@Override public int hashCode(){
  final int prime=31;
  int result=(operation == null) ? 0 : operation.hashCode();
  result+=prime * ((text == null) ? 0 : text.hashCode());
  return result;
}

@ Override public int hashCode ( ) { final int prime = 31 ; int result = ( operation == null ) ? 0 : operation . hashCode ( ) ; result += prime * ( ( text == null ) ? 0 : text . hashCode ( ) ) ; return result ; }
create a numeric hash value for a diff . this function is not used by dmp .
