How to reach a method of an object from within another class

Question

I am stuck in a situation with my program. The current situation is as follows:
1- There is a class in which I draw images. This class is an extension of JPanel
2- And there is a main class (the one that has main method) which is an extension of JFrame
3- In the main class a create an instance(object) of StatusBar class and add it to the main class
4- I also add to the main class an instance of image drawing class I mentioned in item 1 above.
5- In the image drawing class i define mousemove method and as the mouse
moves over the image, i want to display some info on the status bar
6- How can do it?
7- Thanks!

Answer 1

It would make sense that the panel not be forced to understand its context (in this case a JFrame, but perhaps an applet or something else later on) but offer a means of tracking.
class DrawingPanel extends JPanel {
  HashSet listeners = new HashSet();
  public void addDrawingListener(DrawingListener l) {
     listeners.add(l);
  protected void fireMouseMove(MouseEvent me) {
     Iterator i = listeners.iterator();
     while (i.hasNext()) {
        ((DrawingListener) i.next()).mouseMoved(me.getX(),me.getY());
class Main implements DrawingListener {
  JFrame frame;
  JLabel status;
  DrawingPanel panel;
  private void init() {
     panel.addDrawingListener(this);
  public void mouseMoved(int x,int y) {
     status.setText("x : " + x + " y: " + y);
public interface DrawingListener {
  void mouseMoved(int x,int y);
}Of course you could always just have the Main class add a MouseMotionListener to the DrawingPanel, but if the DrawingPanel has a scale or gets embedded in a scroll pane and there is some virtual coordinate transformation (not using screen coordinates) then the Main class would have to know about how to do the transformation. This way, the DrawingPanel can encapsulate that knowledge and the Main class simply provides a means to listen to the DrawingPanel. By using a DrawingListener, you could add other methods as well (versus using only a MouseMotionListener).
Obviously, lots of code is missing above. In general, its not a good idea to extend JFrame unless you really are changing the JFrames behavior by overrding methods, etc. Extending JPanel is okay, as you are presumably modifiying the drawing code, but you'd be better off extending JComponent.