jfeaturelib, java for glcm

Question

I am doing my program using jfeaturelib for searching glcm features. I am using this haralick.java and already run my program perfectly using this demo HaralickDemo.java. All I want to know is how to use horizontal neigbhor 0 degree only or 90 degree only. This is the code:

private void calculate() {
        calculateGreyValues();

        final int imageWidth = image.getWidth();
        final int imageHeight = image.getHeight();
        final int d = HARALICK_DIST;
        int i, j, pos;

        // image is not empty per default
        for (int y = 0; y < imageHeight; y++) {
            for (int x = 0; x < imageWidth; x++) {
                pos = imageWidth * y + x;

                // horizontal neighbor: 0 degrees
                i = x - d;
//                j = y;
                if (!(i < 0)) {
                    increment(grayValue[pos], grayValue[pos - d]);
                }

                // vertical neighbor: 90 degree
//                i = x;
                j = y - d;
                if (!(j < 0)) {
                    increment(grayValue[pos], grayValue[pos - d * imageWidth]);
                }

                // 45 degree diagonal neigbor
                i = x + d;
                j = y - d;
                if (i < imageWidth && !(j < 0)) {
                    increment(grayValue[pos], grayValue[pos + d - d * imageWidth]);
                }

                // 135 vertical neighbor
                i = x - d;
                j = y - d;
                if (!(i < 0) && !(j < 0)) {
                    increment(grayValue[pos], grayValue[pos - d - d * imageWidth]);
                }
            }
        }

And can you explain me detail of this haralick.java program?