luk knap i titelbar

Ikke med en JFrame, men men en JWindow kan muligvis benyttes. Bemærk dog:
It does not have the title bar, window-management buttons, or other trimmings associated with a JFrame, but it is still a "first-class citizen" of the user's desktop, and can exist anywhere on it.

http://java.sun.com/j2se/1.4/docs/api/javax/swing/JWindow.html

et eksempel ville være rart

import javax.swing.*;

public class WindowTest extends JWindow
{
    private int frameWidth = 640;
    private int frameHeight = 480;
    private JLabel label;
   
    public WindowTest()
    {
        label = new JLabel("Hello World");
        this.getContentPane().add(label);
       
        //Center Window
        java.awt.Dimension screenSize = java.awt.Toolkit.getDefaultToolkit().getScreenSize();
        setSize(new java.awt.Dimension(frameWidth, frameHeight));
        setLocation((screenSize.width - this.getWidth()) / 2, (screenSize.height - this.getHeight()) / 2);
    }
}

class Main
{
    public static void main(String args[])
    {
          new WindowTest().show();
    }
}

Læg iøvrigt mærke til at der ikke findes et entry i taskbaren.

Hejsa c",)

Hvis du vil fjerne titel baren, kan du bruge metoden: setUndecorated(boolean)
Du kan læse om den her: http://java.sun.com/j2se/1.4.1/docs/api/java/awt/Frame.html#setUndecorated(boolean)

Du har ret!
Jeg prøvede lige at modificere et eksempel jeg havde liggende:
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;

public class MyFrame extends JFrame implements WindowListener, Runnable, ActionListener
{

    private int frameWidth = 640;
    private int frameHeight = 480;
    private JScrollPane jsp;
    private JTextArea jta;
    private JButton jb;
    private Thread thread;

    public MyFrame()
    {
        createFrame();
    }

    private void createFrame()
    {
        setTitle("MyFrame");
        setUndecorated(true);
        setResizable(false);
        addWindowListener(this);   

        //Place components here:
        jta = new JTextArea();
        jsp = new JScrollPane(jta);
        this.getContentPane().add(jsp, BorderLayout.CENTER);

        jb = new JButton("Hello");
        jb.addActionListener(this);
        this.getContentPane().add(jb, BorderLayout.SOUTH);
       
        //Center Frame
        java.awt.Dimension screenSize = java.awt.Toolkit.getDefaultToolkit().getScreenSize();
        setSize(new java.awt.Dimension(frameWidth, frameHeight));
        setLocation( (screenSize.width-this.getWidth()) / 2, (screenSize.height - this.getHeight()) / 2);
    }
   
    public void run()
    {
        while(true)
        {
            jta.append("Hello World" + System.getProperty("line.separator"));
            try
            {
                thread.sleep(100);
            }
            catch(Exception e)
            {
                e.printStackTrace();
            }
        }
    }
   
    public void actionPerformed(ActionEvent e)
    {
        Object source = e.getSource();
        if(source == jb)
        {
            thread = new Thread(this);
            thread.start();
        }
    }

    public void windowOpened(WindowEvent e){}
    public void windowClosing(WindowEvent e){ endProgram();}
    public void windowClosed(WindowEvent e){}
    public void windowIconified(WindowEvent e){}
    public void windowDeiconified(WindowEvent e){}
    public void windowActivated(WindowEvent e){}
    public void windowDeactivated(WindowEvent e){}

    public void endProgram()
    {
        dispose();
        System.exit(0);
    }
}

class Main
{
    public static void main(String args[])
    {
          new MyFrame().show();
    }
}

Det er en smart metode, jeg synes bare ens JFrame bliver så grim af det... c",)