Questions[estructuras-de-datos]

My problem is the following:

I have a .csv file in which the attributes of an object are stored, which are: CP, Street, number, neighborhood, recipient I want to order these attributes based on the CP with the following code:

public class ExternalSort{

static int N = 2000000; /** size of the file in disk */
static int M = 100000;  /** max items the memory buffer can hold */

public static void externalSort(String fileName)
{
    String tfile = "temp-file-";
    int[] buffer = new int[M < N ? M : N];

    try
    {
        FileReader fr = new FileReader(fileName);
        BufferedReader br = new BufferedReader(fr);
        int slices = (int) Math.ceil((double) N/M);

        int i, j;
        i = j = 0;
        /** Iterar a través de los elementos del archivo */
        for (i = 0; i < slices; i++)
        {
            /** Leer fragmentos de M-elementos a la vez desde el archivo */
            for (j = 0; j < (M < N ? M : N); j++)
            {
                String t = br.readLine();
                if (t != null)
                    buffer[j] = Integer.parseInt(t.substring(0,4));
                else
                    break;
            }
            /** Sort M elementos */
            Arrays.sort(buffer);

            /** Escriba los números ordenados en el archivo temporal */
            FileWriter fw = new FileWriter(tfile + Integer.toString(i) + ".txt");
            PrintWriter pw = new PrintWriter(fw);
            for (int k = 0; k < j; k++)
                pw.println(buffer[k]);

            pw.close();
            fw.close();
        }

        br.close();
        fr.close();

        /** Ahora abra cada archivo y combinelos, luego vuelva a escribirlos en el disco */
        int[] topNums = new int[slices];
        BufferedReader[] brs = new BufferedReader[slices];

        for (i = 0; i < slices; i++)
        {
            brs[i] = new BufferedReader(new FileReader(tfile + Integer.toString(i) + ".txt"));
            String t = brs[i].readLine();
            if (t != null)
                topNums[i] = Integer.parseInt(t);
            else
                topNums[i] = Integer.MAX_VALUE;
        }

        FileWriter fw = new FileWriter("external-sorted.txt");
        PrintWriter pw = new PrintWriter(fw);

        for (i = 0; i < N; i++)
        {
            int min = topNums[0];
            int minFile = 0;

            for (j = 0; j < slices; j++)
            {
                if (min > topNums[j])
                {
                    min = topNums[j];
                    minFile = j;
                }
            }

            pw.println(min);
            String t = brs[minFile].readLine();
            if (t != null)
                topNums[minFile] = Integer.parseInt(t);
                else
                topNums[minFile] = Integer.MAX_VALUE;
        }
        for (i = 0; i < slices; i++)
            brs[i].close();

        pw.close();
        fw.close();
    } catch (FileNotFoundException e)
    {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch(NullPointerException ex){
        ex.printStackTrace();
    } 
}


static String generateInput(int n)
{
    String fileName = "external-sort.txt";
    Random rand = new Random();

    try
    {
        FileWriter fw = new FileWriter(fileName);
        PrintWriter pw = new PrintWriter(fw);

        for (int i = 0; i < n; i++)
            pw.println(rand.nextInt(9900) + 100);

        pw.close();
    }
    catch (IOException e)
    {
        e.printStackTrace();
    }

    return fileName;
}

It is supposed to return the file ordered based on the CP but it doesn't.

As an example I have the following data:

68148, Sur, 45, Real Casa Blanca (Residential), Juan Gabriel Contreras Caceres

68010, Sur, 57, Elsa (Subdivision), Tomas Prieto Jurado

68045, East, 144, Star (Cologne), Jorge Conde Prieto

And the ordered file should be like this:

68010, Sur, 57, Elsa (Subdivision), Tomas Prieto Jurado

68045, East, 144, Star (Cologne), Jorge Conde Prieto

68148, Sur, 45, Real Casa Blanca (Residential), Juan Gabriel Contreras Caceres