java.util.GregorianCalendar Maven / Gradle / Ivy

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This work corresponds to the API signatures of JSR 219: Foundation Profile 1.1. In the event of a discrepency between this work and the JSR 219 specification, which is available at http://www.jcp.org/en/jsr/detail?id=219, the latter takes precedence. */ package java.util; import java.io.IOException; import java.io.ObjectInputStream; /** * GregorianCalendar is a concrete subclass of * {@link Calendar} * and provides the standard calendar used by most of the world. * *

* The standard (Gregorian) calendar has 2 eras, BC and AD. * *

* This implementation handles a single discontinuity, which corresponds by * default to the date the Gregorian calendar was instituted (October 15, 1582 * in some countries, later in others). The cutover date may be changed by the * caller by calling setGregorianChange(). * *

* Historically, in those countries which adopted the Gregorian calendar first, * October 4, 1582 was thus followed by October 15, 1582. This calendar models * this correctly. Before the Gregorian cutover, GregorianCalendar * implements the Julian calendar. The only difference between the Gregorian * and the Julian calendar is the leap year rule. The Julian calendar specifies * leap years every four years, whereas the Gregorian calendar omits century * years which are not divisible by 400. * *

* GregorianCalendar implements proleptic Gregorian and * Julian calendars. That is, dates are computed by extrapolating the current * rules indefinitely far backward and forward in time. As a result, * GregorianCalendar may be used for all years to generate * meaningful and consistent results. However, dates obtained using * GregorianCalendar are historically accurate only from March 1, 4 * AD onward, when modern Julian calendar rules were adopted. Before this date, * leap year rules were applied irregularly, and before 45 BC the Julian * calendar did not even exist. * *

* Prior to the institution of the Gregorian calendar, New Year's Day was * March 25. To avoid confusion, this calendar always uses January 1. A manual * adjustment may be made if desired for dates that are prior to the Gregorian * changeover and which fall between January 1 and March 24. * *

Values calculated for the WEEK_OF_YEAR field range from 1 to * 53. Week 1 for a year is the earliest seven day period starting on * getFirstDayOfWeek() that contains at least * getMinimalDaysInFirstWeek() days from that year. It thus * depends on the values of getMinimalDaysInFirstWeek(), * getFirstDayOfWeek(), and the day of the week of January 1. * Weeks between week 1 of one year and week 1 of the following year are * numbered sequentially from 2 to 52 or 53 (as needed). * *

For example, January 1, 1998 was a Thursday. If * getFirstDayOfWeek() is MONDAY and * getMinimalDaysInFirstWeek() is 4 (these are the values * reflecting ISO 8601 and many national standards), then week 1 of 1998 starts * on December 29, 1997, and ends on January 4, 1998. If, however, * getFirstDayOfWeek() is SUNDAY, then week 1 of 1998 * starts on January 4, 1998, and ends on January 10, 1998; the first three days * of 1998 then are part of week 53 of 1997. * *

Values calculated for the WEEK_OF_MONTH field range from 0 * to 6. Week 1 of a month (the days with WEEK_OF_MONTH = * 1) is the earliest set of at least * getMinimalDaysInFirstWeek() contiguous days in that month, * ending on the day before getFirstDayOfWeek(). Unlike * week 1 of a year, week 1 of a month may be shorter than 7 days, need * not start on getFirstDayOfWeek(), and will not include days of * the previous month. Days of a month before week 1 have a * WEEK_OF_MONTH of 0. * *

For example, if getFirstDayOfWeek() is SUNDAY * and getMinimalDaysInFirstWeek() is 4, then the first week of * January 1998 is Sunday, January 4 through Saturday, January 10. These days * have a WEEK_OF_MONTH of 1. Thursday, January 1 through * Saturday, January 3 have a WEEK_OF_MONTH of 0. If * getMinimalDaysInFirstWeek() is changed to 3, then January 1 * through January 3 have a WEEK_OF_MONTH of 1. * *

* Example: *

*

 * // get the supported ids for GMT-08:00 (Pacific Standard Time)
 * String[] ids = TimeZone.getAvailableIDs(-8 * 60 * 60 * 1000);
 * // if no ids were returned, something is wrong. get out.
 * if (ids.length == 0)
 *     System.exit(0);
 *
 *  // begin output
 * System.out.println("Current Time");
 *
 * // create a Pacific Standard Time time zone
 * SimpleTimeZone pdt = new SimpleTimeZone(-8 * 60 * 60 * 1000, ids[0]);
 *
 * // set up rules for daylight savings time
 * pdt.setStartRule(Calendar.APRIL, 1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);
 * pdt.setEndRule(Calendar.OCTOBER, -1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);
 *
 * // create a GregorianCalendar with the Pacific Daylight time zone
 * // and the current date and time
 * Calendar calendar = new GregorianCalendar(pdt);
 * Date trialTime = new Date();
 * calendar.setTime(trialTime);
 *
 * // print out a bunch of interesting things
 * System.out.println("ERA: " + calendar.get(Calendar.ERA));
 * System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
 * System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
 * System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
 * System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
 * System.out.println("DATE: " + calendar.get(Calendar.DATE));
 * System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
 * System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
 * System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
 * System.out.println("DAY_OF_WEEK_IN_MONTH: "
 *                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));
 * System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));
 * System.out.println("HOUR: " + calendar.get(Calendar.HOUR));
 * System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));
 * System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));
 * System.out.println("SECOND: " + calendar.get(Calendar.SECOND));
 * System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));
 * System.out.println("ZONE_OFFSET: "
 *                    + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000)));
 * System.out.println("DST_OFFSET: "
 *                    + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000)));
 *
 * System.out.println("Current Time, with hour reset to 3");
 * calendar.clear(Calendar.HOUR_OF_DAY); // so doesn't override
 * calendar.set(Calendar.HOUR, 3);
 * System.out.println("ERA: " + calendar.get(Calendar.ERA));
 * System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
 * System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
 * System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
 * System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
 * System.out.println("DATE: " + calendar.get(Calendar.DATE));
 * System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
 * System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
 * System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
 * System.out.println("DAY_OF_WEEK_IN_MONTH: "
 *                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));
 * System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));
 * System.out.println("HOUR: " + calendar.get(Calendar.HOUR));
 * System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));
 * System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));
 * System.out.println("SECOND: " + calendar.get(Calendar.SECOND));
 * System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));
 * System.out.println("ZONE_OFFSET: "
 *        + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000))); // in hours
 * System.out.println("DST_OFFSET: "
 *        + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000))); // in hours
 * 

*

* To obtain a pure Julian calendar, set the change date to * Date(Long.MAX_VALUE). To obtain a pure Gregorian calendar, * set the change date to Date(Long.MIN_VALUE). * * @param date the given Gregorian cutover date. */ public void setGregorianChange(Date date) { } /** * Gets the Gregorian Calendar change date. This is the point when the * switch from Julian dates to Gregorian dates occurred. Default is * October 15, 1582. Previous to this, dates will be in the Julian * calendar. * @return the Gregorian cutover date for this calendar. */ public final Date getGregorianChange() { return null; } /** * Determines if the given year is a leap year. Returns true if the * given year is a leap year. * @param year the given year. * @return true if the given year is a leap year; false otherwise. */ public boolean isLeapYear(int year) { return false; } /** * Compares this GregorianCalendar to an object reference. * @param obj the object reference with which to compare * @return true if this object is equal to obj; false otherwise */ public boolean equals(Object obj) { return false; } /** * Override hashCode. * Generates the hash code for the GregorianCalendar object */ public int hashCode() { return 0; } /** * Adds the specified (signed) amount of time to the given time field, * based on the calendar's rules. *

Add rule 1. The value of field * after the call minus the value of field before the * call is amount, modulo any overflow that has occurred in * field. Overflow occurs when a field value exceeds its * range and, as a result, the next larger field is incremented or * decremented and the field value is adjusted back into its range.

Add rule 2. If a smaller field is expected to be * invariant, but it is impossible for it to be equal to its * prior value because of changes in its minimum or maximum after * field is changed, then its value is adjusted to be as close * as possible to its expected value. A smaller field represents a * smaller unit of time. HOUR is a smaller field than * DAY_OF_MONTH. No adjustment is made to smaller fields * that are not expected to be invariant. The calendar system * determines what fields are expected to be invariant.

* Example: Consider a GregorianCalendar * originally set to December 31, 1999. Calling roll(Calendar.MONTH, true) * sets the calendar to January 31, 1999. The Year field is unchanged * because it is a larger field than MONTH.

* Example: Consider a GregorianCalendar * originally set to August 31, 1999. Calling roll(Calendar.MONTH, * 8) sets the calendar to April 30, 1999. Using a * GregorianCalendar, the DAY_OF_MONTH field cannot * be 31 in the month April. DAY_OF_MONTH is set to the closest possible * value, 30. The YEAR field maintains the value of 1999 because it * is a larger field than MONTH. *

* Example: Consider a GregorianCalendar * originally set to Sunday June 6, 1999. Calling * roll(Calendar.WEEK_OF_MONTH, -1) sets the calendar to * Tuesday June 1, 1999, whereas calling * add(Calendar.WEEK_OF_MONTH, -1) sets the calendar to * Sunday May 30, 1999. This is because the roll rule imposes an * additional constraint: The MONTH must not change when the * WEEK_OF_MONTH is rolled. Taken together with add rule 1, * the resultant date must be between Tuesday June 1 and Saturday June * 5. According to add rule 2, the DAY_OF_WEEK, an invariant * when changing the WEEK_OF_MONTH, is set to Tuesday, the * closest possible value to Sunday (where Sunday is the first day of the * week).