gregoriancalendar.java

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	  computeTime();
	time += amount * (7 * 24 * 60 * 60 * 1000L);
	areFieldsSet = false;
	break;
      case AM_PM:
	if (!isTimeSet)
	  computeTime();
	time += amount * (12 * 60 * 60 * 1000L);
	areFieldsSet = false;
	break;
      case HOUR:
      case HOUR_OF_DAY:
	if (!isTimeSet)
	  computeTime();
	time += amount * (60 * 60 * 1000L);
	areFieldsSet = false;
	break;
      case MINUTE:
	if (!isTimeSet)
	  computeTime();
	time += amount * (60 * 1000L);
	areFieldsSet = false;
	break;
      case SECOND:
	if (!isTimeSet)
	  computeTime();
	time += amount * (1000L);
	areFieldsSet = false;
	break;
      case MILLISECOND:
	if (!isTimeSet)
	  computeTime();
	time += amount;
	areFieldsSet = false;
	break;
      case ZONE_OFFSET:
	complete();
	fields[ZONE_OFFSET] += amount;
	time -= amount;
	break;
      case DST_OFFSET:
	complete();
	fields[DST_OFFSET] += amount;
	isTimeSet = false;
	break;
      default:
	throw new IllegalArgumentException
	  ("Unknown Calendar field: " + field);
      }
  }


  /**
   * Rolls the specified time field up or down.  This means add one
   * to the specified field, but don't change the other fields.  If
   * the maximum for this field is reached, start over with the 
   * minimum value.  
   *
   * <strong>Note:</strong> There may be situation, where the other
   * fields must be changed, e.g rolling the month on May, 31. 
   * The date June, 31 is automatically converted to July, 1. 
   * This requires lenient settings.
   *
   * @param field the time field. One of the time field constants.
   * @param up the direction, true for up, false for down.
   */
  public void roll(int field, boolean up)
  {
    roll(field, up ? 1 : -1);
  }

  private void cleanUpAfterRoll(int field, int delta)
  {
    switch (field)
      {
      case ERA:
      case YEAR:
      case MONTH:
	// check that day of month is still in correct range
	if (fields[DAY_OF_MONTH] > getActualMaximum(DAY_OF_MONTH))
	  fields[DAY_OF_MONTH] = getActualMaximum(DAY_OF_MONTH);
	isTimeSet = false;
	isSet[WEEK_OF_MONTH] = false;
	isSet[DAY_OF_WEEK] = false;
	isSet[DAY_OF_WEEK_IN_MONTH] = false;
	isSet[DAY_OF_YEAR] = false;
	isSet[WEEK_OF_YEAR] = false;
	break;

      case DAY_OF_MONTH:
	isSet[WEEK_OF_MONTH] = false;
	isSet[DAY_OF_WEEK] = false;
	isSet[DAY_OF_WEEK_IN_MONTH] = false;
	isSet[DAY_OF_YEAR] = false;
	isSet[WEEK_OF_YEAR] = false;
	time += delta * (24 * 60 * 60 * 1000L);
	break;

      case WEEK_OF_MONTH:
	isSet[DAY_OF_MONTH] = false;
	isSet[DAY_OF_WEEK_IN_MONTH] = false;
	isSet[DAY_OF_YEAR] = false;
	isSet[WEEK_OF_YEAR] = false;
	time += delta * (7 * 24 * 60 * 60 * 1000L);
	break;
      case DAY_OF_WEEK_IN_MONTH:
	isSet[DAY_OF_MONTH] = false;
	isSet[WEEK_OF_MONTH] = false;
	isSet[DAY_OF_YEAR] = false;
	isSet[WEEK_OF_YEAR] = false;
	time += delta * (7 * 24 * 60 * 60 * 1000L);
	break;
      case DAY_OF_YEAR:
	isSet[MONTH] = false;
	isSet[DAY_OF_MONTH] = false;
	isSet[WEEK_OF_MONTH] = false;
	isSet[DAY_OF_WEEK_IN_MONTH] = false;
	isSet[DAY_OF_WEEK] = false;
	isSet[WEEK_OF_YEAR] = false;
	time += delta * (24 * 60 * 60 * 1000L);
	break;
      case WEEK_OF_YEAR:
	isSet[MONTH] = false;
	isSet[DAY_OF_MONTH] = false;
	isSet[WEEK_OF_MONTH] = false;
	isSet[DAY_OF_WEEK_IN_MONTH] = false;
	isSet[DAY_OF_YEAR] = false;
	time += delta * (7 * 24 * 60 * 60 * 1000L);
	break;

      case AM_PM:
	isSet[HOUR_OF_DAY] = false;
	time += delta * (12 * 60 * 60 * 1000L);
	break;
      case HOUR:
	isSet[HOUR_OF_DAY] = false;
	time += delta * (60 * 60 * 1000L);
	break;
      case HOUR_OF_DAY:
	isSet[HOUR] = false;
	isSet[AM_PM] = false;
	time += delta * (60 * 60 * 1000L);
	break;

      case MINUTE:
	time += delta * (60 * 1000L);
	break;
      case SECOND:
	time += delta * (1000L);
	break;
      case MILLISECOND:
	time += delta;
	break;
      }
  }

  /**
   * Rolls the specified time field by the given amount.  This means
   * add amount to the specified field, but don't change the other
   * fields.  If the maximum for this field is reached, start over
   * with the minimum value and vice versa for negative amounts.
   *
   * <strong>Note:</strong> There may be situation, where the other
   * fields must be changed, e.g rolling the month on May, 31. 
   * The date June, 31 is automatically corrected to June, 30.
   *
   * @param field the time field. One of the time field constants.
   * @param amount the amount by which we should roll.
   */
  public void roll(int field, int amount)
  {
    switch (field)
      {
      case DAY_OF_WEEK:
	// day of week is special: it rolls automatically
	add(field, amount);
	return;
      case ZONE_OFFSET:
      case DST_OFFSET:
	throw new IllegalArgumentException("Can't roll time zone");
      }
    complete();
    int min = getActualMinimum(field);
    int range = getActualMaximum(field) - min + 1;
    int oldval = fields[field];
    int newval = (oldval - min + range + amount) % range + min;
    if (newval < min)
      newval += range;
    fields[field] = newval;
    cleanUpAfterRoll(field, newval - oldval);
  }

  private static final int[] minimums =
      { BC,       1,  0,  0, 1,  1,   1,   SUNDAY, 1, 
        AM,  1,  0,  1,  1,   1, -(12*60*60*1000),               0 };

  private static final int[] maximums =
      { AD, 5000000, 11, 53, 5, 31, 366, SATURDAY, 5, 
        PM, 12, 23, 59, 59, 999, +(12*60*60*1000), (12*60*60*1000) };

  /**
   * Gets the smallest value that is allowed for the specified field.
   * @param field the time field. One of the time field constants.
   * @return the smallest value.
   */
  public int getMinimum(int field)
  {
    return minimums[field];
  }

  /**
   * Gets the biggest value that is allowed for the specified field.
   * @param field the time field. One of the time field constants.
   * @return the biggest value.
   */
  public int getMaximum(int field)
  {
    return maximums[field];
  }


  /**
   * Gets the greatest minimum value that is allowed for the specified field.
   * @param field the time field. One of the time field constants.
   * @return the greatest minimum value.
   */
  public int getGreatestMinimum(int field)
  {
    if (field == WEEK_OF_YEAR)
      return 1;
    return minimums[field];
  }

  /**
   * Gets the smallest maximum value that is allowed for the
   * specified field.  For example this is 28 for DAY_OF_MONTH.
   * @param field the time field. One of the time field constants.
   * @return the least maximum value.  
   * @since jdk1.2
   */
  public int getLeastMaximum(int field)
  {
    switch (field)
      {
      case WEEK_OF_YEAR:
	return 52;
      case DAY_OF_MONTH:
	return 28;
      case DAY_OF_YEAR:
	return 365;
      case DAY_OF_WEEK_IN_MONTH:
      case WEEK_OF_MONTH:
	return 4;
      default:
	return maximums[field];
      }
  }

  /**
   * Gets the actual minimum value that is allowed for the specified field.
   * This value is dependent on the values of the other fields.  Note that
   * this calls <code>complete()</code> if not enough fields are set.  This
   * can have ugly side effects.
   * @param field the time field. One of the time field constants.
   * @return the actual minimum value.
   * @since jdk1.2
   */
  public int getActualMinimum(int field)
  {
    if (field == WEEK_OF_YEAR)
      {
	int min = getMinimalDaysInFirstWeek();
	if (min == 0)
	  return 1;
	if (!areFieldsSet || !isSet[ERA] || !isSet[YEAR])
	  complete();

	int year = fields[ERA] == AD ? fields[YEAR] : 1 - fields[YEAR];
	int weekday = getWeekDay(year, min);
	if ((7 + weekday - getFirstDayOfWeek()) % 7 >= min - 1)
	  return 1;
	return 0;
      }
    return minimums[field];
  }

  /**
   * Gets the actual maximum value that is allowed for the specified field.
   * This value is dependent on the values of the other fields.  Note that
   * this calls <code>complete()</code> if not enough fields are set.  This
   * can have ugly side effects.
   * @param field the time field. One of the time field constants.
   * @return the actual maximum value.  
   */
  public int getActualMaximum(int field)
  {
    switch (field)
      {
      case WEEK_OF_YEAR:
	{
	  if (!areFieldsSet || !isSet[ERA] || !isSet[YEAR])
	    complete();
	  // This is wrong for the year that contains the gregorian change.
	  // I.e it gives the weeks in the julian year or in the gregorian
	  // year in that case.
	  int year = fields[ERA] == AD ? fields[YEAR] : 1 - fields[YEAR];
	  int lastDay = isLeapYear(year) ? 366 : 365;
	  int weekday = getWeekDay(year, lastDay);
	  int week = (lastDay + 6
		      - (7 + weekday - getFirstDayOfWeek()) % 7) / 7;

	  int minimalDays = getMinimalDaysInFirstWeek();
	  int firstWeekday = getWeekDay(year, minimalDays);
	  if (minimalDays - (7 + firstWeekday - getFirstDayOfWeek()) % 7 < 1)
	    return week + 1;
	}
	case DAY_OF_MONTH:
	{
	  if (!areFieldsSet || !isSet[MONTH])
	    complete();
	  int month = fields[MONTH];
	  // If you change this, you should also change 
	  // SimpleTimeZone.getDaysInMonth();
	  if (month == FEBRUARY)
	    {
	      if (!isSet[YEAR] || !isSet[ERA])
		complete();
	      int year = fields[ERA] == AD ? fields[YEAR] : 1 - fields[YEAR];
	      return isLeapYear(year) ? 29 : 28;
	    }
	  else if (month < AUGUST)
	    return 31 - (month & 1);
	  else
	    return 30 + (month & 1);
	}
      case DAY_OF_YEAR:
	{
	  if (!areFieldsSet || !isSet[ERA] || !isSet[YEAR])
	    complete();
	  int year = fields[ERA] == AD ? fields[YEAR] : 1 - fields[YEAR];
	  return isLeapYear(year) ? 366 : 365;
	}
      case DAY_OF_WEEK_IN_MONTH:
	{
	  // This is wrong for the month that contains the gregorian change.
	  int daysInMonth = getActualMaximum(DAY_OF_MONTH);
	  // That's black magic, I know
	  return (daysInMonth - (fields[DAY_OF_MONTH] - 1) % 7 + 6) / 7;
	}
      case WEEK_OF_MONTH:
	{
	  int daysInMonth = getActualMaximum(DAY_OF_MONTH);
	  int weekday = (daysInMonth - fields[DAY_OF_MONTH]
			 + fields[DAY_OF_WEEK] - SUNDAY) % 7 + SUNDAY;
	  return (daysInMonth + 6
		  - (7 + weekday - getFirstDayOfWeek()) % 7) / 7;
	}
      default:
	return maximums[field];
      }
  }
}