Question

The issue is that i get extra 2 elements in listOf_sorted_APPFiles from somewhere.

    Map<String, List<APPfile>> APPfilesMapByFileName 
            = new HashMap<String, List<APPfile>>();

       ...

    Collections.sort(fileNames, String.CASE_INSENSITIVE_ORDER);
    logger.debug("Sorted count " + fileNames.size()); // 77

    // There will always be a list. Most of the time it will contains 
    // 1 element, but sometimes it may contains more

    for (String sortedFileName : fileNames) {
        for (APPfile a: APPfilesMapByFileName.get(sortedFileName)) {
               listOf_sorted_APPFiles.add(a);
        }
    }

    logger.debug("listOf_sorted_APPfiles count: " + 
                listOf_sorted_APPfiles.size()); // 79
       ...

I expect counts of listOf_sorted_APPFiles and fileNames to match, yet somehow i get extra 2 elements. Elements that are added extra are the ones coming from lists that contain more then one element.

Answer 1

You have two nested “for”. So, if sometimes there happen more than one element of APPfilesMapByFileName with the same filename, you MUST have more output elements.