Java matrix multiplication 3x2 and 2x3, how to fix ArrayIndexOutOfBoundsException

Question

This method works for multiplication of 2x2 and 2x2 matrices only, but it's not working for 3x2 and 2x3. It results in

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 2 out of bounds for length 2

What am I doing wrong?

public class MultiplyMatrix {
    public static int[][] multiply(int[][] a, int[][] b) {

        int r1 = a[0].length, c1 = a.length; //2 3
        int r2 = b[0].length, c2 = b.length; //3 2

        int[][] multiply = new int[r1][c2];

        for (int i = 0; i < r1; i++) {
            for (int j = 0; j < c2; j++) {
                for (int k = 0; k < c1; k++) {
                    multiply[i][j] += a[i][k] * b[k][j];
                }
            }
        }
        return multiply;
    }

    public static void main(String[] args) {

        System.out.println("Test your code here!\n");

        // Get a result of your code

        int[][] a = { {1, 2, 3}, {4, 5, 6} };
        int[][] b = { {7, 8}, {9, 10}, {11, 12} };


        int[][] result = multiply(a, b);
        System.out.println(Arrays.deepToString(result).replace("],", "]\n"));
    }
}

because unlike wht you expect r1 is 3 and c1 is 2. you mistook the ordering — experiment unit 1998X, Feb 28 '23 at 04:03
when you pass 2x3, inside your code it is applying a for loop for a 3x2 — experiment unit 1998X, Feb 28 '23 at 04:08

score 0 · Answer 1 · answered Feb 28 '23 at 08:23

0

I think, you should edit the code like this

...
        int r1 = a.length, c1 = a[0].length; //2 3
        int r2 = b.length, c2 = b[0].length; //3 2
...

answered Feb 28 '23 at 08:23

fixcer

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Java matrix multiplication 3x2 and 2x3, how to fix ArrayIndexOutOfBoundsException

1 Answers1