question: public HubLinkMapping ( String fileName , int numberOfHubs , Network network ) { this . numberOfHubs = numberOfHubs ; if ( fileName . contains ( ".mappingTable." ) ) { readMappingTable ( fileName ) ; unMappedLinksAtZeroHub = true ; return ; } handleUnmappedLinksStart ( ) ; try { FileReader fr = new FileReader ( fileName ) ; BufferedReader br = new BufferedReader ( fr ) ; String line ; StringTokenizer tokenizer ; String token ; int linkId ; line = br . readLine ( ) ; while ( line != null ) { tokenizer = new StringTokenizer ( line ) ; for ( int i = 0 ; i < this . numberOfHubs ; i ++ ) { token = tokenizer . nextToken ( ) ; linkId = ( int ) Double . parseDouble ( token ) ; linkHubMapping . put ( Integer . toString ( linkId ) , i ) ; } if ( tokenizer . hasMoreTokens ( ) ) { throw new RuntimeException ( "the number of hubs is wrong" ) ; } line = br . readLine ( ) ; } } catch ( RuntimeException e ) { throw e ; } catch ( Exception e ) { throw new RuntimeException ( "Error reading the hub link mapping file" ) ; } linkHubMapping . remove ( "-1" ) ; handleUnmappedLinksEnd ( network ) ; }
target:  reads the mappings from the file. The file has columns (first column for first hub and all the links corresponding to that hub below it) 