Why setExtendedState(JFrame.ICONIFIED)does not work while windows screen locked?

all. i want to minimize my jframe with setExtendedState(JFrame.ICONIFIED), in most case, it works properly, but when it does not work when i lock my os(windows XP) screen with WIN+L.My wimple code are as follows:

import javax.swing.JDialog;
import javax.swing.JFrame;

public class FrameTest extends JFrame {
    public static FrameTest ft = new FrameTest();

    public static void main(String[] args)
    {
        FrameTest.ft.setVisible(true);
        FrameTest.ft.setLocation(300, 300);
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        JDialog dlg = new JDialog( ft, "xxx", true );
        ft.setExtendedState(JFrame.ICONIFIED);
        dlg.setVisible(true);//if not have this line, it works also in screen lock case 
    }开发者_JAVA技巧   
}

Any help will be appreciated.

---

It could me that you are manipulating Swing components from the main thread instead of the Event Dispatch Thread. Try wrapping the contents of main in:

public static void main(String[] args)
{
SwingUtilities.invokeLater(new Rennable() {
    @Override
    void run() {
        FrameTest.ft.setVisible(true);
        FrameTest.ft.setLocation(300, 300);
    }
    try {
        Thread.sleep(3000);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    SwingUtilities.invokeLater(new Rennable() {
        @Override
        void run() {
            JDialog dlg = new JDialog( ft, "xxx", true );
            ft.setExtendedState(JFrame.ICONIFIED);
            dlg.setVisible(true);case 
     }   
}

If that doesn't help, try splitting the second invokeLater block into:

    SwingUtilities.invokeLater(new Rennable() {
        @Override
        void run() {
            ft.setExtendedState(JFrame.ICONIFIED);
     }   
    SwingUtilities.invokeLater(new Rennable() {
        @Override
        void run() {
            JDialog dlg = new JDialog( ft, "xxx", true );
            dlg.setVisible(true);case 
     }   

That gives Swing a chance to respond to the iconification before handing off control to the dialog.