求一个3*3矩阵对角线元素之和

	public static void main(String[] args) {
		int[][] a = new int[][] { { 100, 2, 5 }, { 4, 7, 6 }, { 17, 8, 9 } };
		matrSum(a);
	}
       /*100   2     5
     0   (0)   (1)  (2)
         4     7     6
     1   (0)   (1)  (2)
        17    8      9
     2  (0)   (1)  (2)
        */
	private static void matrSum(int[][] a) {
		int sum1 = 0;
		int sum2 = 0;
		for (int i = 0; i < a.length; i++)
			for (int j = 0; j < a[i].length; j++) {
				if (i == j) {
					sum1 += a[i][j];
				}
				if (j == a.length - i - 1) {
					sum2 += a[i][j];
				}
			}
		System.out.println("矩阵对角线之和分别是：" + sum1 + "和" + sum2);
	}