OpenCV HoughLine only detect one line in image

I am following the docs/tutorial of openCV to detect lines in image. However, I only got one out of the four similar lines in the image. Here is the result

And here is my code:

Mat im = Imgcodecs.imread("C:/Users/valer/eclipse-workspace/thesis-application/StartHere/resource/4 lines.JPG");
    
    Mat gray = new Mat(im.rows(), im.cols(), CvType.CV_8SC1);
    
    Imgproc.cvtColor(im, gray, Imgproc.COLOR_RGB2GRAY);

    Imgproc.Canny(gray, gray, 50, 150);
    
    Mat lines = new Mat();

    Imgproc.HoughLines(gray, lines, 1, Math.PI/180, 200);

    for (int i = 0; i < lines.cols(); i++){
        double data[] = lines.get(0, i);
        double rho = data[0];
        double theta = data[1];
        double cosTheta = Math.cos(theta);
        double sinTheta = Math.sin(theta);
        double x0 = cosTheta * rho;
        double y0 = sinTheta * rho;
        Point pt1 = new Point(x0 + 10000 * (-sinTheta), y0 + 10000 * cosTheta);
        Point pt2 = new Point(x0 - 10000 * (-sinTheta), y0 - 10000 * cosTheta);
        Imgproc.line(im, pt1, pt2, new Scalar(0, 0, 200), 3);
    }
    Imgcodecs.imwrite("C:/Users/valer/eclipse-workspace/thesis-application/StartHere/resource/process/line_output.jpg", im);

I have tried playing around with the parameters for threshold, but I kept getting same (and sometimes worst) results. Would anyone please point out where am I doing wrong?

In the lines matrix result, lines are stored by row, not by column. So lines.rows() gives you line count and you can iterate with lines.get(i, 0) to fetch each line.