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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 !!

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