银行卡卡号检验位

 public static char getValidateDigit(String number) {
  if(number== null || number.trim().length() == 0
                || !number.matches(" \\d+")) {
            throw new IllegalArgumentException("card no must be number!");
        }
        char[] chs = number.trim().toCharArray();
        int luhmSum = 0;
        for(int i = chs.length - 1, j = 0; i >= 0; i--, j++) {
            int k = chs[i] - '0';
            if(j % 2 == 0) {
                k *= 2;
                k = k / 10 + k % 10;
            }
            luhmSum += k;           
        }
        return (luhmSum % 10 == 0) ? '0' : (char)((10 - luhmSum % 10) + '0');
 }