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  lt  output length  j              buf append hexDigit  output j   gt  gt  4   amp  0x0f            buf append hexDigit output j   amp  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

User · Accepted Answer

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:

User · Answer

That s because the byte   output is well  and array of bytes  you may think on it as an array of bytes representing each one an integer  but when you add them all into a single string you get something that is NOT an integer  that s why  You may either have it as an array of integers or try to create an instance of BigInteger

User · Answer

SHA-1 produces a 160-bit message  20 bytes   too large to be stored in an int or long value   As Ralph suggests  you could use BigInteger   To get a  less-secure  int hash  you could return the hash code of the returned byte array   Alternatively  if you don t really need SHA at all  you could just use the UUID s String hash code

User · Answer

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

User · Answer

you can use this method   https   stackoverflow com a 31804061 3343174 it s converting perfectly any hexadecimal number  presented as a string  to a decimal number

User · Answer

I finally find answers to my question based on all of your comments  Thanks  I tried this     public Integer calculateHash String uuid         try                          String hex   hexToString output             Integer i   Integer valueOf hex  16  intValue              Instead of using Integer  I used BigInteger and I returned the int value          BigInteger bi   new BigInteger hex  16           return bi intValue           catch  NoSuchAlgorithmException e            System out println  SHA1 not implemented in this system                         This solution is not optimal but I can continue with my project  Thanks again for your help

[java] Hexadecimal to Integer in Java

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