How to multiply two dimensional array by factor

Question

I have two dimensional array

private static int [][] n = {{1, 2, 3, 4}, {5, 6, 7, 8}}; 

And I have

int m = 3; 

How can I multiply each element in my two dimensional array by 3?
So that the output would be like this:

{{3, 6, 9, 12},{15, 18, 21, 24}}

Also, if I had a matrix like

{{1, 2, 3, 4, 5}, 
{6, 7, 8, 9, 10}, 
{11, 12, 13, 14, 15}, 
{16, 17, 18, 19, 20}, 
{21, 22, 23, 24, 25}}, 

How would I print the diagonal elements?

{1,7,13,19,25} and {5,9,12,17,20}

I'd like to know algorithm, because for multiplying dimensional array I used

private static int[] n = {1, 2, 3, 4, 5, 6, 7};

private static int[] multiply(int[] n, int m) {

    int array[] = new int[n.length];
    for (int i = 0; i < n.length; i++) {
        array[i] = n[i] * m;
    }
    return array;

}

Answer 1

Just iterate both dimensions:

private static int[][] multiply(int[][] n, int m) {
    int array[][] = new int[n.length][];
    for (int i = 0; i < n.length; i++) {
        array[i] = new int[n[i].length];
        for (int j = 0; j < n[i].length; j++) {
            array[i][j] = n[i][j] * m;
        }
    }
    return array;
}