serialdate.java

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     * Returns the quarter for the specified month.
     *
     * @param code  the month code (1-12).
     *
     * @return the quarter that the month belongs to.
     */
    public static int monthCodeToQuarter(final int code) {

        switch(code) {
            case JANUARY: return 1;
            case FEBRUARY: return 1;
            case MARCH: return 1;
            case APRIL: return 2;
            case MAY: return 2;
            case JUNE: return 2;
            case JULY: return 3;
            case AUGUST: return 3;
            case SEPTEMBER: return 3;
            case OCTOBER: return 4;
            case NOVEMBER: return 4;
            case DECEMBER: return 4;
            default: throw new IllegalArgumentException(
                "SerialDate.monthCodeToQuarter: invalid month code.");
        }

    }

    /**
     * Returns a string representing the supplied month.
     * <P>
     * The string returned is the long form of the month name taken from the 
     * default locale.
     *
     * @param month  the month.
     *
     * @return a string representing the supplied month.
     */
    public static String monthCodeToString(final int month) {

        return monthCodeToString(month, false);

    }

    /**
     * Returns a string representing the supplied month.
     * <P>
     * The string returned is the long or short form of the month name taken 
     * from the default locale.
     *
     * @param month  the month.
     * @param shortened  if <code>true</code> return the abbreviation of the 
     *                   month.
     *
     * @return a string representing the supplied month.
     */
    public static String monthCodeToString(final int month, 
                                           final boolean shortened) {

        // check arguments...
        if (!isValidMonthCode(month)) {
            throw new IllegalArgumentException(
                "SerialDate.monthCodeToString: month outside valid range.");
        }

        final String[] months;

        if (shortened) {
            months = DATE_FORMAT_SYMBOLS.getShortMonths();
        }
        else {
            months = DATE_FORMAT_SYMBOLS.getMonths();
        }

        return months[month - 1];

    }

    /**
     * Converts a string to a month code.
     * <P>
     * This method will return one of the constants JANUARY, FEBRUARY, ..., 
     * DECEMBER that corresponds to the string.  If the string is not 
     * recognised, this method returns -1.
     *
     * @param s  the string to parse.
     *
     * @return <code>-1</code> if the string is not parseable, the month of the
     *         year otherwise.
     */
    public static int stringToMonthCode(String s) {

        final String[] shortMonthNames = DATE_FORMAT_SYMBOLS.getShortMonths();
        final String[] monthNames = DATE_FORMAT_SYMBOLS.getMonths();

        int result = -1;
        s = s.trim();

        // first try parsing the string as an integer (1-12)...
        try {
            result = Integer.parseInt(s);
        }
        catch (NumberFormatException e) {
            // suppress
        }

        // now search through the month names...
        if ((result < 1) || (result > 12)) {
            for (int i = 0; i < monthNames.length; i++) {
                if (s.equals(shortMonthNames[i])) {
                    result = i + 1;
                    break;
                }
                if (s.equals(monthNames[i])) {
                    result = i + 1;
                    break;
                }
            }
        }

        return result;

    }

    /**
     * Returns true if the supplied integer code represents a valid 
     * week-in-the-month, and false otherwise.
     *
     * @param code  the code being checked for validity.
     * @return <code>true</code> if the supplied integer code represents a 
     *         valid week-in-the-month.
     */
    public static boolean isValidWeekInMonthCode(final int code) {

        switch(code) {
            case FIRST_WEEK_IN_MONTH: return true;
            case SECOND_WEEK_IN_MONTH: return true;
            case THIRD_WEEK_IN_MONTH: return true;
            case FOURTH_WEEK_IN_MONTH: return true;
            case LAST_WEEK_IN_MONTH: return true;
            default: return false;
        }

    }

    /**
     * Determines whether or not the specified year is a leap year.
     *
     * @param yyyy  the year (in the range 1900 to 9999).
     *
     * @return <code>true</code> if the specified year is a leap year.
     */
    public static boolean isLeapYear(final int yyyy) {

        if ((yyyy % 4) != 0) {
            return false;
        }
        else if ((yyyy % 400) == 0) {
            return true;
        }
        else if ((yyyy % 100) == 0) {
            return false;
        }
        else {
            return true;
        }

    }

    /**
     * Returns the number of leap years from 1900 to the specified year 
     * INCLUSIVE.
     * <P>
     * Note that 1900 is not a leap year.
     *
     * @param yyyy  the year (in the range 1900 to 9999).
     *
     * @return the number of leap years from 1900 to the specified year.
     */
    public static int leapYearCount(final int yyyy) {

        final int leap4 = (yyyy - 1896) / 4;
        final int leap100 = (yyyy - 1800) / 100;
        final int leap400 = (yyyy - 1600) / 400;
        return leap4 - leap100 + leap400;

    }

    /**
     * Returns the number of the last day of the month, taking into account 
     * leap years.
     *
     * @param month  the month.
     * @param yyyy  the year (in the range 1900 to 9999).
     *
     * @return the number of the last day of the month.
     */
    public static int lastDayOfMonth(final int month, final int yyyy) {

        final int result = LAST_DAY_OF_MONTH[month];
        if (month != FEBRUARY) {
            return result;
        }
        else if (isLeapYear(yyyy)) {
            return result + 1;
        }
        else {
            return result;
        }

    }

    /**
     * Creates a new date by adding the specified number of days to the base 
     * date.
     *
     * @param days  the number of days to add (can be negative).
     * @param base  the base date.
     *
     * @return a new date.
     */
    public static SerialDate addDays(final int days, final SerialDate base) {

        final int serialDayNumber = base.toSerial() + days;
        return SerialDate.createInstance(serialDayNumber);

    }

    /**
     * Creates a new date by adding the specified number of months to the base 
     * date.
     * <P>
     * If the base date is close to the end of the month, the day on the result
     * may be adjusted slightly:  31 May + 1 month = 30 June.
     *
     * @param months  the number of months to add (can be negative).
     * @param base  the base date.
     *
     * @return a new date.
     */
    public static SerialDate addMonths(final int months, 
                                       final SerialDate base) {

        final int yy = (12 * base.getYYYY() + base.getMonth() + months - 1) 
                       / 12;
        final int mm = (12 * base.getYYYY() + base.getMonth() + months - 1) 
                       % 12 + 1;
        final int dd = Math.min(
            base.getDayOfMonth(), SerialDate.lastDayOfMonth(mm, yy)
        );
        return SerialDate.createInstance(dd, mm, yy);

    }

    /**
     * Creates a new date by adding the specified number of years to the base 
     * date.
     *
     * @param years  the number of years to add (can be negative).
     * @param base  the base date.
     *
     * @return A new date.
     */
    public static SerialDate addYears(final int years, final SerialDate base) {

        final int baseY = base.getYYYY();
        final int baseM = base.getMonth();
        final int baseD = base.getDayOfMonth();

        final int targetY = baseY + years;
        final int targetD = Math.min(
            baseD, SerialDate.lastDayOfMonth(baseM, targetY)
        );

        return SerialDate.createInstance(targetD, baseM, targetY);

    }

    /**
     * Returns the latest date that falls on the specified day-of-the-week and 
     * is BEFORE the base date.
     *
     * @param targetWeekday  a code for the target day-of-the-week.
     * @param base  the base date.
     *
     * @return the latest date that falls on the specified day-of-the-week and 
     *         is BEFORE the base date.
     */
    public static SerialDate getPreviousDayOfWeek(final int targetWeekday, 
                                                  final SerialDate base) {

        // check arguments...
        if (!SerialDate.isValidWeekdayCode(targetWeekday)) {
            throw new IllegalArgumentException(
                "Invalid day-of-the-week code."
            );
        }

        // find the date...
        final int adjust;
        final int baseDOW = base.getDayOfWeek();
        if (baseDOW > targetWeekday) {
            adjust = Math.min(0, targetWeekday - baseDOW);
        }
        else {
            adjust = -7 + Math.max(0, targetWeekday - baseDOW);
        }

        return SerialDate.addDays(adjust, base);

    }

    /**
     * Returns the earliest date that falls on the specified day-of-the-week
     * and is AFTER the base date.
     *
     * @param targetWeekday  a code for the target day-of-the-week.
     * @param base  the base date.
     *
     * @return the earliest date that falls on the specified day-of-the-week 
     *         and is AFTER the base date.
     */
    public static SerialDate getFollowingDayOfWeek(final int targetWeekday, 
                                                   final SerialDate base) {

        // check arguments...
        if (!SerialDate.isValidWeekdayCode(targetWeekday)) {
            throw new IllegalArgumentException(
                "Invalid day-of-the-week code."
            );
        }

        // find the date...
        final int adjust;
        final int baseDOW = base.getDayOfWeek();
        if (baseDOW > targetWeekday) {
            adjust = 7 + Math.min(0, targetWeekday - baseDOW);
        }
        else {
            adjust = Math.max(0, targetWeekday - baseDOW);
        }

        return SerialDate.addDays(adjust, base);
    }