correct syntax to return a 2D array from a method

Question

The below two methods(sortRows and sortColumns) are supposed to return a 2D array of rList and cList, but I believe I am declaring it wrong .

At the bottom of the main where I try to print it; the array is not returned to the main method.

In the main:

rList and cList cannot be resolved to a variable.

public class Markov {
    public static void main(String[] args) {

        double[][] matrix = new double[3][3];

        int r, c;
        double val;
        String inputV;

        // asks user for values
        for (c = 0; c < 3; c++)
            for (r = 0; r < 3; r++) {
                inputV = JOptionPane.showInputDialog("Enter value for row # "   + (r + 1) + " , column # " + (c + 1));
                val = Double.parseDouble(inputV);
                matrix[c][r] = val;
        }
        if (ValidateMarkov(matrix) == false) {
            System.out.println(" Invalid Markov, values must be postive, colummn values must sum to 1.0 ");
        } else {
            System.out.println("Valid Markov");
        }

        SortRows(matrix);
        SortColumns(matrix);

        // Prints the matrices
        for (r = 0; r < 3; r++) {
            System.out.println();

            for (c = 0; c < 3; c++) {
                System.out.print("  " + matrix[r][c] + "  ");
            }
        }

        for (r = 0; r < 3; r++) {
            System.out.println();

            for (c = 0; c < 3; c++) {
                System.out.print("  " + rTemp[r][c] + "  ");
            }
        }

        for (r = 0; r < 3; r++) {
            System.out.println();

            for (c = 0; c < 3; c++) {
                System.out.print("  " + cTemp[r][c] + "  ");
            }
        }
    } 

    public static boolean ValidateMarkov(double[][] n) {
        double sum;

        for  (int c = 0; c < 3; c++) {
            sum = 0;
            for (int r = 0; r < 3; r++) {
                if (n[c][r] < 0) {
                    return false;
                }
                sum += n[c][r];
            }

           if (sum != 1) {
               return false;
            }
        }
        return true;
    }

    public static double[][] SortRows(double[][] m) {
        int r, c;
        double[][] rTemp = new double[3][3];

        for (r = 0; r < 2; r++)
            for (c = 0; c < 2 - c; c++)
                if (m[r][c] > m[r][c + 1]) {
                    rTemp[r][c] = m[r][c];
                    m[r][c] = m[r][c + 1];
                    m[r][c + 1] = rTemp[r][c + 1];
                }
        return rTemp;
    }

    public static double[][] SortColumns(double[][] n) {

        int r, c;
        double[][] cTemp = new double[3][3];

        for (c = 0; c < 2; c++)
            for (r = 0; r < 2 - r; r++)
                if (n[c][r] > n[c][r + 1]) {
                    cTemp[c][r] = n[c][r];
                    n[c][r] = n[c][r + 1];
                    n[c][r + 1] = cTemp[c][r + 1];
                }
        return cTemp;
    }
}

Answer 1

Please use camelCase for method names in Java, that helps to distinguish classes from methods. I believe the bug is you aren't storing the result of the calls here

SortRows(matrix); // <-- returns rTemp
SortColumns(matrix); // <-- returns cTemp

because you use (and return a new double[][] in both). You need something like

matrix = SortRows(matrix); // <-- sortRows(matrix);
matrix = SortColumns(matrix); // <-- sortColumns(matrix);