public final class ByteArrayWrapper
{
private final byte[] contents;
public ByteArrayWrapper(byte[] contents)
{
this.contents = contents;
}
public byte[] getContents()
{
return contents;
}
public int hashCode()
{
int result = 0;
int pos = 0;
for (int i=contents.length-1; i>=0; i--)
{
result += (contents[i] << pos);
pos = (pos + 8) % 32;
}
return result;
}
// this is 10x as slow as the other hashCode
public int hashCodeSlow()
{
StringBuffer buf = new StringBuffer(contents.length*3);
for (int i=contents.length-1; i>=0; i--)
{
buf.append(contents[i]);
}
return buf.toString().hashCode();
}
public boolean equals(Object obj)
{
try
{
ByteArrayWrapper other = (ByteArrayWrapper)obj;
if (contents.length != other.contents.length) return false;
for (int i=contents.length-1; i>=0; i--)
{
if (contents[i] != other.contents[i]) return false;
}
return true;
}
catch(NullPointerException ex)
{
return false;
}
catch(ClassCastException ex)
{
return false;
}
}
public static void main(String[] args)
{
ByteArrayWrapper baw1 = new ByteArrayWrapper(
new byte[] {1, 2, 3, 5, 1, 77, 125, 10, 11});
ByteArrayWrapper baw2 = new ByteArrayWrapper(
new byte[] {1, 2, 3, 5, 1, 77, 125, 10, 11});
if (baw1.equals(baw2)) System.out.println("The two arrays are equal");
if (baw2.equals(baw1)) System.out.println("The two arrays are equal");
System.out.println("baw1.hashCode()=" + baw1.hashCode());
System.out.println("baw2.hashCode()=" + baw2.hashCode());
final int NUMBER_HASHCODE_TESTS = 100000;
long start = System.currentTimeMillis();
for (int i=0; i<NUMBER_HASHCODE_TESTS; i++)
{
baw1.hashCode();
}
System.out.println("It took " + (System.currentTimeMillis()-start) +
"ms to call hashCode " + NUMBER_HASHCODE_TESTS + " times");
}
}
-----Original Message-----
From: Rickard �berg [mailto:[EMAIL PROTECTED]]
Sent: 11 August 2000 06:59
To: jBoss Developer
Subject: Re: [jBoss-Dev] [newbie] byte[].hashcode()
Hey
marc fleury wrote:
> did you know that
>
> byte[] byte1 = {1,2,3};
> byte[] byte2 = {1,2,3};
>
> yields
> byte1.equals(byte2) = false;
> and
> byte1.hashCode() != byte2.hashCode();
Of course.. since you are comparing the arrays, and not their contents.
Both equals and hashCode will be the Object defaults, which work on
memory adress of the actual object.
> blows my mind man....
>
> what is the best way to compute a byte[].hashCode()?
Iterate and add the elements together. Also depends on the distribution
of the contents. Why do you need a byte array BTW? Is this for the Xid?
Why not use an enumerated long or something?
/Rickard
--
Rickard �berg
Email: [EMAIL PROTECTED]
http://www.telkel.com
http://www.jboss.org
http://www.dreambean.com
