Period fromUnits = Period.of(3, 10, 10);
Period fromDays = Period.ofDays(50);
Period fromMonths = Period.ofMonths(5);
Period fromYears = Period.ofYears(10);
Period fromWeeks = Period.ofWeeks(40);  //280天

LocalDate startDate = LocalDate.of(2015, 2, 20);
LocalDate endDate = LocalDate.of(2017, 1, 15);
// startDate減endDate
Period period = Period.between(startDate, endDate);

Period period = Period.parse("P2Y");       //2年
Period period = Period.parse("P2Y3M5D");   //2年3月5天
Period period = Period.parse("P1Y2M3W4D"); // 1年2月3周4天。即：1年2月25天

public final class Period
        implements ChronoPeriod, Serializable {
    //-----------------------------------------------------------------------
    /**
     * Obtains a {@code Period} from a text string such as {@code PnYnMnD}.
     * <p>
     * This will parse the string produced by {@code toString()} which is
     * based on the ISO-8601 period formats {@code PnYnMnD} and {@code PnW}.
     * <p>
     * The string starts with an optional sign, denoted by the ASCII negative
     * or positive symbol. If negative, the whole period is negated.
     * The ASCII letter "P" is next in upper or lower case.
     * There are then four sections, each consisting of a number and a suffix.
     * At least one of the four sections must be present.
     * The sections have suffixes in ASCII of "Y", "M", "W" and "D" for
     * years, months, weeks and days, accepted in upper or lower case.
     * The suffixes must occur in order.
     * The number part of each section must consist of ASCII digits.
     * The number may be prefixed by the ASCII negative or positive symbol.
     * The number must parse to an {@code int}.
     * <p>
     * The leading plus/minus sign, and negative values for other units are
     * not part of the ISO-8601 standard. In addition, ISO-8601 does not
     * permit mixing between the {@code PnYnMnD} and {@code PnW} formats.
     * Any week-based input is multiplied by 7 and treated as a number of days.
     * <p>
     * For example, the following are valid inputs:
     * <pre>
     *   "P2Y"             -- Period.ofYears(2)
     *   "P3M"             -- Period.ofMonths(3)
     *   "P4W"             -- Period.ofWeeks(4)
     *   "P5D"             -- Period.ofDays(5)
     *   "P1Y2M3D"         -- Period.of(1, 2, 3)
     *   "P1Y2M3W4D"       -- Period.of(1, 2, 25)
     *   "P-1Y2M"          -- Period.of(-1, 2, 0)
     *   "-P1Y2M"          -- Period.of(-1, -2, 0)
     * </pre>
     *
     * @param text  the text to parse, not null
     * @return the parsed period, not null
     * @throws DateTimeParseException if the text cannot be parsed to a period
     */
    public static Period parse(CharSequence text) {
        // 其他代碼
    }
 
    // 其他代碼
}

period.getYears();
period.getMonths();
period.getDays();

LocalDate startDate = LocalDate.of(2015, 2, 20);
LocalDate endDate = LocalDate.of(2017, 1, 15);
// startDate減endDate
Period period = Period.between(startDate, endDate);
// 任何一個時間單元為負數，則返回true。true：endDate早于startDate
period.isNegative()

Period period = Period.parse("P2Y3M5D");
period.plusDays(50);
period.minusMonths(2);

Period period = Period.parse("P1Y2M3D");
period.toTotalMonths(); // 14

Period period = Period.parse("P1Y2M3D");
period.getYears();  // 1
period.getMonths(); // 2
period.getDays();   // 3