矩阵对角线和

题目：求一个3*3矩阵对角线元素之和(升级版:可以打印任何一个n*n矩阵的对角线的和)

public class Arithmetic_matrixSum {
    public static void main(String[] args) {
        int[][] arr = new int[3][3];
        setMatrix(arr);
        printMatrix(arr);
        getMatrixDiagonalSum(arr);
    }
    /**设置随机矩阵*/
    public static void setMatrix(int[][] arr){
        Random random = new Random();
        int num = 0;
        for (int i = 0; i < arr.length; i++) {    //行
            for (int j = 0; j < arr[i].length; j++) {   //列
                num = random.nextInt(100);
                arr[i][j] = num;
            }
        }
    }
    /**打印矩阵*/
    public static void printMatrix(int[][] arr){
        for (int i = 0; i < arr.length; i++) {    //行
            for (int j = 0; j < arr[i].length; j++) {    //列
                System.out.print(arr[i][j]+"\t");
            }
            System.out.println("");
        }
    }
    /**求矩阵对角线和*/
    public static void getMatrixDiagonalSum(int[][] arr){
        int sum = 0;
        if (arr==null||(arr.length!=arr[0].length)) {    //不是正方形矩阵
            System.out.println("该矩阵无对角线,请输入n*n矩阵");
            return;
        }
        System.out.println("求对角线:");
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) { 
                if (i==j) {    //当行等于列时
                    sum += arr[i][j];
                    System.out.print(arr[i][j]+"\t");
                }
            }
        }
        System.out.println("一条对角线和"+sum);
        sum = 0;
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) { 
                if (i+j==arr.length-1) {    //另一条对角线规律
                    sum += arr[i][j];
                    System.out.print(arr[i][j]+"\t");
                }
            }
        }
        System.out.println("另一条对角线和"+sum);
    }
}

源码