Android google v2 marker

Question

i have problem with google map v2 marker

so.. create marker on map works fine but... I after 12s change position and i want marken setPosition not to create new marker so my code

Timer timer = new Timer();
    timer.scheduleAtFixedRate(new TimerTask(){

        GetDataFromWeb GDFW = new GetDataFromWeb();

        public void run() {

            GDFW.doInBackground("a");
            GDFW.execute(); 

            for(int i = 0; i < GDFW.getList().size(); i++){

                lat = Double.valueOf(GDFW.getList().get(i).lat);
                log = Double.valueOf(GDFW.getList().get(i).lot);

                contactList.add(new LatLng(lat, log));

            }

                marker(m);  

        }

}, 12000, 12000);

i add in list lat and log when i create new marker on map

Runnable updateMarker = new Runnable() {

         GetDataFromWeb GDFW = new GetDataFromWeb();

            public void run() {

                 for (LatLng latLon : contactList) {

                        marker = map.addMarker(new MarkerOptions()
                            .position(latLon)
                            .title("Hello world")
                        );
                 }


             contactList.clear(); 

         }
     };
     handler.postDelayed(updateMarker, MARKER_UPDATE_INTERVAL);
    }

adter create marker how in marker setPostition? not clear all marker and create new