求一个 3*3 矩阵对角线元素之和

package cskaoyan;
 
public class cskaoyan29 {
    @org.junit.Test
    public void diagonal() {
        java.util.Scanner in = new java.util.Scanner(System.in);
        int[][] arr = new int[3][3];
 
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                arr[i][j] = in.nextInt();
            }
        }
 
        sum(arr);
        in.close();
    }
 
    private void sum(int[][] arr) {
        int sum1 = 0;
        int sum2 = 0;
 
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                if (i == j) {
                    sum1 += arr[i][j];
                }
 
                if (j == arr[i].length - i - 1) {
                    sum2 += arr[i][j];
                }
            }
        }
 
        System.out.println("主对角线元素之和:" + sum1);
        System.out.println("副对角线元素之和:" + sum2);
    }
}