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 !!

Answer 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)