JWindow从while循环返回之前，JWindow不会重新绘制

Question

Assume I have a JWindow and a JFrame called TestWindow and TestFrame which should both be shown at the same time, why does the TestWindow only draw a blank grey window without its label while the TestFrame is inside the while(true)???

And why if I remove the while(true) the TestWindow correctly shows?

This is as example of a more complex program where I need to show a splashscreen while the main application is starting which takes 1 or 2 seconds. During this time the splashscreen should be shown regardless of the state of the main application, instead the splashscreen shows only when the main application is already finished, invokeAndWait doesn't actually wait for the splashscreen to be initialized.

TestFrame.java :

import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;

public class TestFrame extends JFrame
{
    public static void main(String args[])
    {
        try
        {
           SwingUtilities.invokeAndWait(new Runnable()
           {
               @Override
               public void run()
               {
                   new TestWindow();
               }
           });
        }
        catch (Exception ex)
       {
           Logger.getLogger(TestFrame.class.getName()).log(Level.SEVERE, null, ex);
       }
       SwingUtilities.invokeLater(new Runnable()
       {
           @Override
           public void run()
           {
               new TestFrame();
           }
        });
    }

    public TestFrame()
    {
        super("TestFrame");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        getContentPane().add(new JLabel("sss"), BorderLayout.CENTER);
        setSize(500, 120);
        setVisible(true);
        while(true)
        {
            //this makes the other not show
        }
    }
}

TestWindow.java :

import java.awt.BorderLayout;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JWindow;

public class TestWindow
{
    public TestWindow()
    {
        JWindow jWindow = new JWindow();
        JPanel contentPanel = new JPanel();
        final JLabel label = new JLabel("Test Window");
        contentPanel.add(label, BorderLayout.CENTER);
        jWindow.add(contentPanel);
        jWindow.setSize(300, 200);
        jWindow.setAlwaysOnTop(true);
        jWindow.setVisible(true);
    }
}

EDIT :

By the way, I realized putting a

catch (Exception ex)
        {
            Logger.getLogger(TestFrame.class.getName()).log(Level.SEVERE, null, ex);
        }
        try
        {
            Thread.sleep(1000);
        }

between the two TestWindow and TestFrame creation actually solves the problem, isn't there anything less hacky than this???

Answer 1

Your while (true) loop is being called on the Swing event dispatch thread, or EDT, tying it up and preventing this thread from doing its necessary actions including drawing all your GUI's and interacting with the user. The solution is simple -- 1) get rid of the while loop (as you already figured out), or 2) if the loop is absolutely necessary, do it in a background thread.

For more details on Swing threading, please check out Lesson: Concurrency in Swing .