Suggesting a text change:

We read:

We’ve registered a WatchService to observe any change to the current directory.

but what actually happens is

We’ve registered a path with a filesystem WatchService to get told about ‘modification’ changes to the current directory.

On my system, file deletion does not give rise to a notification, but creation does (probably because after creation, the file is additionally modified)

The text

"Report any file changed within next 1 minute..."

should really say

System.out.println("Report the first change on '" + path + "' within the next 1 minute...");

Note that the code given uses an inner loop. At this point, I really feel we should use collect():

if(watchKey != null) {
   watchKey.pollEvents()
      .stream()
      .forEach(event ->
         System.out.println(event.context()));
}

Nicer:

String res = (watchKey == null) ? "nothing happened at all!" :
                        watchKey.pollEvents()
                                .stream()
                                .map(event -> event.context().toString())
                                .collect(Collectors.joining(", "));

As I had some trouble understanding how the WatchService actually works and what those keys are doing, here is the full method

    public void watchFileChange() throws IOException {
        final Path path = Paths.get(theDir);
        String res;
        // Try-with-resources to close the WatchService at the end
        // (and thus cancel all the WatchKeys registered with it)
        try (WatchService watchService = path.getFileSystem().newWatchService()) {
            try {
                // No need to retain the WatchKey returned by path.register()
                path.register(watchService, StandardWatchEventKinds.ENTRY_MODIFY);
                System.out.println("Report the first change on '" + path + "' within the next 1 minute...");
                WatchKey watchKey = null;
                // poll() "Retrieves and removes the next watch key, waiting if necessary up to
                // the specified wait time if none are yet present."
                try {
                    watchKey = watchService.poll(1, TimeUnit.MINUTES);
                } catch (InterruptedException ex) {
                    System.out.println("Got interrupted");
                }
                res = (watchKey == null) ? "nothing happened at all!" :
                        watchKey.pollEvents()
                                .stream()
                                .map(event -> event.context().toString())
                                .collect(Collectors.joining(", "));
            } catch (NoSuchFileException ex) {
                res = "Looks like there is no filesystem entry '" + path + "'";
            }
        }
        System.out.println(res);
    }