if (container != parent) throw new AWTError("BoxLayout can't be shared");
  public void invalidateLayout(Container parent)  {    synchronized (container.getTreeLock())      {    xChildren = null;    yChildren = null;    xTotal = null;    yTotal = null;    offsetsX = null;    offsetsY = null;    spansX = null;    spansY = null;  }  }