How to place a JSlider in the middle of an image?

Question

Hi,
Here is the deal. I have an image inside a JLabel. That JLabel is inside a JPanel, which in turn is encompassed by a JScrollPane. This image represents some curve or a frequency function, lets say for instance a sine curve. What I need to do is have a slider, positioned (just to keep things simple for now) in the middle of that image, not above or below or to the side of an image, but rather directly over it. Thus, blocking a small section of the image from view. So that the user can drag the mouse cursor along the (horizontal) slider and see the different values on that curve. I dont know of any LayoutManager that would allow me to place a JSlider at an arbitrary position on top of a JLabel, besides just using a Null Layout. However, when I use a Null Layout my scroll bars disappear and the JSlider itself just sits there doing nothing, without reacting to any mouse movements, and mroe importantly as soon as the application is resized, the JSlider disappears completely.
Any comments/code snippets would be greatly appreciated.
Thanks,
Val

Answer 1

/* From: Java Tutorial - How To Use Layered Panes
*       LayeredPaneDemo.java
*       http://java.sun.com/docs/books/tutorial/uiswing/
*                                components/layeredpane.html
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.border.*;
public class valy extends JPanel implements ChangeListener {
  private SineWave sineWave = new SineWave();
  JSlider slider;
  JLayeredPane layeredPane;
  public valy() {
    slider = new JSlider(1, 30, 5);
    slider.setBounds(50,125,300,25);
    slider.addChangeListener(this);
    layeredPane = new JLayeredPane();
    layeredPane.setPreferredSize(new Dimension(400,300));
    layeredPane.setBorder(
      BorderFactory.createTitledBorder("Layered Pane App"));
    layeredPane.add(slider, JLayeredPane.PALETTE_LAYER);
    JPanel panel = new JPanel();
    panel.add(sineWave);
    JScrollPane scrollPane = new JScrollPane(panel);
    int width = layeredPane.getPreferredSize().width;
    int height = layeredPane.getPreferredSize().height;
    scrollPane.setBounds(15, 25, width - 30, height - 40);
    layeredPane.add(scrollPane, JLayeredPane.DEFAULT_LAYER);
    add(layeredPane);
  public void stateChanged(ChangeEvent e) {
    sineWave.setCycles(
      ((JSlider)e.getSource()).getValue());
  public static void main(String[] args) {
    JFrame frame = new JFrame();
    JComponent contentPane = new valy();
    contentPane.setOpaque(true);
    frame.setContentPane(contentPane);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setLocation(300,200);
    frame.setVisible(true);
/* From: Thinking in Java by Bruce Eckel
  *       3rd edition, Chapter 16
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class SineWave extends JLabel {
  private static int SCALEFACTOR = 200;
  private int cycles, points;
  private double[] sines;
  private int[] pts;
  public SineWave() {
    setCycles(5);
    setPreferredSize(new Dimension(400,400));
  public void setCycles(int newCycles) {
    cycles = newCycles;
    points = SCALEFACTOR * cycles * 2;
    sines = new double[points];
    for(int j = 0; j < points; j++) {
      double radians = (Math.PI/SCALEFACTOR) * j;
      sines[j] = Math.sin(radians);
    repaint();
  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D)g;
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                        RenderingHints.VALUE_ANTIALIAS_ON);   
    int maxWidth = getWidth();
    double hstep = (double)maxWidth/(double)points;
    int maxHeight = getHeight();
    pts = new int[points];
    for(int j = 0; j < points; j++)
      pts[j] =
        (int)(sines[j] * maxHeight/2 * .95 + maxHeight/2);
    g2.setPaint(Color.red);
    for(int j = 1; j < points; j++) {
      int x1 = (int)((j - 1) * hstep);
      int x2 = (int)(j * hstep);
      int y1 = pts[j - 1];
      int y2 = pts[j];
      g2.drawLine(x1, y1, x2, y2);
}