android - Google maps Pushpin Error -

i want show particular location on map , on perticular location want put pushpin notification. have tried below code showing nullpointer exception please me add markers.

public class mapdemoactivity extends mapactivity {  mapview mapview;   mapcontroller mc;  geopoint p;  class mapoverlay extends com.google.android.maps.overlay     {         @override         public boolean draw(canvas canvas, mapview mapview,          boolean shadow, long when)          {             super.draw(canvas, mapview, shadow);                                 //---translate geopoint screen pixels---             point screenpts = new point();             mapview.getprojection().topixels(p, screenpts);              //---add marker---             bitmap bmp = bitmapfactory.decoderesource(                 getresources(), r.drawable.pushpin);                         canvas.drawbitmap(bmp, screenpts.x, screenpts.y-50, null);                      return true;         }     }    public void oncreate(bundle savedinstancestate)     {         super.oncreate(savedinstancestate);         setcontentview(r.layout.main);          mapview = (mapview) findviewbyid(r.id.mapview);          mapview.setbuiltinzoomcontrols(true);         mc.animateto(p);         mc.setzoom(17);           //---add location marker---         mapoverlay mapoverlay = new mapoverlay();         list<overlay> listofoverlays = mapview.getoverlays();         listofoverlays.clear();         listofoverlays.add(mapoverlay);                  mapview.invalidate();      } @override protected boolean isroutedisplayed() {     // todo auto-generated method stub     return false; } 

this link may useful you

https://github.com/commonsguy/cw-advandroid/tree/master/maps/nooyawktouch/