public JavaFileObject getFileObject(RelativeDirectory subdirectory, String file) {
        RelativeFile fullZipFileName = new RelativeFile(subdirectory, file);
        ZipFileIndex.Entry entry = zfIndex.getZipIndexEntry(fullZipFileName);
        JavaFileObject ret = new ZipFileIndexFileObject(fileManager, zfIndex, entry, zfIndex.getZipFile());
        return ret;
    }