We have the visitFileFailed method and the body is below. Considering that it only add the argument to the List and then returns skip subtree, where does the check for failure take place? I don't understand. Shouldn't there be an if clause somewhere? ex. if file could not be accessed then add to filed list. else skip. 
failed.add(file.toString());
    return FileVisitResult.SKIP_SUBTREE;
public class Solution extends SimpleFileVisitor<Path> {
    public static void main(String[] args) throws IOException {
        EnumSet<FileVisitOption> options = EnumSet.of(FileVisitOption.FOLLOW_LINKS);
        final Solution solution = new Solution();
        Files.walkFileTree(Paths.get("D:/"), options, 20, solution);

        List<String> result = solution.getArchived();
        System.out.println("All archived files:");
        for (String path : result) {
            System.out.println("\t" + path);
        }

        List<String> failed = solution.getFailed();
        System.out.println("All failed files:");
        for (String path : failed) {
            System.out.println("\t" + path);
        }
    }

    private List<String> archived = new ArrayList<>();
    private List<String> failed = new ArrayList<>();

    public List<String> getArchived() {
        return archived;
    }

    public List<String> getFailed() {
        return failed;
    }

    @Override
    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
        if (file.toString().endsWith(".rar") || file.toString().endsWith(".zip"))
            archived.add(file.toString());
        return super.visitFile(file, attrs);
    }

    @Override
    public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
        failed.add(file.toString());
        return FileVisitResult.SKIP_SUBTREE;
    }
}