You are probably in for a tough time. The index format is not well 
documented, and it may be platform dependent.  I suggest you
debug the swish program (in C) on your target platform and watch
as it creates (not searches) the index to give you a better idea of
what is stored in there, and it what order. Then debug swish while
doing a search to see how it jumps into and around the index file.
This is pretty low-level stuff but since you intend to write your own
search in Java you will need to know what the search process 
looks like in a painfully detailed way anyway.

At 07:44 AM 5/3/99 -0700, Massimo Andriotto wrote:
>Hello,
>I'm a student and I need of your help, please.
>I'm trying to translate the C code of a SWISH.
>In my thesis I must search in a index generated by SWISH.
>The problem is that I need to do this from a Java application, I must to do
>it in Java because I'm trying to realize a mobile agent that perform a
>search; I must use Java Serialization to move the searcher.
>Does anybody can help me to understand the internal structure of Swish index
>?
>Excuse me for my english and thanks a lot for you time.
>
>Massimo Andriotto
>