1572. Matrix Diagonal Sum java

https://leetcode.com/problems/matrix-diagonal-sum/?envType=study-plan&id=programming-skills-i 

class Solution {
    public int diagonalSum(int[][] mat){
        int sum = 0;
        for(int i = 0; i < mat.length; i++){
            for(int j = 0; j < mat.length; j++){
                if (i==j || i+j == mat.length - 1){
                    sum += mat[i][j];
                }
            }        }
        return sum;
    }

    public static void main(String[] args){
        Solution sol = new Solution();
        int[][] mat = {{1,1,1,1},
        {1,1,1,1},
        {1,1,1,1},
        {1,1,1,1}};
        System.out.println(sol.diagonalSum(mat));
    }
}