مشکل در پروژه شمارشگر معکوش

سلام 

به نظر خودم عینا کد ها مثل استاد نوشته شده ولی کرش میکنه مال من : 

اکتیویتی اصلی :

public class ActivityCounter extends Activity {

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        TextView txtCount = (TextView) findViewById(R.id.txtCount);
        ThreadCounter threadcounter = new ThreadCounter();
        threadcounter.setSecond(20);
        threadcounter.settextView(txtCount);
        threadcounter.start();

    }
}

 thread counter : 

public class ThreadCounter extends Thread {

    private int      second;
    private int      counter;
    private TextView textview;


    public void setSecond(int value) {
        second = value;
        counter = second;

    }


    @Override
    public void run() {
        super.run();
        while (counter > 0) {
            try {
                Thread.sleep(1000);
            }
            catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            counter--;
            if (textview != null) {

                G.HANDLER.post(new Runnable() {

                    @Override
                    public void run() {
                        textview.setText(counter);

                    }
                });

            }

            Log.i("LOG", " cOUNTER is" + counter);

        }
    }


    public void settextView(TextView value) {
        textview = value;
    }

}




g class : 

public class G extends Application {

    public static Context       context;
    public static final Handler HANDLER = new Handler();


    @Override
    public void onCreate() {
        super.onCreate();
        context = getApplicationContext();
    }
}