Android gravity sensing

public class HelloanActivity extends Activity implements View.OnClickListener,SensorEventListener{ImageView imageView = null;private SensorManager mSensorManager = null;      private Sensor mSensor = null;     private float x,y,z;    private Handler handler = new Handler(){public void handleMessage(Message msg) {super.handleMessage(msg);}};public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        findViewById(R.id.main_button).setOnClickListener(this);        imageView = (ImageView)findViewById(R.id.main_image);        mSensorManager = (SensorManager)this.getSystemService(SENSOR_SERVICE);                mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);        mSensorManager.registerListener(this, mSensor, SensorManager.SENSOR_DELAY_NORMAL);    }@Overridepublic void finish() {super.finish();mSensorManager.unregisterListener(this);}@Overridepublic void onAccuracyChanged(Sensor sensor, int accuracy) {}@Overridepublic void onSensorChanged(SensorEvent event) {x = event.values[SensorManager.DATA_X];y = event.values[SensorManager.DATA_Y];z = event.values[SensorManager.DATA_Z];}      public void onClick(View v)     {       System.out.println("x="+x);       System.out.println("y="+y);       System.out.println("z="+z);    }                }