Help with google-api-java-client

I'm trying to parse a youtube video feed, and for each video print the list of its thumbnails. I've tried something like that:

 public static class VideoFeed {
    @Key List<Video> items;
  }

  public static clas开发者_运维百科s Video {
    @Key String title;
    @Key String description;
    @Key DateTime uploaded;
    @Key Player player;
    @Key Thumbnail thumbnail;
  }

  public static class Player {
    @Key("default") String defaultUrl;
  }



  public static class Thumbnail{

    List<Thumb> items = new ArrayList<Thumb>();
  }

  public static class Thumb extends GenericJson{
      @Key("default") String defaultUrl;
      @Key Integer height;
      @Key Integer width;
      @Key String time;

  }

and print it

for (Video video : feed.items) {
  System.out.println();
  System.out.println("Video title: " + video.title);
  System.out.println("Uploaded: " + video.uploaded);
  System.out.println("URL: " + video.player.defaultUrl);

  Thumbnail thumbnails = video.thumbnail;
  for (Thumb thumb : thumbnails.items){

      System.out.println("Thumbnail: "+thumb.defaultUrl);
  }

}

But the thumbnails don't get printed.

What's the problem?

Is it because you are missing the @Key annotation on the Thumbnail.items?