java 16进制求和

  
public String makeChecksum(String hexdata) {
    if (hexdata == null || hexdata.equals("")) {
        return "00";
    }
    hexdata = hexdata.replaceAll(" ", "");
    int total = 0;
    int len = hexdata.length();
    if (len % 2 != 0) {
        return "00";
    }
    int num = 0;
    while (num < len) {
        String s = hexdata.substring(num, num + 2);
        total += Integer.parseInt(s, 16);
        num = num + 2;
    }
    return hexInt(total);
}

private String hexInt(int total) {
    int a = total / 256;
    int b = total % 256;
    if (a > 255) {
        return hexInt(a) + format(b);
    }
    return format(a) + format(b);
}

private String format(int hex) {
    String hexa = Integer.toHexString(hex);
    int len = hexa.length();
    if (len < 2) {
        hexa = "0" + hexa;
    }
    return hexa;
}

依次得出16进制的和