code: public void grantMembership(Collection<? extends Jid> jids) throws XMPPErrorException, NoResponseException, NotConnectedException, InterruptedException {
          changeAffiliationByAdmin(jids, MUCAffiliation.member);
      }
docs: Grants membership to other users. Only administrators are able to grant membership. A user
  that becomes a room member will be able to enter a room of type Members-Only (i.e. a room
  that a user cannot enter without being on the member list).
  
  @param jids the XMPP user IDs of the users to grant membership.
  @throws XMPPErrorException if an error occurs granting membership to a user.
  @throws NoResponseException if there was no response from the server.
  @throws NotConnectedException
  @throws InterruptedException