class Article {
        public String id;
        public String cover;
        public String title;
        public String digest;
        public String url;
        public boolean rr;

        public Article() {
        }

        public Article(String id, String cover, String title, String digest, String url, boolean rr) {
            this.id = id;
            this.cover = cover;
            this.title = title;
            this.digest = digest;
            this.url = url;
            this.rr = rr;
        }
    }
    public Article top;
    public List<Article> subArticles;

    public ArticleContent() {
    }

    public ArticleContent(String id, String cover, String title, String digest, String url, boolean rr) {
        this.top = new Article(id, cover, title, digest, url, rr);
    }

    public ArticleContent addSubArticle(String id, String cover, String title, String digest, String url, boolean rr)  {<FILL_FUNCTION_BODY>

        if (subArticles == null)
            subArticles = new ArrayList<>();
        subArticles.add(new Article(id, cover, title, digest, url, rr));
        return this;
    
<no_super_class>