深入学习java源码之Date.before()与Date.clone()

源码之Date.before()与Date.clone()"/>

深入学习java源码之Date.before()与Date.clone()

深入学习java源码之Date.before()与Date.clone()

类 Date 表示特定的瞬间，精确到毫秒。

在 JDK 1.1 之前，类 Date 有两个其他的函数。它允许把日期解释为年、月、日、小时、分钟和秒值。它也允许格式化和分析日期字符串。不过，这些函数的 API 不易于实现国际化。从 JDK 1.1 开始，应该使用 Calendar 类实现日期和时间字段之间转换，使用 DateFormat 类来格式化和分析日期字符串。Date 中的相应方法已废弃。

尽管 Date 类打算反映协调世界时 (UTC)，但无法做到如此准确，这取决于 Java 虚拟机的主机环境。当前几乎所有操作系统都假定 1 天 = 24 × 60 × 60 = 86400 秒。但对于 UTC，大约每一两年出现一次额外的一秒，称为“闰秒”。闰秒始终作为当天的最后一秒增加，并且始终在 12 月 31 日或 6 月 30 日增加。例如，1995 年的最后一分钟是 61 秒，因为增加了闰秒。大多数计算机时钟不是特别的准确，因此不能反映闰秒的差别。

一些计算机标准是按照格林威治标准时 (GMT) 定义的，格林威治标准时和世界时 (UT) 是相等的。GMT 是标准的“民间”名称；UT 是相同标准的“科学”名称。UTC 和 UT 的区别是：UTC 是基于原子时钟的，UT 是基于天体观察的，两者在实际应用中难分轩轾。因为地球的旋转不是均匀的（它以复杂的方式减速和加速），所以 UT 始终不是均匀地流过。闰秒是根据需要引入 UTC 的，以便把 UTC 保持在 UT1 的 0.9 秒之内，UT1 是应用了某些更正的 UT 版本。

fastTime:当前时间的毫秒表示(从1970.1.1开始算)

Date():用当前时间的毫秒数来初始化fastTime；

public Date() {this(System.currentTimeMillis());}
public Date(long date) {fastTime = date;}

clone() :返回该Date对象的一个’副本’(虽然返回是Object，不过可以转成Date)；

clone方法是用来复制一个对象。不同于“=”。

对于值类型的数据是可以通过“=”来实现复制的。但是对于引用类型的对象，“=”只能复制其内存地址，使对象的引用指向同一个对象，而不会创建新的对象。clone则可以创建与原来对象相同的对象。举个例子：

Car c1 = new Car();
Car c2 = c1;

这两句事实上只创建了一个对象。只不过c1和c2指向了同一个对象。二者指向的还是同一块内存，所以任何一个引用对内存的操作都直接反映到另一个引用上。

Car c1 = new Car();
Car c2 = c1.clone();

那么就有了两个对象，而且这两个对象的内容是一样的。（所有的属性值相同）

浅拷贝方式，也就是它并不会把对象所有属性全部拷贝一份，而是有选择性的拷贝，拷贝规则如下：

1、基本类型

如果变量是基本类型，则拷贝其值，比如：int、float、long等。

2、String字符串

这个比较特殊，拷贝的是地址，是个引用，但是在修改的时候，它会从字符串池（String Pool）中重新生成新的字符串，原有的字符串对象保持不变，此处可以认为String是个基本类型。

3、对象

如果变量时一个实例对象，则拷贝地址引用，也就是说此时新拷贝出的对象与原有对象共享该实例变量，不受访问权限的限制。这在Java中很疯狂，因为它突破了访问权限的定义，一个private修饰的变量，竟然可以被两个实例对象访问。

关于clone方法的浅拷贝的一个demo，可以看出虽然是两个不同的ShallowCopy对象，但是对于他们的非基本数据类型的成员变量是属于同一个引用。因此是浅拷贝

import java.util.Date;public class ShallowCopy implements Cloneable {private Date begin;public Date getBegin(){return this.begin;}public void setBegin(Date d){this.begin = d;}public Object clone(){Object obj = null;try{obj = super.clone();}catch(CloneNotSupportedException ex){ex.printStackTrace();}return obj;}public static void main(String[] args) {Date date = new Date(10000L);ShallowCopy copy = new ShallowCopy();copy.setBegin(date);ShallowCopy copy2 = (ShallowCopy) copy.clone();System.out.println(copy.getBegin() + "\n" + copy2.getBegin() + "\n" + (copy == copy2));date.setTime(100000000L);;System.out.println(copy.getBegin() + "\n" + copy2.getBegin() + "\n" + (copy == copy2));}
//    Thu Jan 01 08:00:10 CST 1970
//    Thu Jan 01 08:00:10 CST 1970
//    false
//    Fri Jan 02 11:46:40 CST 1970
//    Fri Jan 02 11:46:40 CST 1970
//    false
}

相比深拷贝，拷贝对象的同时，又进行了对成员对象进行了深拷贝。

import java.util.Date;public class DeepCopy implements Cloneable{private Date begin;public Date getBegin(){return this.begin;}public void setBegin(Date d){this.begin = d;}public Object clone(){DeepCopy obj = null;try{obj = (DeepCopy)super.clone();}catch(CloneNotSupportedException e){e.printStackTrace();}obj.setBegin((Date)this.getBegin().clone());return obj;}public static void main(String[] args) {Date date = new Date(10000L);DeepCopy copy = new DeepCopy();copy.setBegin(date);DeepCopy copy2 = (DeepCopy) copy.clone();System.out.println(copy.getBegin() + "\n" + copy2.getBegin() + "\n" + (copy == copy2));date.setTime(100000000L);System.out.println(copy.getBegin() + "\n" + copy2.getBegin() + "\n" + (copy == copy2));}
//    Thu Jan 01 08:00:10 CST 1970
//    Thu Jan 01 08:00:10 CST 1970
//    false
//    Fri Jan 02 11:46:40 CST 1970
//    Thu Jan 01 08:00:10 CST 1970
//    false
}

before(Date when)/after(Date when):与when比较是早(before)还是晚(after)（相当于小于号和大于号）。

compareTo(Date anotherDate):定义比较两个Date对象的规则（通过fastTime值的大小）

案例:计算星期几

package comtenmon.utils;import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;public class DateUtil {public static Date getLastWeekMonday(Date date) {Calendar cal = Calendar.getInstance();cal.setTime(getThisWeekMonday(date));cal.add(Calendar.DATE, -7);return cal.getTime();}public static Date getLastWeekFriday(Date date){Calendar cal = Calendar.getInstance();cal.setTime(getThisWeekMonday(date));cal.add(Calendar.DATE, -3);return cal.getTime();}public static String getLastWeekFridayStr(Date date){SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");Calendar cal = Calendar.getInstance();cal.setTime(getThisWeekMonday(date));cal.add(Calendar.DATE, -3);return sdf.format(cal.getTime());}public static String getLastWeekMondayStr(Date date){SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");Calendar cal = Calendar.getInstance();cal.setTime(getThisWeekMonday(date));cal.add(Calendar.DATE, -7);return sdf.format(cal.getTime());}public static Date getThisWeekMonday(Date date) {Calendar cal = Calendar.getInstance();cal.setTime(date);// 获得当前日期是一个星期的第几天int dayWeek = cal.get(Calendar.DAY_OF_WEEK);if (1 == dayWeek) {cal.add(Calendar.DAY_OF_MONTH, -1);}// 设置一个星期的第一天，按中国的习惯一个星期的第一天是星期一cal.setFirstDayOfWeek(Calendar.MONDAY);// 获得当前日期是一个星期的第几天int day = cal.get(Calendar.DAY_OF_WEEK);// 根据日历的规则，给当前日期减去星期几与一个星期第一天的差值cal.add(Calendar.DATE, cal.getFirstDayOfWeek() - day);return cal.getTime();}
}

               Date now = new Date();//判断本周是星期几：1是星期日、2是星期一、3是星期二、4是星期三、5是星期四、6是星期五、7是星期六int weekDay = DateUtil.getDayofweek(now);//上周一日期String lastMonday = DateUtil.getWeekDayOfDate(now, -7);//上周二日期String lastThuesDay = DateUtil.getWeekDayOfDate(now, -6);//上周三String lastWednesday = DateUtil.getWeekDayOfDate(now, -5);//上周四日期String lastThursDay = DateUtil.getWeekDayOfDate(now, -4);//上周五String lastFriDay = DateUtil.getWeekDayOfDate(now, -3);//本周周一String thisMonday = DateUtil.getThisWeekMondayStr(now);//本周周二String thisThuesDay = DateUtil.getWeekDayOfDate(now, 1);//本周三String thisWednesday = DateUtil.getWeekDayOfDate(now, 2);//本周四String thisThursDay = DateUtil.getWeekDayOfDate(now, 3);//本周五String thisFriDay = DateUtil.getWeekDayOfDate(now, 4);List<LinkedHashMap<String, Object>>  allDataList = new ArrayList<LinkedHashMap<String, Object>>();

java源码

package java.util;import java.text.DateFormat;
import java.time.LocalDate;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.lang.ref.SoftReference;
import java.time.Instant;
import sun.util.calendar.BaseCalendar;
import sun.util.calendar.CalendarDate;
import sun.util.calendar.CalendarSystem;
import sun.util.calendar.CalendarUtils;
import sun.util.calendar.Era;
import sun.util.calendar.Gregorian;
import sun.util.calendar.ZoneInfo;public class Dateimplements java.io.Serializable, Cloneable, Comparable<Date>
{private static final BaseCalendar gcal =CalendarSystem.getGregorianCalendar();private static BaseCalendar jcal;private transient long fastTime;private transient BaseCalendar.Date cdate;private static int defaultCenturyStart;private static final long serialVersionUID = 7523967970034938905L;	public Date() {this(System.currentTimeMillis());}	public Date(long date) {fastTime = date;}	@Deprecatedpublic Date(int year, int month, int date) {this(year, month, date, 0, 0, 0);}	@Deprecatedpublic Date(int year, int month, int date, int hrs, int min) {this(year, month, date, hrs, min, 0);}@Deprecatedpublic Date(int year, int month, int date, int hrs, int min, int sec) {int y = year + 1900;// month is 0-based. So we have to normalize month to support Long.MAX_VALUE.if (month >= 12) {y += month / 12;month %= 12;} else if (month < 0) {y += CalendarUtils.floorDivide(month, 12);month = CalendarUtils.mod(month, 12);}BaseCalendar cal = getCalendarSystem(y);cdate = (BaseCalendar.Date) cal.newCalendarDate(TimeZone.getDefaultRef());cdate.setNormalizedDate(y, month + 1, date).setTimeOfDay(hrs, min, sec, 0);getTimeImpl();cdate = null;}	@Deprecatedpublic Date(String s) {this(parse(s));}	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 happenreturn d;}	@Deprecatedpublic static long UTC(int year, int month, int date,int hrs, int min, int sec) {int y = year + 1900;// month is 0-based. So we have to normalize month to support Long.MAX_VALUE.if (month >= 12) {y += month / 12;month %= 12;} else if (month < 0) {y += CalendarUtils.floorDivide(month, 12);month = CalendarUtils.mod(month, 12);}int m = month + 1;BaseCalendar cal = getCalendarSystem(y);BaseCalendar.Date udate = (BaseCalendar.Date) cal.newCalendarDate(null);udate.setNormalizedDate(y, m, date).setTimeOfDay(hrs, min, sec, 0);// Use a Date instance to perform normalization. Its fastTime// is the UTC value after the normalization.Date d = new Date(0);d.normalize(udate);return d.fastTime;}	@Deprecatedpublic static long parse(String s) {int year = Integer.MIN_VALUE;int mon = -1;int mday = -1;int hour = -1;int min = -1;int sec = -1;int millis = -1;int c = -1;int i = 0;int n = -1;int wst = -1;int tzoffset = -1;int prevc = 0;syntax:{if (s == null)break syntax;int limit = s.length();while (i < limit) {c = s.charAt(i);i++;if (c <= ' ' || c == ',')continue;if (c == '(') { // skip commentsint depth = 1;while (i < limit) {c = s.charAt(i);i++;if (c == '(') depth++;else if (c == ')')if (--depth <= 0)break;}continue;}if ('0' <= c && c <= '9') {n = c - '0';while (i < limit && '0' <= (c = s.charAt(i)) && c <= '9') {n = n * 10 + c - '0';i++;}if (prevc == '+' || prevc == '-' && year != Integer.MIN_VALUE) {// timezone offsetif (n < 24)n = n * 60; // EG. "GMT-3"elsen = n % 100 + n / 100 * 60; // eg "GMT-0430"if (prevc == '+')   // plus means east of GMTn = -n;if (tzoffset != 0 && tzoffset != -1)break syntax;tzoffset = n;} else if (n >= 70)if (year != Integer.MIN_VALUE)break syntax;else if (c <= ' ' || c == ',' || c == '/' || i >= limit)// year = n < 1900 ? n : n - 1900;year = n;elsebreak syntax;else if (c == ':')if (hour < 0)hour = (byte) n;else if (min < 0)min = (byte) n;elsebreak syntax;else if (c == '/')if (mon < 0)mon = (byte) (n - 1);else if (mday < 0)mday = (byte) n;elsebreak syntax;else if (i < limit && c != ',' && c > ' ' && c != '-')break syntax;else if (hour >= 0 && min < 0)min = (byte) n;else if (min >= 0 && sec < 0)sec = (byte) n;else if (mday < 0)mday = (byte) n;// Handle two-digit years < 70 (70-99 handled above).else if (year == Integer.MIN_VALUE && mon >= 0 && mday >= 0)year = n;elsebreak syntax;prevc = 0;} else if (c == '/' || c == ':' || c == '+' || c == '-')prevc = c;else {int st = i - 1;while (i < limit) {c = s.charAt(i);if (!('A' <= c && c <= 'Z' || 'a' <= c && c <= 'z'))break;i++;}if (i <= st + 1)break syntax;int k;for (k = wtb.length; --k >= 0;)if (wtb[k].regionMatches(true, 0, s, st, i - st)) {int action = ttb[k];if (action != 0) {if (action == 1) {  // pmif (hour > 12 || hour < 1)break syntax;else if (hour < 12)hour += 12;} else if (action == 14) {  // amif (hour > 12 || hour < 1)break syntax;else if (hour == 12)hour = 0;} else if (action <= 13) {  // month!if (mon < 0)mon = (byte) (action - 2);elsebreak syntax;} else {tzoffset = action - 10000;}}break;}if (k < 0)break syntax;prevc = 0;}}if (year == Integer.MIN_VALUE || mon < 0 || mday < 0)break syntax;// Parse 2-digit years within the correct default century.if (year < 100) {synchronized (Date.class) {if (defaultCenturyStart == 0) {defaultCenturyStart = gcal.getCalendarDate().getYear() - 80;}}year += (defaultCenturyStart / 100) * 100;if (year < defaultCenturyStart) year += 100;}if (sec < 0)sec = 0;if (min < 0)min = 0;if (hour < 0)hour = 0;BaseCalendar cal = getCalendarSystem(year);if (tzoffset == -1)  { // no time zone specified, have to use localBaseCalendar.Date ldate = (BaseCalendar.Date) cal.newCalendarDate(TimeZone.getDefaultRef());ldate.setDate(year, mon + 1, mday);ldate.setTimeOfDay(hour, min, sec, 0);return cal.getTime(ldate);}BaseCalendar.Date udate = (BaseCalendar.Date) cal.newCalendarDate(null); // no time zoneudate.setDate(year, mon + 1, mday);udate.setTimeOfDay(hour, min, sec, 0);return cal.getTime(udate) + tzoffset * (60 * 1000);}// syntax errorthrow new IllegalArgumentException();}private final static String wtb[] = {"am", "pm","monday", "tuesday", "wednesday", "thursday", "friday","saturday", "sunday","january", "february", "march", "april", "may", "june","july", "august", "september", "october", "november", "december","gmt", "ut", "utc", "est", "edt", "cst", "cdt","mst", "mdt", "pst", "pdt"};private final static int ttb[] = {14, 1, 0, 0, 0, 0, 0, 0, 0,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,10000 + 0, 10000 + 0, 10000 + 0,    // GMT/UT/UTC10000 + 5 * 60, 10000 + 4 * 60,     // EST/EDT10000 + 6 * 60, 10000 + 5 * 60,     // CST/CDT10000 + 7 * 60, 10000 + 6 * 60,     // MST/MDT10000 + 8 * 60, 10000 + 7 * 60      // PST/PDT};	@Deprecatedpublic int getYear() {return normalize().getYear() - 1900;}	@Deprecatedpublic void setYear(int year) {getCalendarDate().setNormalizedYear(year + 1900);}	@Deprecatedpublic int getMonth() {return normalize().getMonth() - 1; // adjust 1-based to 0-based}	@Deprecatedpublic void setMonth(int month) {int y = 0;if (month >= 12) {y = month / 12;month %= 12;} else if (month < 0) {y = CalendarUtils.floorDivide(month, 12);month = CalendarUtils.mod(month, 12);}BaseCalendar.Date d = getCalendarDate();if (y != 0) {d.setNormalizedYear(d.getNormalizedYear() + y);}d.setMonth(month + 1); // adjust 0-based to 1-based month numbering}	@Deprecatedpublic int getDate() {return normalize().getDayOfMonth();}	@Deprecatedpublic void setDate(int date) {getCalendarDate().setDayOfMonth(date);}	@Deprecatedpublic int getDay() {return normalize().getDayOfWeek() - BaseCalendar.SUNDAY;}	@Deprecatedpublic int getHours() {return normalize().getHours();}@Deprecatedpublic void setHours(int hours) {getCalendarDate().setHours(hours);}@Deprecatedpublic int getMinutes() {return normalize().getMinutes();}@Deprecatedpublic void setMinutes(int minutes) {getCalendarDate().setMinutes(minutes);}@Deprecatedpublic int getSeconds() {return normalize().getSeconds();}@Deprecatedpublic void setSeconds(int seconds) {getCalendarDate().setSeconds(seconds);}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<anotherTime ? -1 : (thisTime==anotherTime ? 0 : 1));}public int hashCode() {long ht = this.getTime();return (int) ht ^ (int) (ht >> 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(' ');                        // EEEconvertToAbbr(sb, wtb[date.getMonth() - 1 + 2 + 7]).append(' ');  // MMMCalendarUtils.sprintf0d(sb, date.getDayOfMonth(), 2).append(' '); // ddCalendarUtils.sprintf0d(sb, date.getHours(), 2).append(':');   // HHCalendarUtils.sprintf0d(sb, date.getMinutes(), 2).append(':'); // mmCalendarUtils.sprintf0d(sb, date.getSeconds(), 2).append(' '); // ssTimeZone 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());  // yyyyreturn 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;}@Deprecatedpublic String toLocaleString() {DateFormat formatter = DateFormat.getDateTimeInstance();return formatter.format(this);}@Deprecatedpublic String toGMTString() {// d MMM yyyy HH:mm:ss 'GMT'long t = getTime();BaseCalendar cal = getCalendarSystem(t);BaseCalendar.Date date =(BaseCalendar.Date) cal.getCalendarDate(getTime(), (TimeZone)null);StringBuilder sb = new StringBuilder(32);CalendarUtils.sprintf0d(sb, date.getDayOfMonth(), 1).append(' '); // dconvertToAbbr(sb, wtb[date.getMonth() - 1 + 2 + 7]).append(' ');  // MMMsb.append(date.getYear()).append(' ');                            // yyyyCalendarUtils.sprintf0d(sb, date.getHours(), 2).append(':');      // HHCalendarUtils.sprintf0d(sb, date.getMinutes(), 2).append(':');    // mmCalendarUtils.sprintf0d(sb, date.getSeconds(), 2);                // sssb.append(" GMT");                                                // ' GMT'return sb.toString();}@Deprecatedpublic int getTimezoneOffset() {int zoneOffset;if (cdate == null) {TimeZone tz = TimeZone.getDefaultRef();if (tz instanceof ZoneInfo) {zoneOffset = ((ZoneInfo)tz).getOffsets(fastTime, null);} else {zoneOffset = tz.getOffset(fastTime);}} else {normalize();zoneOffset = cdate.getZoneOffset();}return -zoneOffset/60000;  // convert to minutes}private final BaseCalendar.Date getCalendarDate() {if (cdate == null) {BaseCalendar cal = getCalendarSystem(fastTime);cdate = (BaseCalendar.Date) cal.getCalendarDate(fastTime,TimeZone.getDefaultRef());}return cdate;}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;}/*** Save the state of this object to a stream (i.e., serialize it).** @serialData The value returned by <code>getTime()</code>*             is emitted (long).  This represents the offset from*             January 1, 1970, 00:00:00 GMT in milliseconds.*/private void writeObject(ObjectOutputStream s)throws IOException{s.writeLong(getTimeImpl());}/*** Reconstitute this object from a stream (i.e., deserialize it).*/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());}
}