Call repaint() from any class?

Question

I have a class where I have put a JButton. When I press the button I want to
call repaint() to update an Image object on a JPanel in a totally different class.
Unfortunately the Image object has to reside in the JPanel class and therefore I thought
I cound call an static method from the class with the JButton. Doesn't work.
Hence, how do I call repaint() for a JPanel from another class?

Answer 1

You can try comething like this ... quick and dirty (All caveats apply; use code at your own risk):
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
class BJCan  extends Canvas {
  private int width, height;
  private Color color;
  public BJCan() {
    setBackground(Color.black);
    color = Color.red;
  public void repaintCan(Color c) {
    color = c;
    repaint();
  public void paint(Graphics g) {
    width  = (int) getSize().getWidth();
    height = (int) getSize().getHeight();
    g.setColor(color);
    g.drawRect(10,10,width-20,height-20);
class BJPaintCan  extends JFrame {
  private int width, height;
  private JPanel bjp;
  private BJCan bjc;
  public BJPaintCan() {
    super("BJPaintCan");
    bjp = new JPanel();
    bjc = new BJCan();
    bjp.add(bjc);
    getContentPane().add(bjp);
    setBounds(50,50,300,300);
    width  = (int) getSize().getWidth();
    height = (int) getSize().getHeight();
    bjc.setSize(width-75, height-75);
    setVisible(true);
  public void repaint(Color c) {
    bjc.repaintCan(c);
public class BJPaint  extends JFrame {
  private boolean boo;
  private BJPaintCan bjpp;
  public BJPaint() {
    super("BJPaint");
    bjpp = new BJPaintCan();
    JButton hitIt = new JButton("Hit It!");
    hitIt.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ae) {
        if ( boo ) {
          bjpp.repaint(Color.blue);
          boo = false;
        else {
          bjpp.repaint(Color.yellow);
          boo = true;
    JPanel jp = new JPanel();
    jp.setLayout(new FlowLayout(FlowLayout.CENTER));
    jp.add(hitIt);
    getContentPane().add(jp);
    setBounds(375,255,300,200);
    setVisible(true);
  public static void main(String[] argv) {
    new BJPaint();
}~Bill