gregoriancalendar.java

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	    + 7 * (fields[WEEK_OF_YEAR]
		   + (fields[DAY_OF_WEEK] < getFirstDayOfWeek()? 0 : -1)
		   + (weekday < getFirstDayOfWeek()? -1 : 0))};
      }

    // As last resort return Jan, 1st.
    return new int[] {1, 0};
  }

  /**
   * Converts the time field values (<code>fields</code>) to
   * milliseconds since the epoch UTC (<code>time</code>). 
   */
  protected synchronized void computeTime()
  {
    int era = isSet[ERA] ? fields[ERA] : AD;
    int year = isSet[YEAR] ? fields[YEAR] : 1970;
    if (era == BC)
      year = 1 - year;

    int[] daysOfYear = getDayOfYear(year);

    int hour = 0;
    if (isSet[HOUR_OF_DAY])
      hour = fields[HOUR_OF_DAY];
    else if (isSet[HOUR])
      {
	hour = fields[HOUR];
        if (isSet[AM_PM] && fields[AM_PM] == PM)
	  hour += 12;
      }

    int minute = isSet[MINUTE] ? fields[MINUTE] : 0;
    int second = isSet[SECOND] ? fields[SECOND] : 0;
    int millis = isSet[MILLISECOND] ? fields[MILLISECOND] : 0;
    int millisInDay;

    if (isLenient())
      {
	// prevent overflow
	long allMillis = (((hour * 60L) + minute) * 60L + second) * 1000L
	  + millis;
	daysOfYear[1] += allMillis / (24 * 60 * 60 * 1000L);
	millisInDay = (int) (allMillis % (24 * 60 * 60 * 1000L));
      }
    else
      {
	if (hour < 0 || hour >= 24 || minute < 0 || minute > 59
	    || second < 0 || second > 59 || millis < 0 || millis >= 1000)
	  throw new IllegalArgumentException();
	millisInDay = (((hour * 60) + minute) * 60 + second) * 1000 + millis;
      }
    time = getLinearTime(year, daysOfYear[0], millisInDay);

    // Add the relative days after calculating the linear time, to
    // get right behaviour when jumping over the gregorianCutover.
    time += daysOfYear[1] * (24 * 60 * 60 * 1000L);


    TimeZone zone = getTimeZone();
    int rawOffset = isSet[ZONE_OFFSET]
      ? fields[ZONE_OFFSET] : zone.getRawOffset();

    int dayOfYear = daysOfYear[0] + daysOfYear[1];
    int month = (dayOfYear * 5 + 3) / (31 + 30 + 31 + 30 + 31);
    int day = (6 + (dayOfYear * 5 + 3) % (31 + 30 + 31 + 30 + 31)) / 5;
    int weekday = ((int) (time / (24 * 60 * 60 * 1000L)) + THURSDAY) % 7;
    if (weekday <= 0)
      weekday += 7;
    int dstOffset = isSet[DST_OFFSET]
      ? fields[DST_OFFSET] : (zone.getOffset((year < 0) ? BC : AD,
					     (year < 0) ? 1 - year : year,
					     month, day, weekday, millisInDay)
			      - zone.getRawOffset());
    time -= rawOffset + dstOffset;
    isTimeSet = true;
  }

  /**
   * Determines if the given year is a leap year.  
   *
   * The year should be positive and you can't give an ERA.  But
   * remember that before 4 BC there wasn't a consistent leap year
   * rule, so who cares.
   *
   * @param year a year use nonnegative value for BC.
   * @param gregorian if true, use gregorian leap year rule.
   * @return true, if the given year is a leap year, false otherwise.  */
  private boolean isLeapYear(int year, boolean gregorian)
  {
    if ((year & 3) != 0)
      // Only years divisible by 4 can be leap years
      return false;

    if (!gregorian)
      return true;

    // We rely on AD area here.
    return ((year % 100) != 0 || (year % 400) == 0);
  }

  /**
   * Get the linear day in days since the epoch, using the
   * Julian or Gregorian calendar as specified.  If you specify a
   * nonpositive year it is interpreted as BC as following: 0 is 1
   * BC, -1 is 2 BC and so on.  
   *
   * @param year the year of the date.
   * @param dayOfYear the day of year of the date; 1 based.
   * @param gregorian True, if we should use Gregorian rules.
   * @return the days since the epoch, may be negative.  */
  private int getLinearDay(int year, int dayOfYear, boolean gregorian)
  {
    // The 13 is the number of days, that were omitted in the Gregorian
    // Calender until the epoch.
    // We shift right by 2 instead of dividing by 4, to get correct
    // results for negative years (and this is even more efficient).
    int julianDay = ((year * (365 * 4 + 1)) >> 2) + dayOfYear -
      ((1970 * (365 * 4 + 1)) / 4 + 1 - 13);

    if (gregorian)
      {
	// subtract the days that are missing in gregorian calendar
	// with respect to julian calendar.
	//
	// Okay, here we rely on the fact that the gregorian
	// calendar was introduced in the AD era.  This doesn't work
	// with negative years.
	//
	// The additional leap year factor accounts for the fact that
	// a leap day is not seen on Jan 1 of the leap year.
	int gregOffset = (year / 400) - (year / 100) + 2;
	if (isLeapYear (year, true) && dayOfYear < 31 + 29)
	  --gregOffset;
	julianDay += gregOffset;
      }
    return julianDay;
  }

  /**
   * Converts the given linear day into era, year, month,
   * day_of_year, day_of_month, day_of_week, and writes the result
   * into the fields array.
   * @param day the linear day.  
   */
  private void calculateDay(int day, boolean gregorian)
  {
    // the epoch is a Thursday.
    int weekday = (day + THURSDAY) % 7;
    if (weekday <= 0)
      weekday += 7;
    fields[DAY_OF_WEEK] = weekday;

    // get a first approximation of the year.  This may be one 
    // year to big.
    int year = 1970 + (gregorian
		       ? ((day - 100) * 400) / (365 * 400 + 100 - 4 + 1)
		       : ((day - 100) * 4) / (365 * 4 + 1));
    if (day >= 0)
      year++;

    int firstDayOfYear = getLinearDay(year, 1, gregorian);

    // Now look in which year day really lies.
    if (day < firstDayOfYear)
      {
	year--;
	firstDayOfYear = getLinearDay(year, 1, gregorian);
      }

    day -= firstDayOfYear - 1;	// day of year,  one based.

    fields[DAY_OF_YEAR] = day;
    if (year <= 0)
      {
	fields[ERA] = BC;
	fields[YEAR] = 1 - year;
      }
    else
      {
	fields[ERA] = AD;
	fields[YEAR] = year;
      }

    int leapday = isLeapYear(year, gregorian) ? 1 : 0;
    if (day <= 31 + 28 + leapday)
      {
	fields[MONTH] = day / 32;	// 31->JANUARY, 32->FEBRUARY
	fields[DAY_OF_MONTH] = day - 31 * fields[MONTH];
      }
    else
      {
	// A few more magic formulas
	int scaledDay = (day - leapday) * 5 + 8;
	fields[MONTH] = scaledDay / (31 + 30 + 31 + 30 + 31);
	fields[DAY_OF_MONTH] = (scaledDay % (31 + 30 + 31 + 30 + 31)) / 5 + 1;
      }
  }

  /**
   * Converts the milliseconds since the epoch UTC
   * (<code>time</code>) to time fields
   * (<code>fields</code>). 
   */
  protected synchronized void computeFields()
  {
    boolean gregorian = (time >= gregorianCutover);

    TimeZone zone = getTimeZone();
    fields[ZONE_OFFSET] = zone.getRawOffset();
    long localTime = time + fields[ZONE_OFFSET];

    int day = (int) (localTime / (24 * 60 * 60 * 1000L));
    int millisInDay = (int) (localTime % (24 * 60 * 60 * 1000L));
    if (millisInDay < 0)
      {
	millisInDay += (24 * 60 * 60 * 1000);
	day--;
      }

    calculateDay(day, gregorian);
    fields[DST_OFFSET] =
      zone.getOffset(fields[ERA], fields[YEAR], fields[MONTH],
		     fields[DAY_OF_MONTH], fields[DAY_OF_WEEK],
		     millisInDay) - fields[ZONE_OFFSET];

    millisInDay += fields[DST_OFFSET];
    if (millisInDay >= 24 * 60 * 60 * 1000)
      {
	millisInDay -= 24 * 60 * 60 * 1000;
	calculateDay(++day, gregorian);
      }

    fields[DAY_OF_WEEK_IN_MONTH] = (fields[DAY_OF_MONTH] + 6) / 7;

    // which day of the week are we (0..6), relative to getFirstDayOfWeek
    int relativeWeekday = (7 + fields[DAY_OF_WEEK] - getFirstDayOfWeek()) % 7;

    fields[WEEK_OF_MONTH] = (fields[DAY_OF_MONTH] - relativeWeekday + 6) / 7;

    int weekOfYear = (fields[DAY_OF_YEAR] - relativeWeekday + 6) / 7;

    // Do the Correction: getMinimalDaysInFirstWeek() is always in the 
    // first week.
    int minDays = getMinimalDaysInFirstWeek();
    int firstWeekday =
      (7 + getWeekDay(fields[YEAR], minDays) - getFirstDayOfWeek()) % 7;
    if (minDays - firstWeekday < 1)
      weekOfYear++;
    fields[WEEK_OF_YEAR] = weekOfYear;


    int hourOfDay = millisInDay / (60 * 60 * 1000);
    fields[AM_PM] = (hourOfDay < 12) ? AM : PM;
    int hour = hourOfDay % 12;
    fields[HOUR] = (hour == 0) ? 12 : hour;
    fields[HOUR_OF_DAY] = hourOfDay;
    millisInDay %= (60 * 60 * 1000);
    fields[MINUTE] = millisInDay / (60 * 1000);
    millisInDay %= (60 * 1000);
    fields[SECOND] = millisInDay / (1000);
    fields[MILLISECOND] = millisInDay % 1000;


    areFieldsSet = isSet[ERA] = isSet[YEAR] = isSet[MONTH] =
      isSet[WEEK_OF_YEAR] = isSet[WEEK_OF_MONTH] =
      isSet[DAY_OF_MONTH] = isSet[DAY_OF_YEAR] = isSet[DAY_OF_WEEK] =
      isSet[DAY_OF_WEEK_IN_MONTH] = isSet[AM_PM] = isSet[HOUR] =
      isSet[HOUR_OF_DAY] = isSet[MINUTE] = isSet[SECOND] =
      isSet[MILLISECOND] = isSet[ZONE_OFFSET] = isSet[DST_OFFSET] = true;

  }

  /**
   * Compares the given calender with this.  
   * @param o the object to that we should compare.
   * @return true, if the given object is a calendar, that represents
   * the same time (but doesn't necessary have the same fields).
   * @XXX Should we check if time zones, locale, cutover etc. are equal?
   */
  public boolean equals(Object o)
  {
    if (!(o instanceof GregorianCalendar))
      return false;

    GregorianCalendar cal = (GregorianCalendar) o;
    return (cal.getTimeInMillis() == getTimeInMillis());
  }

//     /**
//      * Compares the given calender with this.  
//      * @param o the object to that we should compare.
//      * @return true, if the given object is a calendar, and this calendar
//      * represents a smaller time than the calender o.
//      */
//     public boolean before(Object o) {
//         if (!(o instanceof GregorianCalendar))
//             return false;

//         GregorianCalendar cal = (GregorianCalendar) o;
//         return (cal.getTimeInMillis() < getTimeInMillis());
//     }

//     /**
//      * Compares the given calender with this.  
//      * @param o the object to that we should compare.
//      * @return true, if the given object is a calendar, and this calendar
//      * represents a bigger time than the calender o.
//      */
//     public boolean after(Object o) {
//         if (!(o instanceof GregorianCalendar))
//             return false;

//         GregorianCalendar cal = (GregorianCalendar) o;
//         return (cal.getTimeInMillis() > getTimeInMillis());
//     }

  /**
   * Adds the specified amount of time to the given time field.  The
   * amount may be negative to subtract the time.  If the field overflows
   * it does what you expect: Jan, 25 + 10 Days is Feb, 4.
   * @param field the time field. One of the time field constants.
   * @param amount the amount of time.
   */
  public void add(int field, int amount)
  {
    switch (field)
      {
      case YEAR:
	complete();
	fields[YEAR] += amount;
	isTimeSet = false;
	break;
      case MONTH:
	complete();
	int months = fields[MONTH] + amount;
	fields[YEAR] += months / 12;
	fields[MONTH] = months % 12;
	if (fields[MONTH] < 0)
	  {
	    fields[MONTH] += 12;
	    fields[YEAR]--;
	  }
	isTimeSet = false;
	int maxDay = getActualMaximum(DAY_OF_MONTH);
	if (fields[DAY_OF_MONTH] > maxDay)
	  {
	    fields[DAY_OF_MONTH] = maxDay;
	    isTimeSet = false;
	  }
	break;
      case DAY_OF_MONTH:
      case DAY_OF_YEAR:
      case DAY_OF_WEEK:
	if (!isTimeSet)
	  computeTime();
	time += amount * (24 * 60 * 60 * 1000L);
	areFieldsSet = false;
	break;
      case WEEK_OF_YEAR:
      case WEEK_OF_MONTH:
      case DAY_OF_WEEK_IN_MONTH:
	if (!isTimeSet)