if (impl == null) throw new SocketException ("Not connected");
if (isClosed()) throw new SocketException("ServerSocket is closed");
  public void setReceiveBufferSize (int size)    throws SocketException  {    if (impl == null)      throw new SocketException ("Not connected");    if (size <= 0)      throw new IllegalArgumentException ("SO_RCVBUF value must be > 0");    impl.setOption (SocketOptions.SO_RCVBUF, new Integer (size));  }