ListAdapter.java

public void refreshMessages(ChatMessage message) {
        this.messages.add(message);
        notifyDataSetChanged();
    }

MainActivity.java

public void onMessageReceived(Message message) {
  runOnUiThread(new Runnable() {
     @Override
            public void run() {
            MListAdapter.refreshMessages(message);
            MListAdapter.notifyDataSetChanged();
            }
  });
}