3×3矩阵对角线元素之和 Java

编写一个程序，求一个3×3矩阵对角线元素之和。利用双重for循环控制输入二维数组，再将a[i][i]累加后输出

package cn.myAlgorithm;

import java.util.Scanner;

//求一个3*3矩阵对角线元素之和 
class SumOfMatrixDiagonal {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int[][] arr = new int[3][3];
        for (int i = 1; i <= arr.length; i++) {
            for (int j = 1; j <= arr.length; j++) {
                System.out.printf("请输入矩阵第%d行第%d个元素：\n", i, j);
                arr[i - 1][j - 1] = scanner.nextInt();
            }
        }

        int sum = 0;
        for (int i = 1; i <= arr.length; i++) {
            for (int j = 1; j <= arr.length; j++) {
                if (i == j) {
                    sum += arr[i - 1][j - 1];
                }
            }
        }
        System.out.println("矩阵对角线和为：" + sum);
    }
}