Java日历-一周的第一天VS实际最小值

LoganMzz 发表于 Dev

洛根·马兹

我正在测试我们的日期管理框架的一部分，该框架应该重置一些Calendar字段（使用实际的minimum）。

然而，当改变周的第一天，日历总是返回SUNDAY（1）的实际最小为周的一天。是虫子吗？

import java.util.*;

public class Main {
  public static void main(String[] args) {
    System.out.printf("Java specification: %s%n", System.getProperty("java.vm.specification.version"));
    System.out.printf("Java version: %s%n", System.getProperty("java.specification.version"));
    System.out.printf("VM version: %s%n", System.getProperty("java.vm.version"));

    Calendar cal = Calendar.getInstance(TimeZone.getTimeZone("UTC"));

    int[] days = { 1, 5, 7 };
    for (int day : days) {
      cal.setTimeInMillis(0L);
      cal.setFirstDayOfWeek(day);
      System.out.printf("expected: %d, actual: %d%n", day, cal.getActualMinimum(Calendar.DAY_OF_WEEK));
    }
  }
}

凯瓦尔

您应该使用cal.getFirstDayOfWeek（）来代替cal.getActualMinimum（Calendar.DAY_OF_WEEK）

因为cal.getActualMinimum（Calendar.DAY_OF_WEEK）将始终返回星期日，请查看java源代码中getActualMinimum（Calendar.DAY_OF_WEEK）的实现

  public int getActualMinimum(int field) {
        if (field == DAY_OF_MONTH) {
            GregorianCalendar gc = getNormalizedCalendar();
            int year = gc.cdate.getNormalizedYear();
            if (year == gregorianCutoverYear || year == gregorianCutoverYearJulian) {
                long month1 = getFixedDateMonth1(gc.cdate, gc.calsys.getFixedDate(gc.cdate));
                BaseCalendar.Date d = getCalendarDate(month1);
                return d.getDayOfMonth();
            }
        }
        return getMinimum(field);
    }

而getMinimum是：-

   public int getMinimum(int field) {
        return MIN_VALUES[field];
    }

MIN_VALUES数组定义为：-

 static final int MIN_VALUES[] = {
        BCE,            // ERA
        1,              // YEAR
        JANUARY,        // MONTH
        1,              // WEEK_OF_YEAR
        0,              // WEEK_OF_MONTH
        1,              // DAY_OF_MONTH
        1,              // DAY_OF_YEAR
        SUNDAY,         // DAY_OF_WEEK
        1,              // DAY_OF_WEEK_IN_MONTH
        AM,             // AM_PM
        0,              // HOUR
        0,              // HOUR_OF_DAY
        0,              // MINUTE
        0,              // SECOND
        0,              // MILLISECOND
        -13*ONE_HOUR,   // ZONE_OFFSET (UNIX compatibility)
        0               // DST_OFFSET
    };