MD5 hash differs in Java and PHP

I really need halp getting the Java MD5 and PHP MD5 yield the same result.

In PHP I simply use thins: md5($string);

In Java I use this:
try {
                  
                  //get
                  hash = snStr+authStr;
                  byte defaultBytes[] = hash.getBytes();
                  MessageDigest algorithm = MessageDigest.getInstance("MD5");
                  algorithm.reset();
                  algorithm.update(defaultBytes);
                  byte messageDigest[] = algorithm.digest();

                  StringBuffer hexString = new StringBuffer();
                  for (byte aMessageDigest : messageDigest) {
                    // We need to pad small values with an extra zero: http://forum.de.selfhtml.org/archiv/2005/10/t117779/
                    int val = 0xff & aMessageDigest;
                    if (val < 16)
                      hexString.append("0");
                    hexString.append(Integer.toHexString(val));
                  }
                  hash = hexString.toString();
            } catch (NoSuchAlgorithmException nsae) {
                  nsae.printStackTrace();
            }


I have also tried withouth the padding.

The even more strange thing is that for short strings the two MD5:s are the same but if the string to be hashed are longer than around 10 chars I will get two different results

Thank you very much for your help!