@Override public int hashCode(){
  int result=dataType != null ? dataType.hashCode() : 0;
  result=31 * result + (data != null ? data.hashCode() : 0);
  return result;
}

@ Override public int hashCode ( ) { int result = dataType != null ? dataType . hashCode ( ) : 0 ; result = 31 * result + ( data != null ? data . hashCode ( ) : 0 ) ; return result ; }
generate a hash based on the string representations of both data and datatype .
