java cumulative and checksum implementation is recommended in hexadecimal of

Given 1 string, find the hexadecimal sum of the string, given 1 string and the checksum code, whether the checksum and the sum are legal, say nothing more directly on the code

public static String makeChecksum(String data) {
 if (data == null || data.equals("")) {
  return "";
 }
 int total = 0;
 int len = data.length();
 int num = 0;
 while (num < len) {
  String s = data.substring(num, num + 2);
  System.out.println(s);
  total += Integer.parseInt(s, 16);
  num = num + 2;
 }
 /**
  *  with 256 The largest of these is 255 , i.e., 16 Into the system FF
  */
 int mod = total % 256;
 String hex = Integer.toHexString(mod);
 len = hex.length();
 //  If the length of the check bit is not enough, make up 0, This is a two-digit check 
 if (len < 2) {
  hex = "0" + hex;
 }
 return hex;
 }