java日期类Date与DateFormat源码详解

java日期类Date与DateFormat源码详解

Date类的定义

public class Date
    implements java.io.Serializable, Cloneable, Comparable
{
    private static final BaseCalendar gcal =
                                CalendarSystem.getGregorianCalendar();
    private static BaseCalendar jcal;

    private transient long fastTime;

    private transient BaseCalendar.Date cdate;

    // Initialized just before the value is used. See parse().
    private static int defaultCenturyStart;

    private static final long serialVersionUID = 7523967970034938905L;

    public Date() {
        this(System.currentTimeMillis());
    }

    public Date(long date) {
        fastTime = date;
    }

    public Object clone() {
        Date d = null;
        try {
            d = (Date)super.clone();
            if (cdate != null) {
                d.cdate = (BaseCalendar.Date) cdate.clone();
            }
        } catch (CloneNotSupportedException e) {} // Won't happen
        return d;
    }

}

无参构造函数Date()内部会自动调用System.currentTimeMills()来获取该Date对象被创建时的时间戳（long类型，代表从1970年1月1日至现在所经历的毫秒数）。

Date(long date)需要调用者手动传入时间戳，来获得一个特定时间的Date对象。fastTime作为该类的成员变量保存对象的时间戳数据，以供Date类其他函数调用。

    public long getTime() {
        return getTimeImpl();
    }

    private final long getTimeImpl() {
        if (cdate != null && !cdate.isNormalized()) {
            normalize();
        }
        return fastTime;
    }

    public void setTime(long time) {
        fastTime = time;
        cdate = null;
    }

    public boolean before(Date when) {
        return getMillisOf(this) < getMillisOf(when);
    }

    public boolean after(Date when) {
        return getMillisOf(this) > getMillisOf(when);
    }

    public boolean equals(Object obj) {
        return obj instanceof Date && getTime() == ((Date) obj).getTime();
    }

    static final long getMillisOf(Date date) {
        if (date.cdate == null || date.cdate.isNormalized()) {
            return date.fastTime;
        }
        BaseCalendar.Date d = (BaseCalendar.Date) date.cdate.clone();
        return gcal.getTime(d);
    }

    public int compareTo(Date anotherDate) {
        long thisTime = getMillisOf(this);
        long anotherTime = getMillisOf(anotherDate);
        return (thisTime> 32);
    }

    public String toString() {
        // "EEE MMM dd HH:mm:ss zzz yyyy";
        BaseCalendar.Date date = normalize();
        StringBuilder sb = new StringBuilder(28);
        int index = date.getDayOfWeek();
        if (index == BaseCalendar.SUNDAY) {
            index = 8;
        }
        convertToAbbr(sb, wtb[index]).append(' ');                        // EEE
        convertToAbbr(sb, wtb[date.getMonth() - 1 + 2 + 7]).append(' ');  // MMM
        CalendarUtils.sprintf0d(sb, date.getDayOfMonth(), 2).append(' '); // dd

        CalendarUtils.sprintf0d(sb, date.getHours(), 2).append(':');   // HH
        CalendarUtils.sprintf0d(sb, date.getMinutes(), 2).append(':'); // mm
        CalendarUtils.sprintf0d(sb, date.getSeconds(), 2).append(' '); // ss
        TimeZone zi = date.getZone();
        if (zi != null) {
            sb.append(zi.getDisplayName(date.isDaylightTime(), TimeZone.SHORT, Locale.US)); // zzz
        } else {
            sb.append("GMT");
        }
        sb.append(' ').append(date.getYear());  // yyyy
        return sb.toString();
    }

    private static final StringBuilder convertToAbbr(StringBuilder sb, String name) {
        sb.append(Character.toUpperCase(name.charAt(0)));
        sb.append(name.charAt(1)).append(name.charAt(2));
        return sb;
    }
    private final BaseCalendar.Date normalize() {
        if (cdate == null) {
            BaseCalendar cal = getCalendarSystem(fastTime);
            cdate = (BaseCalendar.Date) cal.getCalendarDate(fastTime,
                                                            TimeZone.getDefaultRef());
            return cdate;
        }

        // Normalize cdate with the TimeZone in cdate first. This is
        // required for the compatible behavior.
        if (!cdate.isNormalized()) {
            cdate = normalize(cdate);
        }

        // If the default TimeZone has changed, then recalculate the
        // fields with the new TimeZone.
        TimeZone tz = TimeZone.getDefaultRef();
        if (tz != cdate.getZone()) {
            cdate.setZone(tz);
            CalendarSystem cal = getCalendarSystem(cdate);
            cal.getCalendarDate(fastTime, cdate);
        }
        return cdate;
    }

    // fastTime and the returned data are in sync upon return.
    private final BaseCalendar.Date normalize(BaseCalendar.Date date) {
        int y = date.getNormalizedYear();
        int m = date.getMonth();
        int d = date.getDayOfMonth();
        int hh = date.getHours();
        int mm = date.getMinutes();
        int ss = date.getSeconds();
        int ms = date.getMillis();
        TimeZone tz = date.getZone();

        // If the specified year can't be handled using a long value
        // in milliseconds, GregorianCalendar is used for full
        // compatibility with underflow and overflow. This is required
        // by some JCK tests. The limits are based max year values -
        // years that can be represented by max values of d, hh, mm,
        // ss and ms. Also, let GregorianCalendar handle the default
        // cutover year so that we don't need to worry about the
        // transition here.
        if (y == 1582 || y > 280000000 || y < -280000000) {
            if (tz == null) {
                tz = TimeZone.getTimeZone("GMT");
            }
            GregorianCalendar gc = new GregorianCalendar(tz);
            gc.clear();
            gc.set(GregorianCalendar.MILLISECOND, ms);
            gc.set(y, m-1, d, hh, mm, ss);
            fastTime = gc.getTimeInMillis();
            BaseCalendar cal = getCalendarSystem(fastTime);
            date = (BaseCalendar.Date) cal.getCalendarDate(fastTime, tz);
            return date;
        }

        BaseCalendar cal = getCalendarSystem(y);
        if (cal != getCalendarSystem(date)) {
            date = (BaseCalendar.Date) cal.newCalendarDate(tz);
            date.setNormalizedDate(y, m, d).setTimeOfDay(hh, mm, ss, ms);
        }
        // Perform the GregorianCalendar-style normalization.
        fastTime = cal.getTime(date);

        // In case the normalized date requires the other calendar
        // system, we need to recalculate it using the other one.
        BaseCalendar ncal = getCalendarSystem(fastTime);
        if (ncal != cal) {
            date = (BaseCalendar.Date) ncal.newCalendarDate(tz);
            date.setNormalizedDate(y, m, d).setTimeOfDay(hh, mm, ss, ms);
            fastTime = ncal.getTime(date);
        }
        return date;
    }

    private static final BaseCalendar getCalendarSystem(int year) {
        if (year >= 1582) {
            return gcal;
        }
        return getJulianCalendar();
    }

    private static final BaseCalendar getCalendarSystem(long utc) {
        // Quickly check if the time stamp given by `utc' is the Epoch
        // or later. If it's before 1970, we convert the cutover to
        // local time to compare.
        if (utc >= 0
            || utc >= GregorianCalendar.DEFAULT_GREGORIAN_CUTOVER
                        - TimeZone.getDefaultRef().getOffset(utc)) {
            return gcal;
        }
        return getJulianCalendar();
    }

    private static final BaseCalendar getCalendarSystem(BaseCalendar.Date cdate) {
        if (jcal == null) {
            return gcal;
        }
        if (cdate.getEra() != null) {
            return jcal;
        }
        return gcal;
    }

    synchronized private static final BaseCalendar getJulianCalendar() {
        if (jcal == null) {
            jcal = (BaseCalendar) CalendarSystem.forName("julian");
        }
        return jcal;
    }

    private void writeObject(ObjectOutputStream s)
         throws IOException
    {
        s.writeLong(getTimeImpl());
    }

    private void readObject(ObjectInputStream s)
         throws IOException, ClassNotFoundException
    {
        fastTime = s.readLong();
    }

    public static Date from(Instant instant) {
        try {
            return new Date(instant.toEpochMilli());
        } catch (ArithmeticException ex) {
            throw new IllegalArgumentException(ex);
        }
    }

    public Instant toInstant() {
        return Instant.ofEpochMilli(getTime());
    }
}

Date常用函数

after(Date date)

该函数用来对比date是否比传入的参数when在时间上更晚，如果更晚则返回true，否则返回false。其中getMillisOf方法用来获取某Date对象储存的时间的时间戳。

before(Date date)

意义和上面的after()反过来

compareTo(Date date)

这个方法是为了sort（排序）方法服务的，compareTo方法的三种返回值（-1,0,1）的意义不在此赘述。此方法是通过比较两个date对象时间距离1970.1.1的毫秒数来确定谁大谁小的。

getTime()

其实就是返回保存了该Date对象时间戳的成员变量fastTime（该date对象时间距离1970.1.1的毫秒数）。

 

标注的Java类库包含两个类，一个是用来表示时间点的Date类，另一个是用来表示大家熟悉的日历表示法LocalDate类。

将时间与日历分开是一种很好的面向对象设计，通常，最好使用不同的类表示不同的概念。

public final class LocalDate
        implements Temporal, TemporalAdjuster, ChronoLocalDate, Serializable {

    /**
     * 最小的LocalDate日期 '-999999999-01-01'.
     * 表示过去很久
     */
    public static final LocalDate MIN = LocalDate.of(Year.MIN_VALUE, 1, 1);
    /**
     * 最大的LocalDate日期'+999999999-12-31'
     * 表示很久以后
     */
    public static final LocalDate MAX = LocalDate.of(Year.MAX_VALUE, 12, 31);

    /**
     * Serialization version.
     */
    private static final long serialVersionUID = 2942565459149668126L;
    /**
     * 400年是一个循环 共146097天
     */
    private static final int DAYS_PER_CYCLE = 146097;
    /**
     * 计算0000-1970年共多少天，这里倒过来算即先算2000年的再回退30年
     */
    static final long DAYS_0000_TO_1970 = (DAYS_PER_CYCLE * 5L) - (30L * 365L + 7L);

    /**
     * The year.
     */
    private final int year;
    /**
     * The month-of-year.
     */
    private final short month;
    /**
     * The day-of-month.
     */
    private final short day;

    //-----------------------------------------------------------------------
    /**
     * 获取本地系统时钟的时区
     */
    public static LocalDate now() {
        return now(Clock.systemDefaultZone());
    }

    /**
     * 使用特定时区
     */
    public static LocalDate now(ZoneId zone) {
        return now(Clock.system(zone));
    }

    /**
     * 获取当前日期，传入参数clock
     */
    public static LocalDate now(Clock clock) {
        Objects.requireNonNull(clock, "clock");
        // inline to avoid creating object and Instant checks
        final Instant now = clock.instant();  // called once
        ZoneOffset offset = clock.getZone().getRules().getOffset(now);
        long epochSec = now.getEpochSecond() + offset.getTotalSeconds();  // overflow caught later
        long epochDay = Math.floorDiv(epochSec, SECONDS_PER_DAY);
        return LocalDate.ofEpochDay(epochDay);
    }

    //-----------------------------------------------------------------------
    /**
     *用特定的年月日返回LocalDate,这里月份是Month类型，也就是英文的JUNE,MAY那些
     */
    public static LocalDate of(int year, Month month, int dayOfMonth) {
        YEAR.checkValidValue(year);
        Objects.requireNonNull(month, "month");
        DAY_OF_MONTH.checkValidValue(dayOfMonth);
        return create(year, month.getValue(), dayOfMonth);
    }

    /**
     *用特定的年月日返回LocalDate
     */
    public static LocalDate of(int year, int month, int dayOfMonth) {
        YEAR.checkValidValue(year);
        MONTH_OF_YEAR.checkValidValue(month);
        DAY_OF_MONTH.checkValidValue(dayOfMonth);
        return create(year, month, dayOfMonth);
    }

    //-----------------------------------------------------------------------
    /**
     *用年和一年中的第几天来返回LocalDate
     */
    public static LocalDate ofYearDay(int year, int dayOfYear) {
        YEAR.checkValidValue(year);
        DAY_OF_YEAR.checkValidValue(dayOfYear);
        boolean leap = IsoChronology.INSTANCE.isLeapYear(year);
        if (dayOfYear == 366 && leap == false) {
            throw new DateTimeException("Invalid date 'DayOfYear 366' as '" + year + "' is not a leap year");
        }
        Month moy = Month.of((dayOfYear - 1) / 31 + 1);
        int monthEnd = moy.firstDayOfYear(leap) + moy.length(leap) - 1;
        if (dayOfYear > monthEnd) {
            moy = moy.plus(1);
        }
        int dom = dayOfYear - moy.firstDayOfYear(leap) + 1;
        return new LocalDate(year, moy.getValue(), dom);
    }

    //-----------------------------------------------------------------------
    /**
     * 用纪元时间来返回LocalDate。就是从1970-01-01
     */
    public static LocalDate ofEpochDay(long epochDay) {
        long zeroDay = epochDay + DAYS_0000_TO_1970;
        // find the march-based year
        zeroDay -= 60;  // adjust to 0000-03-01 so leap day is at end of four year cycle
        long adjust = 0;
        if (zeroDay < 0) {
            // adjust negative years to positive for calculation
            long adjustCycles = (zeroDay + 1) / DAYS_PER_CYCLE - 1;
            adjust = adjustCycles * 400;
            zeroDay += -adjustCycles * DAYS_PER_CYCLE;
        }
        long yearEst = (400 * zeroDay + 591) / DAYS_PER_CYCLE;
        long doyEst = zeroDay - (365 * yearEst + yearEst / 4 - yearEst / 100 + yearEst / 400);
        if (doyEst < 0) {
            // fix estimate
            yearEst--;
            doyEst = zeroDay - (365 * yearEst + yearEst / 4 - yearEst / 100 + yearEst / 400);
        }
        yearEst += adjust;  // reset any negative year
        int marchDoy0 = (int) doyEst;

        // convert march-based values back to january-based
        int marchMonth0 = (marchDoy0 * 5 + 2) / 153;
        int month = (marchMonth0 + 2) % 12 + 1;
        int dom = marchDoy0 - (marchMonth0 * 306 + 5) / 10 + 1;
        yearEst += marchMonth0 / 10;

        // check year now we are certain it is correct
        int year = YEAR.checkValidIntValue(yearEst);
        return new LocalDate(year, month, dom);
    }

    //-----------------------------------------------------------------------
    /**
     * 
     */
    public static LocalDate from(TemporalAccessor temporal) {
        Objects.requireNonNull(temporal, "temporal");
        LocalDate date = temporal.query(TemporalQueries.localDate());
        if (date == null) {
            throw new DateTimeException("Unable to obtain LocalDate from TemporalAccessor: " +
                    temporal + " of type " + temporal.getClass().getName());
        }
        return date;
    }

    //-----------------------------------------------------------------------
    /**
     * 解析像 {@code 2007-12-03} 格式的为LocalDate.实际底层封装了DateTimeFormatter.ISO_LOCAL_DATE格式也就是2007-12-03这种
     */
    public static LocalDate parse(CharSequence text) {
        return parse(text, DateTimeFormatter.ISO_LOCAL_DATE);
    }

    /**
     * 传入一直预定义的DateTimeFormatter格式，进行解析返回LocalDate.可查看相关
     */
    public static LocalDate parse(CharSequence text, DateTimeFormatter formatter) {
        Objects.requireNonNull(formatter, "formatter");
        return formatter.parse(text, LocalDate::from);
    }

    //-----------------------------------------------------------------------
    /**
     *私有方法返回传入年月日参数的LocalDate
     */
    private static LocalDate create(int year, int month, int dayOfMonth) {
        if (dayOfMonth > 28) {
            int dom = 31;
            switch (month) {
                case 2:
                    dom = (IsoChronology.INSTANCE.isLeapYear(year) ? 29 : 28);
                    break;
                case 4:
                case 6:
                case 9:
                case 11:
                    dom = 30;
                    break;
            }
            if (dayOfMonth > dom) {
                if (dayOfMonth == 29) {
                    throw new DateTimeException("Invalid date 'February 29' as '" + year + "' is not a leap year");
                } else {
                    throw new DateTimeException("Invalid date '" + Month.of(month).name() + " " + dayOfMonth + "'");
                }
            }
        }
        return new LocalDate(year, month, dayOfMonth);
    }

    /**
     * 判断传递的日期是否合理
     */
    private static LocalDate resolvePreviousValid(int year, int month, int day) {
        switch (month) {
            case 2:
                day = Math.min(day, IsoChronology.INSTANCE.isLeapYear(year) ? 29 : 28);
                break;
            case 4:
            case 6:
            case 9:
            case 11:
                day = Math.min(day, 30);
                break;
        }
        return new LocalDate(year, month, day);
    }

    /**
     * 私有的构造函数
     */
    private LocalDate(int year, int month, int dayOfMonth) {
        this.year = year;
        this.month = (short) month;
        this.day = (short) dayOfMonth;
    }

    //-----------------------------------------------------------------------
    /**
     * 检查特定的变量是否被支持，以下是支持的种类：
     * 

     * 
{@code DAY_OF_WEEK}
     * 
{@code ALIGNED_DAY_OF_WEEK_IN_MONTH}
     * 
{@code ALIGNED_DAY_OF_WEEK_IN_YEAR}
     * 
{@code DAY_OF_MONTH}
     * 
{@code DAY_OF_YEAR}
     * 
{@code EPOCH_DAY}
     * 
{@code ALIGNED_WEEK_OF_MONTH}
     * 
{@code ALIGNED_WEEK_OF_YEAR}
     * 
{@code MONTH_OF_YEAR}
     * 
{@code PROLEPTIC_MONTH}
     * 
{@code YEAR_OF_ERA}
     * 
{@code YEAR}
     * 
{@code ERA}
     * 
     *对于非以上种类返回false
     */
    @Override  // override for Javadoc
    public boolean isSupported(TemporalField field) {
        return ChronoLocalDate.super.isSupported(field);
    }

    /**
     * 检查特定的unit是否支持，如果不支持在进行plus，minus方法时会抛出异常
     * 支持的单元有：
     * 

     * 
{@code DAYS}
     * 
{@code WEEKS}
     * 
{@code MONTHS}
     * 
{@code YEARS}
     * 
{@code DECADES}
     * 
{@code CENTURIES}
     * 
{@code MILLENNIA}
     * 
{@code ERAS}
     * 
     * 其他类型会返回false
     */
    @Override  // override for Javadoc
    public boolean isSupported(TemporalUnit unit) {
        return ChronoLocalDate.super.isSupported(unit);
    }

    //-----------------------------------------------------------------------
    /**
     * 获取特定变量的合法值
     */
    @Override
    public ValueRange range(TemporalField field) {
        if (field instanceof ChronoField) {
            ChronoField f = (ChronoField) field;
            if (f.isDateBased()) {
                switch (f) {
                    case DAY_OF_MONTH: return ValueRange.of(1, lengthOfMonth());
                    case DAY_OF_YEAR: return ValueRange.of(1, lengthOfYear());
                    case ALIGNED_WEEK_OF_MONTH: return ValueRange.of(1, getMonth() == Month.FEBRUARY && isLeapYear() == false ? 4 : 5);
                    case YEAR_OF_ERA:
                        return (getYear() = 1 ? year : 1 - year);
            case YEAR: return year;
            case ERA: return (year >= 1 ? 1 : 0);
        }
        throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
    }

    private long getProlepticMonth() {
        return (year * 12L + month - 1);
    }

    //-----------------------------------------------------------------------
    /**
     * 获取数据的年表，ISO日历系统标准
     */
    @Override
    public IsoChronology getChronology() {
        return IsoChronology.INSTANCE;
    }

    /**
     * 获取时间的era，像BE.AD这些（公元，公元前...）
     */
    @Override // override for Javadoc
    public Era getEra() {
        return ChronoLocalDate.super.getEra();
    }

    /**
     * 获取年
     */
    public int getYear() {
        return year;
    }

    /**
     * 获取月份
     */
    public int getMonthValue() {
        return month;
    }

    /**
     * 获取英文的那种月份
     */
    public Month getMonth() {
        return Month.of(month);
    }

    /**
     * 获取日
     */
    public int getDayOfMonth() {
        return day;
    }

    /**
     * 获取一年中的第几天
     */
    public int getDayOfYear() {
        return getMonth().firstDayOfYear(isLeapYear()) + day - 1;
    }

    /**
     * 获取1周中的第几天
     */
    public DayOfWeek getDayOfWeek() {
        int dow0 = (int)Math.floorMod(toEpochDay() + 3, 7);
        return DayOfWeek.of(dow0 + 1);
    }

    //-----------------------------------------------------------------------
    /**
     * 判断是否是闰年
     */
    @Override // override for Javadoc and performance
    public boolean isLeapYear() {
        return IsoChronology.INSTANCE.isLeapYear(year);
    }

    /**
     * 返回月份的长度
     */
    @Override
    public int lengthOfMonth() {
        switch (month) {
            case 2:
                return (isLeapYear() ? 29 : 28);
            case 4:
            case 6:
            case 9:
            case 11:
                return 30;
            default:
                return 31;
        }
    }

    /**
     * 返回年的长度
    public int lengthOfYear() {
        return (isLeapYear() ? 366 : 365);
    }

    //-----------------------------------------------------------------------
    /**
     * 返回一个调整过的LocalDate类型，这些adjuster是预定义的
     */
    @Override
    public LocalDate with(TemporalAdjuster adjuster) {
        // optimizations
        if (adjuster instanceof LocalDate) {
            return (LocalDate) adjuster;
        }
        return (LocalDate) adjuster.adjustInto(this);
    }

    /**
     * 返回一个调整过的LocalDate类型，这些adjuster是预定义的，传入一个新的值
     */
    @Override
    public LocalDate with(TemporalField field, long newValue) {
        if (field instanceof ChronoField) {
            ChronoField f = (ChronoField) field;
            f.checkValidValue(newValue);
            switch (f) {
                case DAY_OF_WEEK: return plusDays(newValue - getDayOfWeek().getValue());
                case ALIGNED_DAY_OF_WEEK_IN_MONTH: return plusDays(newValue - getLong(ALIGNED_DAY_OF_WEEK_IN_MONTH));
                case ALIGNED_DAY_OF_WEEK_IN_YEAR: return plusDays(newValue - getLong(ALIGNED_DAY_OF_WEEK_IN_YEAR));
                case DAY_OF_MONTH: return withDayOfMonth((int) newValue);
                case DAY_OF_YEAR: return withDayOfYear((int) newValue);
                case EPOCH_DAY: return LocalDate.ofEpochDay(newValue);
                case ALIGNED_WEEK_OF_MONTH: return plusWeeks(newValue - getLong(ALIGNED_WEEK_OF_MONTH));
                case ALIGNED_WEEK_OF_YEAR: return plusWeeks(newValue - getLong(ALIGNED_WEEK_OF_YEAR));
                case MONTH_OF_YEAR: return withMonth((int) newValue);
                case PROLEPTIC_MONTH: return plusMonths(newValue - getProlepticMonth());
                case YEAR_OF_ERA: return withYear((int) (year >= 1 ? newValue : 1 - newValue));
                case YEAR: return withYear((int) newValue);
                case ERA: return (getLong(ERA) == newValue ? this : withYear(1 - year));
            }
            throw new UnsupportedTemporalTypeException("Unsupported field: " + field);
        }
        return field.adjustInto(this, newValue);
    }

    //-----------------------------------------------------------------------
    /**
     * 改年返回新的LocalDate
     */
    public LocalDate withYear(int year) {
        if (this.year == year) {
            return this;
        }
        YEAR.checkValidValue(year);
        return resolvePreviousValid(year, month, day);
    }

    /**
     * 改月返回新的LocalDate
     */
    public LocalDate withMonth(int month) {
        if (this.month == month) {
            return this;
        }
        MONTH_OF_YEAR.checkValidValue(month);
        return resolvePreviousValid(year, month, day);
    }

    /**
     *改日返回新的LocalDate
     */
    public LocalDate withDayOfMonth(int dayOfMonth) {
        if (this.day == dayOfMonth) {
            return this;
        }
        return of(year, month, dayOfMonth);
    }

    /**
     * 改一年中第几日返回新的LocalDate
     */
    public LocalDate withDayOfYear(int dayOfYear) {
        if (this.getDayOfYear() == dayOfYear) {
            return this;
        }
        return ofYearDay(year, dayOfYear);
    }

    //-----------------------------------------------------------------------
    /**
     * 返回新的LocalDate，在原值上进行 加 操作
     */
    @Override
    public LocalDate plus(TemporalAmount amountToAdd) {
        if (amountToAdd instanceof Period) {
            Period periodToAdd = (Period) amountToAdd;
            return plusMonths(periodToAdd.toTotalMonths()).plusDays(periodToAdd.getDays());
        }
        Objects.requireNonNull(amountToAdd, "amountToAdd");
        return (LocalDate) amountToAdd.addTo(this);
    }

    /**
     * 返回新的LocalDate，在原值上进行 加 操作
    /
    @Override
    public LocalDate plus(long amountToAdd, TemporalUnit unit) {
        if (unit instanceof ChronoUnit) {
            ChronoUnit f = (ChronoUnit) unit;
            switch (f) {
                case DAYS: return plusDays(amountToAdd);
                case WEEKS: return plusWeeks(amountToAdd);
                case MONTHS: return plusMonths(amountToAdd);
                case YEARS: return plusYears(amountToAdd);
                case DECADES: return plusYears(Math.multiplyExact(amountToAdd, 10));
                case CENTURIES: return plusYears(Math.multiplyExact(amountToAdd, 100));
                case MILLENNIA: return plusYears(Math.multiplyExact(amountToAdd, 1000));
                case ERAS: return with(ERA, Math.addExact(getLong(ERA), amountToAdd));
            }
            throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
        }
        return unit.addTo(this, amountToAdd);
    }

    //-----------------------------------------------------------------------
    /**
     * 在原本基础上对年添加传入值后返回一个LocalDate
     */
    public LocalDate plusYears(long yearsToAdd) {
        if (yearsToAdd == 0) {
            return this;
        }
        int newYear = YEAR.checkValidIntValue(year + yearsToAdd);  // safe overflow
        return resolvePreviousValid(newYear, month, day);
    }

    /**
     * 在原本基础上对月添加传入值后返回一个LocalDate
     */
    public LocalDate plusMonths(long monthsToAdd) {
        if (monthsToAdd == 0) {
            return this;
        }
        long monthCount = year * 12L + (month - 1);
        long calcMonths = monthCount + monthsToAdd;  // safe overflow
        int newYear = YEAR.checkValidIntValue(Math.floorDiv(calcMonths, 12));
        int newMonth = (int)Math.floorMod(calcMonths, 12) + 1;
        return resolvePreviousValid(newYear, newMonth, day);
    }

    /**
     * 在原本基础上对周添加传入值后返回一个LocalDate，底层调用的是加7天
     */
    public LocalDate plusWeeks(long weeksToAdd) {
        return plusDays(Math.multiplyExact(weeksToAdd, 7));
    }

    /**
     * 在原本基础上对日添加传入值后返回一个LocalDate
     */
    public LocalDate plusDays(long daysToAdd) {
        if (daysToAdd == 0) {
            return this;
        }
        long mjDay = Math.addExact(toEpochDay(), daysToAdd);
        return LocalDate.ofEpochDay(mjDay);
    }

    //-----------------------------------------------------------------------
    /**
     * 减，底层调用的还是plus相关的方法，传入的是实际上是负值
     */
    @Override
    public LocalDate minus(TemporalAmount amountToSubtract) {
        if (amountToSubtract instanceof Period) {
            Period periodToSubtract = (Period) amountToSubtract;
            return minusMonths(periodToSubtract.toTotalMonths()).minusDays(periodToSubtract.getDays());
        }
        Objects.requireNonNull(amountToSubtract, "amountToSubtract");
        return (LocalDate) amountToSubtract.subtractFrom(this);
    }

    @Override
    public LocalDate minus(long amountToSubtract, TemporalUnit unit) {
        return (amountToSubtract == Long.MIN_VALUE ? plus(Long.MAX_VALUE, unit).plus(1, unit) : plus(-amountToSubtract, unit));
    }


    public LocalDate minusYears(long yearsToSubtract) {
        return (yearsToSubtract == Long.MIN_VALUE ? plusYears(Long.MAX_VALUE).plusYears(1) : plusYears(-yearsToSubtract));
    }

    public LocalDate minusMonths(long monthsToSubtract) {
        return (monthsToSubtract == Long.MIN_VALUE ? plusMonths(Long.MAX_VALUE).plusMonths(1) : plusMonths(-monthsToSubtract));
    }

    public LocalDate minusWeeks(long weeksToSubtract) {
        return (weeksToSubtract == Long.MIN_VALUE ? plusWeeks(Long.MAX_VALUE).plusWeeks(1) : plusWeeks(-weeksToSubtract));
    }

    public LocalDate minusDays(long daysToSubtract) {
        return (daysToSubtract == Long.MIN_VALUE ? plusDays(Long.MAX_VALUE).plusDays(1) : plusDays(-daysToSubtract));
    }

    //-----------------------------------------------------------------------
    /**
     * 特定查询
     */
    @SuppressWarnings("unchecked")
    @Override
    public  R query(TemporalQuery query) {
        if (query == TemporalQueries.localDate()) {
            return (R) this;
        }
        return ChronoLocalDate.super.query(query);
    }

    /**
     * 
     * 
     *   // 下面两种是相同的，但推荐第二种
     *   temporal = thisLocalDate.adjustInto(temporal);
     *   temporal = temporal.with(thisLocalDate);
     * 
     *
     */
    @Override  // override for Javadoc
    public Temporal adjustInto(Temporal temporal) {
        return ChronoLocalDate.super.adjustInto(temporal);
    }

    @Override
    public long until(Temporal endExclusive, TemporalUnit unit) {
        LocalDate end = LocalDate.from(endExclusive);
        if (unit instanceof ChronoUnit) {
            switch ((ChronoUnit) unit) {
                case DAYS: return daysUntil(end);
                case WEEKS: return daysUntil(end) / 7;
                case MONTHS: return monthsUntil(end);
                case YEARS: return monthsUntil(end) / 12;
                case DECADES: return monthsUntil(end) / 120;
                case CENTURIES: return monthsUntil(end) / 1200;
                case MILLENNIA: return monthsUntil(end) / 12000;
                case ERAS: return end.getLong(ERA) - getLong(ERA);
            }
            throw new UnsupportedTemporalTypeException("Unsupported unit: " + unit);
        }
        return unit.between(this, end);
    }

    long daysUntil(LocalDate end) {
        return end.toEpochDay() - toEpochDay();  // no overflow
    }

    private long monthsUntil(LocalDate end) {
        long packed1 = getProlepticMonth() * 32L + getDayOfMonth();  // no overflow
        long packed2 = end.getProlepticMonth() * 32L + end.getDayOfMonth();  // no overflow
        return (packed2 - packed1) / 32;
    }

    @Override
    public Period until(ChronoLocalDate endDateExclusive) {
        LocalDate end = LocalDate.from(endDateExclusive);
        long totalMonths = end.getProlepticMonth() - this.getProlepticMonth();  // safe
        int days = end.day - this.day;
        if (totalMonths > 0 && days < 0) {
            totalMonths--;
            LocalDate calcDate = this.plusMonths(totalMonths);
            days = (int) (end.toEpochDay() - calcDate.toEpochDay());  // safe
        } else if (totalMonths < 0 && days > 0) {
            totalMonths++;
            days -= end.lengthOfMonth();
        }
        long years = totalMonths / 12;  // safe
        int months = (int) (totalMonths % 12);  // safe
        return Period.of(Math.toIntExact(years), months, days);
    }

    /**
     * 用特定的格式格式化日期
     */
    @Override  // override for Javadoc and performance
    public String format(DateTimeFormatter formatter) {
        Objects.requireNonNull(formatter, "formatter");
        return formatter.format(this);
    }

    //-----------------------------------------------------------------------
    /**
     * 结合时间格式LocalTime，返回一个LocalDateTime对象
     */
    @Override
    public LocalDateTime atTime(LocalTime time) {
        return LocalDateTime.of(this, time);
    }

    /**
     * 结合时间格式： 时 分，返回一个LocalDateTime对象
     */
    public LocalDateTime atTime(int hour, int minute) {
        return atTime(LocalTime.of(hour, minute));
    }

    /**
     * 结合时分秒，返回一个LocalDateTime对象
     */
    public LocalDateTime atTime(int hour, int minute, int second) {
        return atTime(LocalTime.of(hour, minute, second));
    }

    /**
     * 结合时分秒 纳秒，返回一个LocalDateTime对象
     */
    public LocalDateTime atTime(int hour, int minute, int second, int nanoOfSecond) {
        return atTime(LocalTime.of(hour, minute, second, nanoOfSecond));
    }

    /**
     * 结合一个OffsetTime格式，返回一个OffsetTime对象。OffsetTime表示具有相对于UTC的固定区偏移的时间。
     */
    public OffsetDateTime atTime(OffsetTime time) {
        return OffsetDateTime.of(LocalDateTime.of(this, time.toLocalTime()), time.getOffset());
    }

    /**
     * 结合午夜时间0点返回一个LocalDateTime对象
     */
    public LocalDateTime atStartOfDay() {
        return LocalDateTime.of(this, LocalTime.MIDNIGHT);
    }

    /**
     * 传入时区id，返回一个ZonedDateTime
     */
    public ZonedDateTime atStartOfDay(ZoneId zone) {
        Objects.requireNonNull(zone, "zone");
        // need to handle case where there is a gap from 11:30 to 00:30
        // standard ZDT factory would result in 01:00 rather than 00:30
        LocalDateTime ldt = atTime(LocalTime.MIDNIGHT);
        if (zone instanceof ZoneOffset == false) {
            ZoneRules rules = zone.getRules();
            ZoneOffsetTransition trans = rules.getTransition(ldt);
            if (trans != null && trans.isGap()) {
                ldt = trans.getDateTimeAfter();
            }
        }
        return ZonedDateTime.of(ldt, zone);
    }

    //-----------------------------------------------------------------------
    @Override
    public long toEpochDay() {
        long y = year;
        long m = month;
        long total = 0;
        total += 365 * y;
        if (y >= 0) {
            total += (y + 3) / 4 - (y + 99) / 100 + (y + 399) / 400;
        } else {
            total -= y / -4 - y / -100 + y / -400;
        }
        total += ((367 * m - 362) / 12);
        total += day - 1;
        if (m > 2) {
            total--;
            if (isLeapYear() == false) {
                total--;
            }
        }
        return total - DAYS_0000_TO_1970;
    }

    //-----------------------------------------------------------------------
    /**
     * 和另一个日期的年月日进行比较判断
     */
    @Override  // override for Javadoc and performance
    public int compareTo(ChronoLocalDate other) {
        if (other instanceof LocalDate) {
            return compareTo0((LocalDate) other);
        }
        return ChronoLocalDate.super.compareTo(other);
    }

    int compareTo0(LocalDate otherDate) {
        int cmp = (year - otherDate.year);
        if (cmp == 0) {
            cmp = (month - otherDate.month);
            if (cmp == 0) {
                cmp = (day - otherDate.day);
            }
        }
        return cmp;
    }

    /**
     * 判断一个日期是否在另一个之后
     */
    @Override  // override for Javadoc and performance
    public boolean isAfter(ChronoLocalDate other) {
        if (other instanceof LocalDate) {
            return compareTo0((LocalDate) other) > 0;
        }
        return ChronoLocalDate.super.isAfter(other);
    }

    /**
     * 判断一个日期是否在另一个日期之前
     */
    @Override  // override for Javadoc and performance
    public boolean isBefore(ChronoLocalDate other) {
        if (other instanceof LocalDate) {
            return compareTo0((LocalDate) other) < 0;
        }
        return ChronoLocalDate.super.isBefore(other);
    }

    /**
     * 判断一个日期是否在另一个之前
     */
    @Override  // override for Javadoc and performance
    public boolean isEqual(ChronoLocalDate other) {
        if (other instanceof LocalDate) {
            return compareTo0((LocalDate) other) == 0;
        }
        return ChronoLocalDate.super.isEqual(other);
    }

    //-----------------------------------------------------------------------
    /**
     * 重写object的equals方法，判断与对象obj是否相等
     */
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj instanceof LocalDate) {
            return compareTo0((LocalDate) obj) == 0;
        }
        return false;
    }

    /**
     * 重写object的hashcode方法
     */
    @Override
    public int hashCode() {
        int yearValue = year;
        int monthValue = month;
        int dayValue = day;
        return (yearValue & 0xFFFFF800) ^ ((yearValue