// TODO: sometimes they can't be closed anymore? (see #1014939)
sclass FrameCoActivator {
  long lastTime;
  int timeout = 100; // prohibit endless loop
  
  *(final Frame... frames) {
    for (final Frame f1 : frames) {
      f1.addWindowListener(new WindowAdapter {
        public void windowIconified(WindowEvent e) {
          lastTime = sysNow();
        }
        
        public void windowActivated(WindowEvent e) {
          if (sysNow() >= lastTime+timeout) {
            lastTime = sysNow();
            //print(text);
            for (Frame f2 : frames)
              if (f2 != f1)
                activateFrame(f2);
            activateFrame(f1);
          }
        }
      });
    }
  }
}

static Frame[] coActivateFrames(Frame... frames) {
  new FrameCoActivator(frames);
  ret frames;
}

static <A extends Frame> L<A> coActivateFrames(L<A> frames) {
  coActivateFrames(toArray(frames, Frame.class));
  ret frames;
}