对2个hex（16进制）字符串进行异或操作

private static String hexXOR(String hex1, String hex2){
    BigInteger i1 = new BigInteger(hex1, 16);
    BigInteger i2 = new BigInteger(hex2, 16);
    BigInteger res = i1.xor(i2);
    return res.toString(16).toUpperCase();
}

public static String xorHex(String a, String b) {
    char[] chars = new char[a.length()];
    for (int i = 0; i < chars.length; i++) {
        chars[i] = toHex(fromHex(a.charAt(i)) ^ fromHex(b.charAt(i)));
    }
    return new String(chars);
}

private static int fromHex(char c) {
    if (c >= '0' && c <= '9') {
        return c - '0';
    }
    if (c >= 'A' && c <= 'F') {
        return c - 'A' + 10;
    }
    if (c >= 'a' && c <= 'f') {
        return c - 'a' + 10;
    }
    throw new IllegalArgumentException();
}

private static char toHex(int nybble) {
    if (nybble < 0 || nybble > 15) {
        throw new IllegalArgumentException();
    }
    return "0123456789ABCDEF".charAt(nybble);
}