Convert HexString to Big Integer

String reverse ="D7821A727982782A";
String sAuthoCode ="";

BigInteger bi_try = new BigInteger(reverse, 16);
BigInteger bi_autho = new BigInteger(sAuthoCode, 16);
BigInteger bi_pref = new BigInteger("AB7",16);

BigInteger bi_result;
bi_result= bi_pref.add(bi_try).add(bi_autho).subtract(bi_subf);