/** * 求一个3*3矩阵对角线元素之和 * */ public class Demo { public static void main(String[] args) { double sum = 0; int array[][] = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } }; for (int i = 0; i < 3; i++) for (int j = 0; j < 3; j++) { if (i == j) sum = sum + array[i][j]; } System.out.println(sum); } }