static int centerArrangeWindows_spacing = 20;

static L<Window> centerArrangeWindows(final Window... windows) {
  swing {
    int w = centerArrangeWindows_spacing*(l(windows)-1);
    for (Window win : windows) w += win.getWidth();
    int x = (screenWidth()-w)/2;
    for (Window win : windows) {
      setFrameLocation(win, x, (screenHeight()-win.getHeight())/2);
      x += win.getWidth() + centerArrangeWindows_spacing;
    }
  }
  ret asList(windows);
}