Re: convert byte array to hex string using BigInteger

From:

rossum <rossum48@coldmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 20 Jun 2013 15:44:58 +0100

Message-ID:

<9q46s811lpb47jnqv1mtct778r7nnelju4@4ax.com>

On Thu, 20 Jun 2013 15:32:56 +0200, Laura Schmidt <ls@mailinator.com>
wrote:

On 06/20/2013 03:09 PM, rossum wrote:

This is a case of RTFM. The Javadocs for BigInteger(byte[]) tell you
that it expects the byte array in two's complement representation, so
a leading 1 bit is interpreted as a negative number. You need a
different constructor:

public BigInteger(int signum, byte[] magnitude)

You are right, sorry.

Now I get a hex string without sign. But now the decode method does not
return the original bytes anymore:

private byte [] hex_decode (String val)
{
  BigInteger b = new BigInteger (val,16);
  byte [] t = b.toByteArray();

  return (t);
}

There is no other constructor for byte arrays.
And I don't really understand why it doesn't return the original byte array.

Laura

Again, you need to look at the Javadoc. That tells you toByteArray()
returns the two's complement representation of the BigInt.

Either convert the two's complement or write your own hex_decode(), it
isn't that difficult.

As a minor point, you should follow the Java naming conventions:
hexEncode() and hexDecode(). Underscores are more C++ than Java.

rossum