问如何用边界画出一条道路？

EN

public class SView extends View {

    Path path;
    Paint paint, paintWhite;
    RectF rf, rf2, rf3;

    public SView(Context context) {
        super(context);

        path = new Path();

        // 'paint' has a wider stroke-width 
        // compared to 'paintWhite' and 
        // thus becomes the border paint
        paint = new Paint();
        paint.setColor(Color.BLUE);
        paint.setAntiAlias(true);
        paint.setStrokeWidth(15);
        paint.setStyle(Style.STROKE);

        // 'paintWhite' colors the inner path
        paintWhite = new Paint();
        paintWhite.setColor(Color.WHITE);
        paintWhite.setAntiAlias(true);
        paintWhite.setStrokeWidth(12);
        paintWhite.setStyle(Style.STROKE);

        // For this example, we'll draw three
        // arcs bound by the following RectF
        // objects
        rf = new RectF(200, 200, 500, 500);
        rf2 = new RectF(200, 200, 400, 500);
        rf3 = new RectF(100, 200, 400, 500);                    
    }

    @Override
    protected void onDraw(Canvas canvas) {          

        // First arc bound by 'rf'
        path.arcTo(rf, 0, 180);

        // Draw 'path' using 'paint' 
        // and then, again using 'paintWhite'       
        canvas.drawPath(path, paint);
        canvas.drawPath(path, paintWhite);

        // Reset 'path' so as to clear 
        // history
        path.reset();

        // Repeat with the rest of arcs
        path.arcTo(rf2, 180, 180);      
        canvas.drawPath(path, paint);
        canvas.drawPath(path, paintWhite);      
        path.reset();           

        path.arcTo(rf3, 0, 180);            
        canvas.drawPath(path, paint);
        canvas.drawPath(path, paintWhite);  

    }       
}