Review

class DateUtils {
    /**
     * Adds to a date returning a new object.
     * The original date object is unchanged.
     *
     * @param date  the date, not null
     * @param calendarField  the calendar field to add to
     * @param amount  the amount to add, may be negative
     * @return the new date object with the amount added
     * @throws IllegalArgumentException if the date is null
     * @deprecated Will become privately scoped in 3.0
     */
    public static Date add(Date date, int calendarField, int amount) {
        if (date == null) {
            throw new IllegalArgumentException("The date must not be null");
        }
        Calendar c = Calendar.getInstance();
        c.setTime(date);
        c.add(calendarField, amount);
        return c.getTime();
    }

}