// ImagePanel, the class which must provide the BufferedImage to listeners.
public class ImagePanel extends JPanel implements Lookup.Provider {
    private BufferedImage m_Image;

    ...

    private InstanceContent m_Content;
    private Lookup m_Lookup;

    public ImagePanel(EditorTopComponent comp) {
        m_TopComponent = comp;

        m_Content = new InstanceContent();
        m_Lookup = new AbstractLookup(m_Content);
    }

    @Override
    public Lookup getLookup() {
        return m_Lookup;
    }

    public void setImage(BufferedImage image) {
        m_Image = image;
        m_Content.add(m_Image);
    }

    ...
}



// ImageTab, the class that needs the image as soon as it is set.
// In the constructor of that class (ImageTab is created after ImagePanel is, but BEFORE the image is set in ImagePanel)
final Lookup.Result temp = m_ImagePanel.getLookup().lookupResult(BufferedImage.class);
        temp.addLookupListener(new LookupListener() {
            @Override
            public void resultChanged(LookupEvent ev) {
                ImageTab.this.resultChanged(temp);
            }
        });
        resultChanged(temp);
...
public void resultChanged(Lookup.Result result) {
        Logger.getLogger(getClass().getName()).info("Something changed: " + result.toString());
    }


// Output
Something changed: org.openide.util.lookup.AbstractLookup$R@2fdcf09f for Lookup.Template[type=class java.awt.image.BufferedImage,id=null,instance=null]
Something changed: org.openide.util.lookup.AbstractLookup$R@74ed4eb6 for Lookup.Template[type=class java.awt.image.BufferedImage,id=null,instance=null]
Something changed: org.openide.util.lookup.AbstractLookup$R@34490808 for Lookup.Template[type=class java.awt.image.BufferedImage,id=null,instance=null]
Something changed: org.openide.util.lookup.AbstractLookup$R@34490808 for Lookup.Template[type=class java.awt.image.BufferedImage,id=null,instance=null]