@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Draw2D draw2D = new Draw2D(this);
        setContentView(draw2D);
    }

public class Draw2D extends View {

    private Paint mPaint = new Paint();

    public Draw2D(Context context){
        super(context);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setColor(Color.WHITE);
        canvas.drawPaint(mPaint);
}