("Only one of putFields and defaultWriteObject may be called, and it may only be called once");
("Only one of writeFields and defaultWriteObject may be called, and it may only be called once");
  private void markFieldsWritten() throws IOException  {    if (currentObject == null || currentObjectStreamClass == null)      throw new NotActiveException	("defaultWriteObject called by non-active class and/or object");    if (fieldsAlreadyWritten)      throw new IOException	("Only one of putFields and defaultWriteObject may be called, and it may only be called once");    fieldsAlreadyWritten = true;  }