计算一周内的日期。通过窗口输入今天日期，获取今天是周几。

GergorianCalendar类

public static void dateToWeek3() {
    Scanner cin = new Scanner(System.in);
    System.out.println("请输入年，月，日：");
    while (cin.hasNext()) {
        int year = cin.nextInt();
        int month = cin.nextInt();
        int day = cin.nextInt();
        GregorianCalendar gre = new GregorianCalendar();
        //年要减去1900，月份是0-11
        Date date = new Date(year - 1900, month - 1, day);
        gre.setTime(date);
        //0是星期天
        int weekday = gre.get(Calendar.DAY_OF_WEEK) - 1;
        String[] s = {"星期天", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六",};
        System.out.println(year + " " + month + " " + day + " " + s[weekday]);
    }
}