Question

我希望这不是JDK的错误，或者我很想兑现我所有的银行帐户并将其放入床垫中... 这是代码。请注意，将日期设置为12月29日会立即将年份推迟到2020年。此外，toString（）输出还显示Calendar似乎认为星期数是“ 1”。

import java.util.*; // headers MUST be above the first class
import java.text.*;

public class JDKCalendarBug {

    public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("MM-dd-YYYY kk:mm");
        Calendar cal = java.util.Calendar.getInstance(TimeZone
                .getTimeZone("EST"));
        cal.clear();
        cal.set(Calendar.YEAR, 2019);
        cal.set(Calendar.MONTH, Calendar.DECEMBER);

        cal.set(Calendar.DAY_OF_MONTH, 26);
        Date t = cal.getTime();
        System.out.print("\n"+sdf.format(t));
        System.out.print("\n"+cal.toString());

        cal.set(Calendar.DAY_OF_MONTH, 27);
        t = cal.getTime();
        System.out.print("\n"+sdf.format(t));
        System.out.print("\n"+cal.toString());

        cal.set(Calendar.DAY_OF_MONTH, 28);
        t = cal.getTime();
        System.out.print("\n"+sdf.format(t));
        System.out.print("\n"+cal.toString());

        cal.set(Calendar.DAY_OF_MONTH, 29);
        t = cal.getTime();
        System.out.print("\n"+sdf.format(t));
        System.out.print("\n"+cal.toString());

    }

}

输出：

12-26-2019 24:00   java.util.GregorianCalendar [time = 1577336400000，areFieldsSet = true，areAllFieldsSet = false，lenient = true，zone = sun.util.calendar.ZoneInfo [id =“ EST”，offset = -18000000，dstSavings = 0，useDaylight = false ，transitions = 0，lastRule = null]，firstDayOfWeek = 1，minimalDaysInFirstWeek = 1，ERA = ?, YEAR = 2019，MONTH = 11，WEEK_OF_YEAR = ?, WEEK_OF_MONTH = ?, DAY_OF_MONTH = 26，DAY_OF_YEAR = ?, DAY_OF_WEEK = ?, DAY_OF_WEEK_IN_MONTH = ?, AM_PM = ?, HOUR = ?, HOUR_OF_DAY = ?, MINUTE = ?, SECOND = ?, MILLISECOND = ?, ZONE_OFFSET = ?, DST_OFFSET =？]

12-27-2019 24:00   java.util.GregorianCalendar [time = 1577422800000，areFieldsSet = true，areAllFieldsSet = false，lenient = true，zone = sun.util.calendar.ZoneInfo [id =“ EST”，offset = -18000000，dstSavings = 0，useDaylight = false ，transitions = 0，lastRule = null]，firstDayOfWeek = 1，minimalDaysInFirstWeek = 1，ERA = 1，YEAR = 2019，MONTH = 11，WEEK_OF_YEAR = 52，WEEK_OF_MONTH = 4，DAY_OF_MONTH = 27，DAY_OF_YEAR = 361，DAY_OF_WEEK = 6， DAY_OF_WEEK_IN_MONTH = 4，AM_PM = 0，HOUR = 0，HOUR_OF_DAY = 0，MINUTE = 0，SECOND = 0，MILLISECOND = 0，ZONE_OFFSET = -18000000，DST_OFFSET = 0] 12-28-2019 24:00   java.util.GregorianCalendar [time = 1577509200000，areFieldsSet = true，areAllFieldsSet = false，lenient = true，zone = sun.util.calendar.ZoneInfo [id =“ EST”，offset = -18000000，dstSavings = 0，useDaylight = false ，transitions = 0，lastRule = null]，firstDayOfWeek = 1，minimumDaysInFirstWeek = 1，ERA = 1，YEAR = 2019，MONTH = 11，WEEK_OF_YEAR = 52，WEEK_OF_MONTH = 4，DAY_OF_MONTH = 28，DAY_OF_YEAR = 362，DAY_OF_WEEK = 7， DAY_OF_WEEK_IN_MONTH = 4，AM_PM = 0，HOUR = 0，HOUR_OF_DAY = 0，MINUTE = 0，SECOND = 0，MILLISECOND = 0，ZONE_OFFSET = -18000000，DST_OFFSET = 0]

12-29-2020 24:00   java.util.GregorianCalendar [time = 1577595600000，areFieldsSet = true，areAllFieldsSet = false，lenient = true，zone = sun.util.calendar.ZoneInfo [id =“ EST”，offset = -18000000，dstSavings = 0，useDaylight = false ，transitions = 0，lastRule = null]，firstDayOfWeek = 1，minimalDaysInFirstWeek = 1，ERA = 1，YEAR = 2019，MONTH = 11，WEEK_OF_YEAR = 1，WEEK_OF_MONTH = 5，DAY_OF_MONTH = 29，DAY_OF_YEAR = 363，DAY_OF_WEEK = 1， DAY_OF_WEEK_IN_MONTH = 5，AM_PM = 0，HOUR = 0，HOUR_OF_DAY = 0，MINUTE = 0，SECOND = 0，MILLISECOND = 0，ZONE_OFFSET = -18000000，DST_OFFSET = 0]

Answer 1

问题出在SimpleDateFormat上。如果将格式字符串更改为小写y，则日期格式正确为12-29-2019 24:00

new SimpleDateFormat("MM-dd-yyyy kk:mm")

Y对应于“周年”，与“年”不同，并非所有日历都支持。根据{{3}}：

如果指定周年“ Y”且日历不支持周年，则改用日历年（'y'）。的支持可以通过致电来测试周年 getCalendar（）。isWeekDateSupported（）。

在这种情况下，由于基本的Calendar实现是GregorianCalendar，因此支持“星期”。根据其JavaDocs：

一周的一年与WEEK_OF_YEAR周期保持同步。之间的所有星期前一周和后一周（含）具有相同的周年值。因此，一周的第一天和最后一天可能会有所不同日历年的值。

无法创建代表2019年12月29日的Date对象

1 个答案: