if your matrix  has large amounts of data that you are manupulating then it's
mush more efficient that you prefer native based api 's for this operation.

this code do the stuff.
any length matrix  in 2 dimension


public static int[][] multiplicate(int[][] a, int[][] b)
{
// Matrix a has m rows, and n cols
// Matrix b has n rows, and p cols
int m = a.length;
int n = ((int[])a[0]).length;
int p = ((int[])b[0]).length;
int[][] result = new int[m][p];

for (int i = 0; i < m; i++)
{
for (int j = 0; j < p; j++)
{
int partial = 0;
for (int h = 0; h < n; h++)
{
partial += a[i][h] * b[h][j];
}
res[i][j] = partial;
}
}

return result;
}