...

        int maxSum = Integer.MIN_VALUE;
        
        for (int i = 0; i <= arr.size() - 3; i++) {
            for (int j = 0; j <= arr.size() - 3; j++) {
                int currentSum = calcSum(i, j, arr);
                if (currentSum > maxSum) {
                    maxSum = currentSum;
                }
            }
        }
				...

    private static int calcSum(int vEdge, int hEdge, List<List<Integer>> arr) {
        int[][] hourGlassCooridnates = {{0, 0}, {0, 1}, {0, 2}, {1, 1}, {2, 0}, {2, 1}, {2, 2}};   
        int sum = 0;
        for (int[] coordinate : hourGlassCooridnates) {
            int i = coordinate[0];
            int j = coordinate[1];
            sum += arr.get(vEdge + i).get(hEdge + j);
        }
        return sum;
    }