class CitizenId implements Identity {

    protected int calculateCheckDigit() {
        int sum = 0;
        for (int position = 0; position < CitizenId.LENGTH - 1; position++) {
            sum += Character.digit(id.charAt(position), 10) * MULTIPLIER_TABLE[position];
        }
        int x = sum % 11;
        return (11 - x) % 10;
    }

    public  CitizenId(String id);

}