sclass WindowDragger extends MouseAdapter {
  MouseEvent mouseDownEvent;
  Pt rel;
  Window window;
  
  *(MouseEvent *mouseDownEvent, Window *window) {
    rel = pt(
      mouseDownEvent.getXOnScreen()-window.getX(),
      mouseDownEvent.getXOnScreen()-window.getY());
  }

  public void mouseDragged(MouseEvent e) {
    updatePosition(e);
  }
  
  public void mouseReleased(MouseEvent e) {
    if (e.getButton() != mouseDownEvent.getButton()) ret;
    updatePosition(e);
    removeMouseAdapter(window, this);
    dragDone();
  }
  
  void updatePosition(MouseEvent e) {
    window.setLocation(
      e.getXOnScreen()-rel.x,
      e.getYOnScreen()-rel.y);
  }
  
  void dragDone {}
}