_sf = new XObject[_sf.length];
  public void reset()  {    _top = 0;    _linksTop = 0;    // Adding one here to the stack of frame positions will allow us always     // to look one under without having to check if we're at zero.    // (As long as the caller doesn't screw up link/unlink.)    _links[_linksTop++] = 0;  }