accessing TrayIcon from another class

Question

) I have two classes, in the first (WoodyGui) I implemented the GUI, applied an ActionListener to the only JButton and added the TrayIcon to the SystemTray. By responding to the ActionEvent produced by the button I would like all elaboration to be made in the second class (WoodyEng), and once it's done I want it to display a notification on the TrayIcon. But how can I access the trayIcon from the second class? the error message I usually get is:

Exception in thread "Thread-2" java.lang.NullPointerException
  at WoodyEng.run(WoodyEng.java:27)
  at java.lang.Thread.run(Unknown Source)

any idea on what I'm missing? why can't I access the TrayIcon reference variabile from the second class like I do (i.e.) with the JButton? Thank you very much for any help...

import java.awt.*;
import java.awt.event.*;
import java.awt.SystemTray;
import java.awt.TrayIcon;
import javax.swing.*;

public class WoodyGui extends JFrame implements ActionListener {

  WoodyEng doer = new WoodyEng(this);

  JPanel area = new JPanel();
  JButton button = new JButton("GO!");

  // constructor
  public WoodyGui () {
    super("woody");
    setSize (150,200);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    button.addActionListener(doer);
    area.add(button);
    add(area);
    setVisible(true);

    if (SystemTray.isSupported()) {

    final TrayIcon trayIcon = new TrayIcon(new ImageIcon("icon.png", "").getImage(), "tray icon");
    final SystemTray tray = SystemTray.getSystemTray();

    try {
         tray.add(trayIcon);
         } catch (AWTException ex) {
                          System.out.println("TrayIcon could not be added.");
                                   }
    }
}

public static void main(String[] arguments) {
    WoodyGui pecker = new WoodyGui();
    }
}

here there's the second class:

import java.awt.event.*;
import java.awt.SystemTray;
import java.awt.TrayIcon;

  WoodyGui gui;
  Thread quack;

  public WoodyEng (WoodyGui in) {
    gui = in;
    }

  public void actionPerformed(ActionEvent eve) {
    Object who = eve.getSource();
    if (who == gui.button)
        {
        if (quack == null) {
            quack = new Thread(this);
            quack.start();
            }
        }
    }

public void run() {
    Thread thisThread = Thread.currentThread();
     while (quack == thisThread) {
     // all elaboration would occur here
     trayIcon.displayMessage("Woody","notification!!",TrayIcon.MessageType.INFO);
     if (quack != null) {
            quack = null; 
            }
     }
  }
}