Here is the code
Iterator i = MultiUserChat.getJoinedRooms(connectionManager.getXMPPConnection(), "test123@dulanjaya-pc");
while(i.hasNext()) {
System.out.println(i.next());
}
Figured out. Need to put the service as /Smack
Iterator i = MultiUserChat.getJoinedRooms(connectionManager.getXMPPConnection(), "test123@dulanjaya-pc/Smack");