打印二维数组

for

for (int[] arr : ns) {
    for (int n : arr) {
        System.out.print(n);
        System.out.print(', ');
    }
    System.out.println();
}

Arrays.deepToString()

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[][] ns = {
            { 1, 2, 3, 4 },
            { 5, 6, 7, 8 },
            { 9, 10, 11, 12 }
        };
        System.out.println(Arrays.deepToString(ns));
    }
}

计算数组平均值

public class Main {
    public static void main(String[] args) {
        // 用二维数组表示的学生成绩:
        int[][] scores = { 
                { 82, 90, 91 }, 
                { 68, 72, 64 }, 
                { 95, 91, 89 }, 
                { 67, 52, 60 }, 
                { 79, 81, 85 }, 
        };
        double sum=0;
        for(int i=0;i<scores.length;i++)
        {
            for(int j=0;j<scores[i].length;j++)
            {
                sum+=scores[i][j];
            }
        }
        double average = sum/(scores.length*scores[1].length);
        System.out.println(average);
        if (Math.abs(average - 77.733333) < 0.000001) {
            System.out.println("测试成功");
        } else {
            System.out.println("测试失败");
        }
    }
}