Open recent files in NBP. Why 2 times messages ?

Dear List

Following to Geert-Jan, I did some coding relate to Opening recent *txt files in NB Platform, as followed by:
http://wiki.netbeans.org/DevFaqListenForOpenEvents [Or see the last part].

It works, but , when I used a System.out.println("Opened " + fe.getFile()... to show the details of the process,
I understood that, it works for two time!

Similarly, when I opened a non *txt file like *jpg it also shows ERROR messages (JOptionPane.showMessageDialog(null, "Unsupported format: Please . . .) for two times!!

Hope someone can answer this behaviour.

Thanks in advance

K


//==== The installer class & its use in MainTopComponent.... ======

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package org.myorg.googletoolbar;

/**
 *
 * @author user
 */
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.HashSet;
import javax.swing.JOptionPane;
import org.openide.awt.StatusDisplayer;
import org.openide.filesystems.FileChangeAdapter;
import org.openide.filesystems.FileEvent;
import org.openide.filesystems.FileObject;
import org.openide.loaders.DataObject;
import org.openide.windows.OnShowing;
import org.openide.windows.TopComponent;
import org.openide.windows.WindowManager;

@OnShowing
public class Installer implements Runnable {
    @Override
    public void run() {
WindowManager.getDefault().getRegistry().addPropertyChangeListener(new PropertyChangeListener() {
            @Override
            public void propertyChange(PropertyChangeEvent evt) {
                if (evt.getPropertyName().equals("opened")) {
                    HashSet<TopComponent> newHashSet = (HashSet<TopComponent>) evt.getNewValue();
                    HashSet<TopComponent> oldHashSet = (HashSet<TopComponent>) evt.getOldValue();
                    for (TopComponent topComponent : newHashSet) {
                        if (!oldHashSet.contains(topComponent)) {
                            DataObject dObj = topComponent.getLookup().lookup(DataObject.class);
                            if (dObj != null) {
                                FileObject currentFile = dObj.getPrimaryFile();
                                if (currentFile != null && currentFile.getNameExt().endsWith(".xyz") /*&& currentFile.getMIMEType().equals("text/x-java")*/ ) {
StatusDisplayer.getDefault().setStatusText("Hurray 111! " + "Opened " + currentFile.getPath().toString(), 1);
System.out.println("Opened " + currentFile.getNameExt());

 //if(currentFile.getNameExt().endsWith(".xyz") || currentFile.getNameExt().endsWith(".gen"))
 //   { JOptionPane.showMessageDialog(null, "Unsupported format: Please use *.xyz , *.gen , or dftb_in.hsd", "Error", JOptionPane.ERROR_MESSAGE);}

currentFile.addFileChangeListener(new FileChangeAdapter() {
                                        @Override
                                        public void fileChanged(FileEvent fe) {
StatusDisplayer.getDefault().setStatusText("Hurray! 222 " + "Saved " + fe.getFile().getNameExt(), 1);
System.out.println("Opened " + fe.getFile().getNameExt());
                                        }
                                    });
                                } else { JOptionPane.showMessageDialog(null, "Unsupported format: Please use *.xyz , *.gen , or dftb_in.hsd", "Error", JOptionPane.ERROR_MESSAGE);}

                            }
                        }
                    }
                }
            }
        });
    }

} 
====================  in the <TopComponent.Java>  =======

...

// get open file info
        Installer pp = new Installer();
        pp.run();
...