Java by API/java.beans/VetoableChangeListener

implements VetoableChangeListener

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 MainClass {
  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);
    
    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"); 
    }
  }
}