
        panel.add(getControls());
        panel.add(getGraphicComponent());
        return panel;
    private JScrollPane getGraphicComponent()
        JPanel p=new JPanel()
            public void paintComponent(Graphics g)
                super.paintComponent(g);
                g.setColor(Color.red);
                for(int j=0;j<4000;j+=20)
                    g.drawLine(0,j,800,j);
        p.setPreferredSize(new Dimension(500,4000));
        return new JScrollPane(p);
    private JPanel getControls()
        GridBagLayout gridbag = new GridBagLayout();
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.weightx = 1.0;
        Panel awtPanel = new Panel(gridbag)
            public void paint(Graphics g)
                super.paint(g);
                int w = getWidth();
                int h = getHeight();
                g.setColor(Color.blue);
                g.fillRect(0,0,w-1,2);      // top
                g.fillRect(0,2,2,h-5);      // left
                g.fillRect(0,h-3,w-1,2);    // bottom
                g.fillRect(w-3,2,2,h-5);    // right
            public Dimension getPreferredSize()
                // beware of different plaf settings
                return new Dimension(350, 45);
        awtPanel.setBackground(Color.pink);
        for(int j = 0; j < 4; j++)
            awtPanel.add(new JButton("button " + (j+1)), gbc);
        JPanel panel = new JPanel(gridbag);
        panel.setOpaque(false);
        gbc.insets = new Insets(0,5,0,20);
        // an option, works with insets
        //gbc.fill = GridBagConstraints.HORIZONTAL;
        panel.add(awtPanel, gbc);
        return panel;
    public static void main(String[] args)
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setContentPane(new FloatingControls().getContent());
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
}