How to do equivalent of git-status using jgit?

I am making slow but steady progress thanks to all the help from the list. Thank you.

I need some guidance on how use jgit to determine what files have uncommitted changes in the local workspace and what is their status with respect to the GitIndex.

My goal is to implement a method with the following signature:

void commit(String commitMessage) {
  ...
}

I am looking at the doCommit method at:

<http://github.com/myabc/nbgit/tree/master/src/org/nbgit/util/GitCommand.java#L306>

This method takes a list of files. What I need is to somehow determine the list of files that need committing.

Thanks for your help.