如何让JWindow立即绘制

Question

How do I get a JWindow to immediately draw? In my example below there is a FULL 2 seconds between the window displaying and drawing as measured from the log output "done" to "painting jwindow". When the window is first displayed it is empty. Two seconds later, the image "splash-screen.png" is displayed.

I do not want to use the built-in splash screen support in Java. It has problems. Please, let's not get into that. I already spent days researching it... it doesn't work for my case (not fully described here).

I have run this code many times in succession to see if the delay is reduced... it remains at 2 seconds... very consistently. I'm running on macOS 10.14.1 and JDK 10.0.2.

Here is my SSCCE:

import java.util.logging.Logger;
import javax.swing.JWindow;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;
import javax.swing.ImageIcon;
import java.awt.Graphics;
import java.awt.BorderLayout;

public class MyApp {
    private final static Logger LOG = Logger.getLogger(MyApp.class.getName());
    public static void main(String args[]) throws Exception {
        final JWindow[] startupScreen = {null};
        SwingUtilities.invokeAndWait(() -> {
            try {
                Thread.currentThread().setPriority(10);
                LOG.info("edt thread priority: "+Thread.currentThread().getPriority());
                startupScreen[0] = new JWindow() {
                    @Override
                    public void paint(Graphics g) {
                        super.paint(g);
                        LOG.info("painting jwindow");
                    }
                };
                /*
                LOG.info("set layout");
                startupScreen[0].setLayout(new BorderLayout());
                */
                LOG.info("add splash image");
                startupScreen[0].add(
                    new JLabel(new ImageIcon(
                        MyApp.class.getResource("splash-screen.png")
                    )), BorderLayout.CENTER);
                LOG.info("pack");
                startupScreen[0].pack();
                LOG.info("set relative location");
                startupScreen[0].setLocationRelativeTo(null);
                LOG.info("set visible");
                startupScreen[0].setVisible(true);
                startupScreen[0].repaint();
                startupScreen[0].revalidate();
                LOG.info("done");
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        });
    }
}

Answer 1

Likely bottleneck:

startupScreen[0].add(new JLabel(new ImageIcon(
        MyApp.class.getResource("splash-screen.png"))), 
        BorderLayout.CENTER);

or more specifically, here:

MyApp.class.getResource("splash-screen.png")

as you're reading in an uncompressed and possibly large .png image resource. Solutions include not requiring the image or reading in a smaller compressed .jpg image.