code: public boolean pages_isFan(Long pageId, Integer userId)
      throws FacebookException, IOException {
      return extractBoolean(this.callMethod(FacebookMethod.PAGES_IS_FAN,
                                            new Pair<String,CharSequence>("page_id", pageId.toString()),
                                            new Pair<String,CharSequence>("uid", userId.toString())));
    }
docs: Checks whether a user is a fan of the page with the given <code>pageId</code>.
  @param pageId the ID of the page
  @param userId the ID of the user (defaults to the logged-in user if null)
  @return true if the user is a fan of the page
  @see <a href="http://wiki.developers.facebook.com/index.php/Pages.isFan">
  Developers Wiki: Pages.isFan</a>