Java Security

hi,
I saw a little example of DigestInputStream in the Internet, I tested it using a text-file , read it using :

while(dis.read(buffer) > 0)
;

Then I called the digest method and afterwards called an toHexString() method. After that I called md5sum and calculated the checksum of the same text file, but the result was different.

1) Can that be possible ?
2) If yes, how ?

SO far,
strychnin1

here is the code (without exception handling etc.)

FileInputStream fis = new FileInputStream(filename);
DigestInputStream dis = new DigestInputStream(fis,md);

byte[] buffer = new byte[1024];

while(dis.read(buffer) > 0)
;

byte[] digest = md5.digest();

fis.close();

Then I called the tohexstring() method, but that method is correct and can't be the reason for it.