private boolean isTracked(File file, Repository repo) throws IOException {
		ObjectId objectId = repo.resolve(Constants.HEAD);
		RevTree tree;
		if (objectId != null)
			tree = new RevWalk(repo).parseTree(objectId);
		else
			tree = null;

		TreeWalk treeWalk = new TreeWalk(repo);
		treeWalk.setRecursive(true);
		if (tree != null)
			treeWalk.addTree(tree);
		else
			treeWalk.addTree(new EmptyTreeIterator());
		treeWalk.addTree(new DirCacheIterator(repo.readDirCache()));
		treeWalk.setFilter(PathFilterGroup.createFromStrings(Collections.singleton(
				Repository.stripWorkDir(repo.getWorkTree(), file))));
		return treeWalk.next();

	}

how to check if a file is shared with a git repo?

RemoveCommand#isTracked

Java