Validates a South African ID number

validate SA ID.java

    /**
     * Validates a South African ID number
     *
     * See http://geekswithblogs.net/willemf/archive/2005/10/30/58561.aspx and
     * https://www.westerncape.gov.za/general-publication/decoding-your-south-african-id-number-0
     *
     * @param id
     * @return
     */
    public static boolean validId(String id) {
        Matcher m = ID_PATTERN.matcher(id);
        if(!m.find())
            return false;
        int yy = Integer.parseInt(m.group(1));
        int mm = Integer.parseInt(m.group(2));
        int dd = Integer.parseInt(m.group(3));
        int g = Integer.parseInt(m.group(4));
        int s = Integer.parseInt(m.group(5));
        int c = Integer.parseInt(m.group(6));
        int a = Integer.parseInt(m.group(7));
        int z = Integer.parseInt(m.group(8));

        if(mm < 1 || mm > 12 || dd < 1 || dd > 31) return false;

        char [] cs = id.toCharArray();
        int s1 = (cs[0] - '0') + (cs[2] - '0') + (cs[4] - '0') + (cs[6] - '0') + (cs[8] - '0') + (cs[10] - '0');
        int s2 = Integer.parseInt("" + cs[1] + cs[3] + cs[5] + cs[7] + cs[9] + cs[11]);
        s2 *= 2;
        char [] cx = Integer.toString(s2).toCharArray();
        s2 = 0;
        for(char cc : cx)
            s2 += cc - '0';
        s2 += s1;
        String st = Integer.toString(s2);
        s2 = st.charAt(st.length() - 1) - '0';

        if(10 - s2 != z) return false;

        // System.out.println(yy + "-" + mm + "-" + dd + " " + (g >= 5 ? 'M' : 'F') + " " + s + " " + (c == 0 ? "citizen" : "other") + " " + a + " " + z );

        return true;
    }
    private static final Pattern ID_PATTERN = Pattern.compile("^(\\d{2})(\\d{2})(\\d{2})(\\d)(\\d{3})([01])(\\d)(\\d)$");