sclass TranslucentWindowTest {
  new L<JWindow> windows;
  
  run {
    var screens = GraphicsEnvironment.getLocalGraphicsEnvironment().getScreenDevices();
    System.out.println("Detected " + screens.length + " screen(s)");
    for (int iScreen = 0; iScreen < screens.length; iScreen++) {
      var screen = screens[iScreen].getDefaultConfiguration().getBounds();
      
      // place window in center of screen
      new JWindow window;
      window.setBounds(
        screen.x+screen.width/4,
        screen.y+screen.height/4,
        screen.width/2,
        screen.height/2);
        
      // faint (mostly translucent) blue background
      window.setBackground(new Color(0, 0, 255, 64));
      
      window.setAlwaysOnTop(true);
      var label = new JLabel("Screen " + (iScreen+1) + " of " + screens.length);
      label.setHorizontalAlignment(JLabel.CENTER);
      window.add(label);
      window.setVisible(true);
      windows.add(window);
    }
      
    doAfter(10.0, r {
      disposeWindows(windows);
    });
  }
}

Began life as a copy of #1034002