Re: convert byte array to hex string using BigInteger

From:

Joerg Meier <joergmmeier@arcor.de>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 22 Jun 2013 00:26:49 +0200

Message-ID:

<qdnytcrvwob4.14l9nuassw2g5$.dlg@40tude.net>

On Fri, 21 Jun 2013 14:51:09 -0700, Roedy Green wrote:

On Thu, 20 Jun 2013 14:03:21 +0200, Laura Schmidt <ls@mailinator.com>
wrote, quoted or indirectly quoted someone who said :

Here is a low level direct way to convert byte[] to a hex String. It
should be quite a bit faster than using high level routines.

/**
* Fast convert a byte array to a hex string
* with possible leading zero.
* @param b array of bytes to convert to string
* @return hex representation, two chars per byte.
*/
public static String toHexString ( byte[] b )
   {
   StringBuilder sb = new StringBuilder( b.length * 2 );
   for ( int i=0; i<b.length; i++ )
      {
      // look up high nibble char
      sb.append( hexChar [( b[i] & 0xf0 ) >>> 4] );

      // look up low nibble char
      sb.append( hexChar [b[i] & 0x0f] );
      }
   return sb.toString();
   }

Note that this is pretty much a copy and paste version of the converter
that already comes with the JRE:

from javax.xml.bind.DatatypeConverterImpl:

public String printHexBinary(byte[] data) {
         StringBuilder r = new StringBuilder(data.length * 2);
         for (byte b : data) {
             r.append(hexCode[(b >> 4) & 0xF]);
             r.append(hexCode[(b & 0xF)]);
         }
         return r.toString();
     }

For a reason I was unable to discern it was actually a teensy bit slower
than the Oracle implementation.

Liebe Gruesse,
        Joerg

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