hough circle

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How can I get the number of circles that return by hough circle using java open CV.

Mat circles = new Mat();

Imgproc.HoughCircles(grayImage, circles, Imgproc.CV_HOUGH_GRADIENT, 1 , gray.rows()/2 , 200, 20, 30, 0 );

System.out.println("#rows " + circles.rows() + " #cols " + circles.cols());

I don't know how it store the circles in Mat that has cols and rows ??

I try to get the circle from column but it does not work !!!

if (circles.cols() > 0)
    for (int x = 0; x < circles.cols(); x++) 
    {
        double vCircle[] = circles.get(0,x);
        if (vCircle == null)
            break;
        Point pt = new Point(Math.round(vCircle[0]),
        Math.round(vCircle[1]));
        int radius = (int)Math.round(vCircle[2]);
        // draw the found circle
        Core.circle(imgRGB, pt, radius, new Scalar(0,255,0), 2);
        Core.circle(imgRGB, pt, 3, new Scalar(0,255,0), 2);
     }

For example look at this image

Any help please.