private SortedMap < String , SortedSet < String > > findNamesPerSurname ( final String surname ) { if ( surnameIndex . containsKey ( surname ) ) { return surnameIndex . get ( surname ) ; } final SortedMap < String , SortedSet < String > > namesPerSurname = new TreeMap < String , SortedSet < String > > ( ) ; surnameIndex . put ( surname , namesPerSurname ) ; return namesPerSurname ; }
Find the map of full names to a sets of IDs for the given surname . If the surname is not already present create a new map and add it to the index .