Help me with Presence of Participants in MUC?

I knew I can get Presence of User in MUC with the following codes:

  MUCUser user = (MUCUser) presence.getExtension("x","http://jabber.org/protocol/muc#user");

if (user != null) {

MUCUser.Item item = user.getItem();

if (item != null) {

System.out.println(item.getJid() + “:” + item.getAffiliation() + “:” + item.getRole());

}

}

Actually, I need to get Presence of Participants with the function:

public void joined(String user){}

Please tell me how to get Presence of Participant in joined(String user)

Thanks in advance!

MultiUserChat#getOccupant(MultiUserChat#getRoom() + “/” + user)