public void add(String uid){
  cleanIfNeeded();
  if (currentSet) {
    _idSet0.add(uid);
  }
 else {
    _idSet1.add(uid);
  }
}

public void add ( String uid ) { cleanIfNeeded ( ) ; if ( currentSet ) { _idSet0 . add ( uid ) ; } else { _idSet1 . add ( uid ) ; } }
adds a new uid
