Package java.util

Class GregorianCalendar

java.lang.Object
java.util.Calendar
java.util.GregorianCalendar
All Implemented Interfaces:
Serializable, Cloneable, Comparable<Calendar>
public class GregorianCalendar
extends Calendar
GregorianCalendar is a concrete subclass of 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 or 1 to 4 or 5. 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
See Also:
Calendar, TimeZone, Serialized Form

  • Field Details

  • Constructor Details

    • GregorianCalendar

      public GregorianCalendar()
      Constructs a new GregorianCalendar initialized to the current date and time with the default Locale and TimeZone.

    • GregorianCalendar

      public GregorianCalendar​(int year, int month, int day)
      Constructs a new GregorianCalendar initialized to midnight in the default TimeZone and Locale on the specified date.
      Parameters:
      year - the year.
      month - the month.
      day - the day of the month.

    • GregorianCalendar

      public GregorianCalendar​(int year, int month, int day, int hour, int minute)
      Constructs a new GregorianCalendar initialized to the specified date and time in the default TimeZone and Locale.
      Parameters:
      year - the year.
      month - the month.
      day - the day of the month.
      hour - the hour.
      minute - the minute.

    • GregorianCalendar

      public GregorianCalendar​(int year, int month, int day, int hour, int minute, int second)
      Constructs a new GregorianCalendar initialized to the specified date and time in the default TimeZone and Locale.
      Parameters:
      year - the year.
      month - the month.
      day - the day of the month.
      hour - the hour.
      minute - the minute.
      second - the second.

    • GregorianCalendar

      public GregorianCalendar​(Locale locale)
      Constructs a new GregorianCalendar initialized to the current date and time and using the specified Locale and the default TimeZone.
      Parameters:
      locale - the Locale.

    • GregorianCalendar

      public GregorianCalendar​(TimeZone timezone)
      Constructs a new GregorianCalendar initialized to the current date and time and using the specified TimeZone and the default Locale.
      Parameters:
      timezone - the TimeZone.

    • GregorianCalendar

      public GregorianCalendar​(TimeZone timezone, Locale locale)
      Constructs a new GregorianCalendar initialized to the current date and time and using the specified TimeZone and Locale.
      Parameters:
      timezone - the TimeZone.
      locale - the Locale.

  • Method Details

    • add

      public void add​(int field, int value)
      Adds the specified amount to a Calendar field.
      Specified by:
      add in class Calendar
      Parameters:
      field - the Calendar field to modify.
      value - the amount to add to the field.
      Throws:
      IllegalArgumentException - if the specified field is DST_OFFSET or ZONE_OFFSET.

    • computeFields

      protected void computeFields()
      Description copied from class: Calendar
      Computes the Calendar fields from time.
      Specified by:
      computeFields in class Calendar

    • computeTime

      protected void computeTime()
      Description copied from class: Calendar
      Computes time from the Calendar fields.
      Specified by:
      computeTime in class Calendar

    • equals

      public boolean equals​(Object object)
      Returns true if object is a GregorianCalendar with the same properties.
      Overrides:
      equals in class Calendar
      Parameters:
      object - the object to compare this instance with.
      Returns:
      true if the given object is equal to this Calendar, false otherwise.
      See Also:
      Object.hashCode()

    • getActualMaximum

      public int getActualMaximum​(int field)
      Description copied from class: Calendar
      Returns the maximum value of the given field for the current date. For example, the maximum number of days in the current month.
      Overrides:
      getActualMaximum in class Calendar

    • getActualMinimum

      public int getActualMinimum​(int field)
      Gets the minimum value of the specified field for the current date. For the gregorian calendar, this value is the same as getMinimum().
      Overrides:
      getActualMinimum in class Calendar
      Parameters:
      field - the field.
      Returns:
      the minimum value of the specified field.

    • getGreatestMinimum

      public int getGreatestMinimum​(int field)
      Gets the greatest minimum value of the specified field. For the gregorian calendar, this value is the same as getMinimum().
      Specified by:
      getGreatestMinimum in class Calendar
      Parameters:
      field - the field.
      Returns:
      the greatest minimum value of the specified field.

    • getGregorianChange

      public final Date getGregorianChange()
      Returns the gregorian change date of this calendar. This is the date on which the gregorian calendar came into effect.
      Returns:
      a Date which represents the gregorian change date.

    • getLeastMaximum

      public int getLeastMaximum​(int field)
      Gets the smallest maximum value of the specified field. For example, 28 for the day of month field.
      Specified by:
      getLeastMaximum in class Calendar
      Parameters:
      field - the field.
      Returns:
      the smallest maximum value of the specified field.

    • getMaximum

      public int getMaximum​(int field)
      Gets the greatest maximum value of the specified field. For example, 31 for the day of month field.
      Specified by:
      getMaximum in class Calendar
      Parameters:
      field - the field.
      Returns:
      the greatest maximum value of the specified field.

    • getMinimum

      public int getMinimum​(int field)
      Gets the smallest minimum value of the specified field.
      Specified by:
      getMinimum in class Calendar
      Parameters:
      field - the field.
      Returns:
      the smallest minimum value of the specified field.

    • hashCode

      public int hashCode()
      Description copied from class: Object
      Returns an integer hash code for this object. By contract, any two objects for which Object.equals(java.lang.Object) returns true must return the same hash code value. This means that subclasses of Object usually override both methods or neither method.

      Note that hash values must not change over time unless information used in equals comparisons also changes.

      See Writing a correct hashCode method if you intend implementing your own hashCode method.

      Overrides:
      hashCode in class Calendar
      Returns:
      this object's hash code.
      See Also:
      Object.equals(java.lang.Object)

    • isLeapYear

      public boolean isLeapYear​(int year)
      Returns true if year is a leap year.

    • roll

      public void roll​(int field, int value)
      Adds the specified amount the specified field and wraps the value of the field when it goes beyond the maximum or minimum value for the current date. Other fields will be adjusted as required to maintain a consistent date.
      Overrides:
      roll in class Calendar
      Parameters:
      field - the field to roll.
      value - the amount to add.
      Throws:
      IllegalArgumentException - if an invalid field is specified.

    • roll

      public void roll​(int field, boolean increment)
      Increments or decrements the specified field and wraps the value of the field when it goes beyond the maximum or minimum value for the current date. Other fields will be adjusted as required to maintain a consistent date. For example, March 31 will roll to April 30 when rolling the month field.
      Specified by:
      roll in class Calendar
      Parameters:
      field - the field to roll.
      increment - true to increment the field, false to decrement.
      Throws:
      IllegalArgumentException - if an invalid field is specified.

    • setGregorianChange

      public void setGregorianChange​(Date date)
      Sets the gregorian change date of this calendar.