Validation for Singapore NRIC and FIN number

nric-validation.java

/**
 * Validates Singapore NRIC / FIN in 2 stages:
 * 1) Ensure first letter starts with S, T, F or G and the last letter is A-Z
 * 2) Calculate weight of digits in between first and last character of the input string,
 * determine what the last letter should be, then match it against the last character of the
 * input string.
 *
 * @param inputString NRIC / FIN string to be validated
 * @return true if NRIC/FIN passes, false otherwise
 */
public static boolean validateNric(String inputString) {
    String nricToTest = inputString.toUpperCase();

    // first letter must start with S, T, F or G. Last letter must be A - Z
    if (!Pattern.compile("^[STFG]\\d{7}[A-Z]$").matcher(nricToTest).matches()) {
        return false;
    } else {
        char[] icArray = new char[9];
        char[] st = "JZIHGFEDCBA".toCharArray();
        char[] fg = "XWUTRQPNMLK".toCharArray();

        for (int i = 0; i < 9; i++) {
            icArray[i] = nricToTest.charAt(i);
        }

        // calculate weight of positions 1 to 7
        int weight = (Integer.parseInt(String.valueOf(icArray[1]), 10)) * 2 + 
                (Integer.parseInt(String.valueOf(icArray[2]), 10)) * 7 +
                (Integer.parseInt(String.valueOf(icArray[3]), 10)) * 6 +
                (Integer.parseInt(String.valueOf(icArray[4]), 10)) * 5 +
                (Integer.parseInt(String.valueOf(icArray[5]), 10)) * 4 +
                (Integer.parseInt(String.valueOf(icArray[6]), 10)) * 3 +
                (Integer.parseInt(String.valueOf(icArray[7]), 10)) * 2;

        int offset = icArray[0] == 'T' || icArray[0] == 'G' ? 4 : 0;

        int lastCharPosition = (offset + weight) % 11;

        if (icArray[0] == 'S' || icArray[0] == 'T') {
            return icArray[8] == st[lastCharPosition];
        } else if (icArray[0] == 'F' || icArray[0] == 'G') {
            return icArray[8] == fg[lastCharPosition];
        } else {
            return false; // this line should never reached due to regex above
        }
    }
}