Trigger TrayIcon Popup From Another Class

I have created a swing application which has a TrayIcon, this has one button that has the following code:

displayItem.addActionListener(
new ActionListener(){
public void actionPerformed(ActionEvent e) {
trayIcon.displayMessage("Hello Title","Hello World", TrayIcon.MessageType.WARNING);
}
});
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I have another class which I run via the following:

Thread counter = new Thread(new regCheck());
counter.start();

And within this "start" method I want to be able to wait 10 seconds and then trigger the popup that appeared within the original class. I think that the right method of achieving this is to create a function within my original class causes the popup.

public void display(String a, String b) {
trayIcon.displayMessage(a,b, TrayIcon.MessageType.WARNING);
}

However I have two issues here:

-firstly I dont know how to get the original trayIcon image from the method it was initialized into this new method.
-secondly I dont know how to trigger this event from the other class. Here is the method that I tried (but doesnt work)

window w = new window();
w.display("a","b");

This doesn't work because window's main begins to run and endlessly creates multiple windows and TrayIcons. What is the correct way to implement this sort of behaviour?