notificationlistener

Does anyone know of a good tutorial for beginners on how to create an interface with a notification listener that listens to a class and how to observe it from another class?

I have a class called ODSLoader that I need to listen to - I have the basic structure of the interface (I think) but I have no idea how to code it to actually listen to ODSLoader.

public interface Notifier {
         public interface NotificationListener {
             public void onNotificationPosted();           
            
         }

         public void addListener(NotificationListener listener);
         public void removeListener(NotificationListener listener);
      }

I then have another class with a progress bar that needs to be notified when to progress but I have no idea how to do that either...

This is my progress bar

            progressBar = new JProgressBar(0,100);
            progressBar.setValue(0);
            springLayout.putConstraint(SpringLayout.NORTH, progressBar, 12, SpringLayout.SOUTH, btnProcess);
            springLayout.putConstraint(SpringLayout.WEST, progressBar, 10, SpringLayout.WEST, frame.getContentPane());
            springLayout.putConstraint(SpringLayout.EAST, progressBar, -10, SpringLayout.EAST, frame.getContentPane());
            frame.getContentPane().add(progressBar);

Can anyone point me in the right direction or show me how to code it?
Thanks