Okay so you have downloaded. PasswdLevel4.class and have opened it up with the DJ Java Decompiler....
I was reading through the scripts and realized they werent going to put it in the script, I mean come on, this is level 4. That would have been a freebie. So what they have is this:
There actually is an infile method inside of the class and its function is to bring up a file and use it as a reference: thus we must search to file all instances of the word infile
Which brings us to this line:
infile = new String("level4");
meaning that a string has been created in the directory with the answer:
and what do you know at the URL
http://try2hack.nl/levels/level4
sits the file
Open up the file with notepad to see that it contains all information needed
??????:p is the username
??????:p is the password!