Here is my solution in java:

int max = -64, temp;
    for (int i = 0; i < 4; i++) {
        for (int j = 0; j < 4; j++) {
            temp = arr[i][j] + arr[i][j+1] + arr[i][j+2] +
                                arr[i+1][j+1] +
                    arr[i+2][j] + arr[i+2][j+1] + arr[i+2][j+2];
            if (temp > max){
                max = temp;
            }
        }
    }
    System.out.println(max);