Iterate through a matrix with openJML

I have a class with a matrix initialized with all 0 and 1 in a specific position:

public class MatrixTest {
    /*@ spec_public @*/ int[][] griglia;

    //@requires true;
    //@ensures griglia[2][3] == 1;
    public MatrixTest() {
        griglia = new int[6][6];

        for (int i=0; i < 6; i++) {
            for (int j=0; j < 6; j++){
                griglia[i][j] = 0;
            }
        }

        griglia[2][3] = 1;

    }
}

I would like to add an invariant to check that i always have only one 1 cell with a value of 1 and 35 cells with a value of 0. I tried doing that:

//@ public invariant (\num_of int i, j; i >= 0 && i < 6 && j >= 0 && j < 6; griglia[i][j] == 1) == 1;

But it gives me invariant error just after the constructor. How can i iterate through a matrix to check a property?

After a lot of research, it seems like you can only do it with \forall, other commands didn't work for me.

\forall int i; i >= 0 && i < matrix.length; (\forall int j; j >= 0 && j < matrix[i].length; /* your check here */)

So, just don't use openJML if you are working with multi-dimensional arrays