@Override public String stringValue(){
  if (fieldsData instanceof String || fieldsData instanceof Number) {
    return fieldsData.toString();
  }
 else {
    return null;
  }
}

@ Override public String stringValue ( ) { if ( fieldsData instanceof String || fieldsData instanceof Number ) { return fieldsData . toString ( ) ; } else { return null ; } }
the value of the field as a string , or null . if null , the reader value or binary value is used . exactly one of stringvalue ( ) , readervalue ( ) , and binaryvalue ( ) must be set .
