private GoogleMap mMap;
MarkerOptions options;
BitmapDescriptor icon;
MarkerOptions mop;
LatLng trainLocation;
Double latitu,longitu;

    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;

////         Add a marker in Sydney and move the camera
        trainLocation = new LatLng(latitu,longitu);

        mop = new MarkerOptions();
        mop.position(trainLocation);
        mop.title("Me");
        mop.icon(icon);
        mMap.addMarker(mop);

        mMap.moveCamera(CameraUpdateFactory.newLatLng(trainLocation));
        mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(trainLocation,13f));
    }

DatabaseReference myRef;
myRef = FirebaseDatabase.getInstance().getReference().child("location");
myRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        latitu = (Double) dataSnapshot.child("lat").getValue();
        longitu = (Double) dataSnapshot.child("lon").getValue();

        Log.d("LatLon",latitu+longitu+"");
        Toast.makeText(LiveTrain.this, latitu.toString()+" - "+longitu.toString(), Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});