public class Juego extends SurfaceView implements View.OnTouchListener{

private Paint paint;
int radio = 100, x = 100, y = 100;

public Juego(Context context, AttributeSet attrs) {
    super(context, attrs);
    this.setOnTouchListener(this);
    setFocusable(true);
    paint = new Paint();
}

public void onDraw(Canvas canvas) {

    paint.setColor(Color.WHITE);
    canvas.drawRect(0, 0, getWidth(), getHeight(), paint);

    paint.setColor(Color.BLACK);
    canvas.drawCircle(x, y, radio, paint);

    invalidate();
}

  @Override
  public boolean onTouch(View view,MotionEvent motionEvent){

    x = (int)motionEvent.getX();
    y = (int)motionEvent.getY();

    invalidate();
    return true;
  }
}