private static void avgScores(){
    // 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 },
    };
    // TODO:    double average = 0;
    System.out.println(average);
    int sum = 0;
    int length = 0;
    for (int[] ns : scores) {
        length += ns.length;
        for (int n : ns) {
            sum += n;
        }
    }
    average = sum / length;
    System.out.println("所有同学成绩平均值" + average);
    if (Math.abs(average - 77.733333) < 0.000001) { 
        System.out.println("测试成功");
    } else {
        System.out.println("测试失败");
    }
}