private static void checkGrade(int grade) {
        if (grade >= 90) {
            System.out.println("优秀");
        } else if (grade >= 80) {
            System.out.println("良好");
        } else if (grade >= 70) {
            System.out.println("中等");
        } else if (grade >= 60) {
            System.out.println("及格");
        } else {
            System.out.println("不及格");
        }
    }

private static void testWhile() {
    int i = 1;
    int sum = 0;
    while (i <= 10) {
        sum += i;
        i++;
    }
    do {
        sum += i;
        i++;
    } while (i <= 10);
    System.out.println("sum:" + sum);
}

private static void testFor() {
    for (int i = 1; i < 20; i++) {
        if (i % 2 == 0) {
            System.out.println(i + "是偶数");
            continue;
        }
        System.out.println(i + "是奇数");
    }
}

private static void testSwitch() {
    int sex = 0;
    switch (sex) {
        case 0:
            System.out.println("男性");
            break;
        case 1:
            System.out.println("男性");
            break;
        default:
            System.out.println("未知");
            break;
    }
}