public void addField(String field,int orderNum,boolean descending){
  fields.add(new T2<>(field,orderNum));
  if (descending) {
    if (descendings == null)     descendings=new HashSet<>();
    descendings.add(field);
  }
}

public void addField ( String field , int orderNum , boolean descending ) { fields . add ( new T2 < > ( field , orderNum ) ) ; if ( descending ) { if ( descendings == null ) descendings = new HashSet < > ( ) ; descendings . add ( field ) ; } }
adds field to this index .
