Java Beans VetoableChangeListener handle vetoable changed event

import java.awt.BorderLayout;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyVetoException;
import java.beans.VetoableChangeListener;

import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JInternalFrame;

public class Main {

  public static void main(final String args[]) {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JDesktopPane desktop = new JDesktopPane();

    JInternalFrame palette = new JInternalFrame("Palette", true, true, true, true);

    palette.addVetoableChangeListener(new IconPolice());

    palette.setBounds(350, 150, 100, 100);
    desktop.add(palette, JDesktopPane.PALETTE_LAYER);
    palette.setVisible(true);/*  ww w. j  av  a2  s  .  c  om*/

    frame.add(desktop, BorderLayout.CENTER);
    frame.setSize(500, 300);
    frame.setVisible(true);
  }
}

class IconPolice implements VetoableChangeListener {
  public void vetoableChange(PropertyChangeEvent ev) throws PropertyVetoException {
    String name = ev.getPropertyName();
    if (name.equals(JInternalFrame.IS_ICON_PROPERTY) && (ev.getNewValue() == Boolean.TRUE)) {
      System.out.println("JInternalFrame.IS_ICON_PROPERTY");
    }
  }
}