public Bookmark addBookmark(Bookmark bookmark){
  Assert.notNull(bookmark);
  bookmarks.add(bookmark);
  bookmark.setUser(this);
  return bookmark;
}

public Bookmark addBookmark ( Bookmark bookmark ) { Assert . notNull ( bookmark ) ; bookmarks . add ( bookmark ) ; bookmark . setUser ( this ) ; return bookmark ; }
a method to add bookmarks to user ' s list .
