Hexadecimal to Integer in Java

Question

I am trying to convert a String hexadecimal to an integer. The string hexadecimal was calculated from a hash function (sha-1). I get this error : java.lang.NumberFormatException. I guess it doesn't like the String representation of the hexadecimal. How can I achieve that. Here is my code :

public Integer calculateHash(String uuid) {

    try {
        MessageDigest digest = MessageDigest.getInstance("SHA1");
        digest.update(uuid.getBytes());
        byte[] output = digest.digest();

        String hex = hexToString(output);
        Integer i = Integer.parseInt(hex,16);
        return i;           

    } catch (NoSuchAlgorithmException e) {
        System.out.println("SHA1 not implemented in this system");
    }

    return null;
}   

private String hexToString(byte[] output) {
    char hexDigit[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
            'A', 'B', 'C', 'D', 'E', 'F' };
    StringBuffer buf = new StringBuffer();
    for (int j = 0; j < output.length; j++) {
        buf.append(hexDigit[(output[j] >> 4) & 0x0f]);
        buf.append(hexDigit[output[j] & 0x0f]);
    }
    return buf.toString();

}

For example, when I pass this string : _DTOWsHJbEeC6VuzWPawcLA, his hash his : 0xC934E5D372B2AB6D0A50B9F0341A00ED029BDC15

But i get : java.lang.NumberFormatException: For input string: "0xC934E5D372B2AB6D0A50B9F0341A00ED029BDC15"

I really need to do this. I have a collection of elements identified by their UUID which are string. I will have to store those elements but my restrictions is to use an integer as their id. It is why I calculate the hash of the parameter given and then I convert to an int. Maybe I am doing this wrong but can someone gives me an advice to achieve that correctly!!

Thanks for your help !!

Solution 1

Why do you not use the java functionality for that:

If your numbers are small (smaller than yours) you could use: Integer.parseInt(hex, 16) to convert a Hex - String into an integer.

  String hex = "ff"
  int value = Integer.parseInt(hex, 16);  

For big numbers like yours, use public BigInteger(String val, int radix)

  BigInteger value = new BigInteger(hex, 16);

@See JavaDoc:

• Integer.parseInt(String value, int radix)
• BigInteger(String value, int radix)

Solution 2

Try this

public static long Hextonumber(String hexval)
    {
        hexval="0x"+hexval;
//      String decimal="0x00000bb9";
        Long number = Long.decode(hexval);
//.......       System.out.println("String [" + hexval + "] = " + number);
        return number;
        //3001
    }

Comments

[OscarRyz]

I really don't get this answer, isn't that what he's already trying in Integer i = Integer.parseInt(hex,16);?

[Dimitri]

I tried to use the UUID's String hash code but I get also IllegalArgumentException. This is why I drop UUID; By the way, I don't even know how they generate their UUID, it is not my project

[Dimitri]

Is it possible to convert from BigInteger to Integer?

[Michael Brewer-Davis]

By "UUID's String hash code" I mean uuid.hashCode() (which uses the function String.hashCode()). I can't see that giving an IAE?

[Java Drinker]

Additionally get rid of the 0x part... I don't know that this is allowed.. and if you can guarantee that it will always be 0xABC982.., then you can always just remove the first 2 chars

[eggyal]

I think you mean to instantiate a new BigInteger in your third line of code? It also ought to be more efficient to construct directly from the byte array rather than the hexadecimal string representation.

[Dimitri]

Yeah, i know. I just tried this method. But the problem is when I try String id = UUID.fromString(uuid) i get an IllegalArgumentException.

[OscarRyz]

Only if the value of BigInteger is not larger than Integer.MAX_VALUE which in this case it will be. See: download.oracle.com/javase/6/docs/api/java/math/…

[user207421]

This answer is basically meaningless. An array of bytes is simply a multiple-precision number. Doesn't answer the question.

[Ralph]

@eggyal: You are right, it is new BigInteger - I have corrected it