Ytukyg

I wrote a function:

    private static LinearFunction aproxFunction(List<Point> list) {

    try{

        int amountOfClusters = getAmountOfClusters(list);

        //System.out.println(amountOfClusters); for debug

        LinearFunction linear = new LinearFunction[amountOfClusters];

        int clusters = new int[amountOfClusters][2]; // 2nd field 0 == r, 1 == g, 2 == b

        clusters = getClusters(list, amountOfClusters);

        for(int i = 0; i < amountOfClusters; i++) {

            List<Point> pointsList = new ArrayList<>(getPointsInCluster(list, clusters[i][0], convertIdToString(clusters[i][1])));

            int points = new int[pointsList.size()][3];

            for(int j = 0; j < points.length; j++) {

                points[j][0] = pointsList.get(j).getX();

                points[j][1] = pointsList.get(j).getY();

                points[j][2] = pointsList.get(j).getValue();

            }

            pointsToFile(pointsList, clusters[i][0],  convertIdToString(clusters[i][1]), "_points_in_cluster_"); 

            int array = new int[2][2];

            array = aprox(removeDuplicates(points));

            if((array[1][0] - array[0][0]) == 0) {

                linear[i].a = 0;

                linear[i].b = 0;

                linear[i].flag = true;

                linear[i].c = array[0][0];

            } else {

                linear[i].a = (array[1][1] - array[0][1]) / (array[1][0] - array[0][0]);

                linear[i].b = array[1][1] - array[1][0] * linear[i].a;

            }

            linear[i].cluster = clusters[i][0];

            linear[i].id = convertIdToString(clusters[i][1]);   

        }

        return linear;

    } catch (Exception e) {

        System.out.println("Error - aproxFunction: " + e.getMessage());

    }

    LinearFunction error = new LinearFunction[1];

    error[0].a = -1;

    return error;

}

and I constantly receive the error messages of either division by null or just null. I can't find the reason for that.
The only division in this function happens here:

linear[i].a = (array[1][1] - array[0][1]) / (array[1][0] - array[0][0]);

but above that you have a check for null division, so how can I still get that error message.

As for the error message null I just don't know what it means. I read that it might be caused by an objects being null but how to find out which and where?

You are initialising an array of LinearFunctions, but you are not initialising each LinearFunction object inside it.

Have you tried this:

private static LinearFunction aproxFunction(List<Point> list) {

try{

    int amountOfClusters = getAmountOfClusters(list);

    //System.out.println(amountOfClusters); for debug

    LinearFunction linear = new LinearFunction[amountOfClusters];

    int clusters = new int[amountOfClusters][2]; // 2nd field 0 == r, 1 == g, 2 == b

    clusters = getClusters(list, amountOfClusters);

    for(int i = 0; i < amountOfClusters; i++) {

        linear[i] = new LinearFunction()

        ...

I solved this NullPointerException like this:

            for(int i = 0; i < amountOfClusters; i++) {

            LinearFunction lf = new LinearFunction();

            List<Point> pointsList = new ArrayList<>(getPointsInCluster(list, clusters[i][0], convertIdToString(clusters[i][1])));

            int points = new int[pointsList.size()][3];

            for(int j = 0; j < points.length; j++) {

                points[j][0] = pointsList.get(j).getX();

                points[j][1] = pointsList.get(j).getY();

                points[j][2] = pointsList.get(j).getValue();

            }

            pointsToFile(pointsList, clusters[i][0],  convertIdToString(clusters[i][1]), "_points_in_cluster_"); 

            int array = new int[2][2];

            array = aprox(removeDuplicates(points));

            if((array[1][0] - array[0][0]) == 0) {

                lf.a = 0;

                lf.b = 0;

                lf.flag = true;

                lf.c = array[0][0];

            } else {

                lf.a = (array[1][1] - array[0][1]) / (array[1][0] - array[0][0]);

                lf.b = array[1][1] - array[1][0] * linear[i].a;

            }

            lf.cluster = clusters[i][0];

            lf.id = convertIdToString(clusters[i][1]);

            linear[i] = lf;

        }

So I created an object of the same class as the array, and only at the end of the loop I point it to an element of the array.