public long numRecords() {
        if (numRecords == null) {
            try {
                numRecords = indexToKey.getNumRecords();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return numRecords;
    }
public long numRecords ( ) { if ( numRecords == null ) { try { numRecords = indexToKey . getNumRecords ( ) ; } catch ( IOException e ) { throw new RuntimeException ( e ) ; } } return numRecords ; }
Determine the total number of records in the map file, using the {@link IndexToKey} instance

@return  Total number of records and the map file