Date date = new Date(2012,1,1);
System.out.println(date);

Calendar calendar = Calendar.getInstance();
calendar.set(2013, 8, 2);

calendar.set(2013, Calendar.AUGUST, 2);

public static void main(String[] args) {
  Calendar birth = Calendar.getInstance();
  birth.set(1975, Calendar.MAY, 26);
  Calendar now = Calendar.getInstance();
  System.out.println(daysBetween(birth, now));
  System.out.println(daysBetween(birth, now)); // 显示 0？
 } 
public static long daysBetween(Calendar begin, Calendar end) {
  long daysBetween = 0;
  while(begin.before(end)) {
    begin.add(Calendar.DAY_OF_MONTH, 1);
    daysBetween++;
  }
  return daysBetween;
}

public static long daysBetween(Calendar begin, Calendar end) {
  Calendar calendar = (Calendar) begin.clone(); // 复制
  long daysBetween = 0;
  while(calendar.before(end)) {
    calendar.add(Calendar.DAY_OF_MONTH, 1);
    daysBetween++;
  }
  return daysBetween;
}

public class TimeIntroduction {
  public static void testClock() throws InterruptedException {
    //时钟提供给我们用于访问某个特定 时区的 瞬时时间、日期 和 时间的。 
    Clock c1 = Clock.systemUTC(); //系统默认UTC时钟（当前瞬时时间 System.currentTimeMillis()） 
    System.out.println(c1.millis()); //每次调用将返回当前瞬时时间（UTC） 
    Clock c2 = Clock.systemDefaultZone(); //系统默认时区时钟（当前瞬时时间） 
    Clock c31 = Clock.system(ZoneId.of("Europe/Paris")); //巴黎时区 
    System.out.println(c31.millis()); //每次调用将返回当前瞬时时间（UTC） 
    Clock c32 = Clock.system(ZoneId.of("Asia/Shanghai"));//上海时区 
    System.out.println(c32.millis());//每次调用将返回当前瞬时时间（UTC） 
    Clock c4 = Clock.fixed(Instant.now(), ZoneId.of("Asia/Shanghai"));//固定上海时区时钟 
    System.out.println(c4.millis());
    Thread.sleep(1000);
    System.out.println(c4.millis()); //不变 即时钟时钟在那一个点不动 
    Clock c5 = Clock.offset(c1, Duration.ofSeconds(2)); //相对于系统默认时钟两秒的时钟 
    System.out.println(c1.millis());
    System.out.println(c5.millis());
  }
  public static void testInstant() {
    //瞬时时间 相当于以前的System.currentTimeMillis() 
    Instant instant1 = Instant.now();
    System.out.println(instant1.getEpochSecond());//精确到秒 得到相对于1970-01-01 00:00:00 UTC的一个时间 
    System.out.println(instant1.toEpochMilli()); //精确到毫秒 
    Clock clock1 = Clock.systemUTC(); //获取系统UTC默认时钟 
    Instant instant2 = Instant.now(clock1);//得到时钟的瞬时时间 
    System.out.println(instant2.toEpochMilli());
    Clock clock2 = Clock.fixed(instant1, ZoneId.systemDefault()); //固定瞬时时间时钟 
    Instant instant3 = Instant.now(clock2);//得到时钟的瞬时时间 
    System.out.println(instant3.toEpochMilli());//equals instant1 
  }
  public static void testLocalDateTime() {
    //使用默认时区时钟瞬时时间创建 Clock.systemDefaultZone() -->即相对于 ZoneId.systemDefault()默认时区 
    LocalDateTime now = LocalDateTime.now();
    System.out.println(now);
//自定义时区 
    LocalDateTime now2 = LocalDateTime.now(ZoneId.of("Europe/Paris"));
    System.out.println(now2);//会以相应的时区显示日期 
//自定义时钟 
    Clock clock = Clock.system(ZoneId.of("Asia/Dhaka"));
    LocalDateTime now3 = LocalDateTime.now(clock);
    System.out.println(now3);//会以相应的时区显示日期 
//不需要写什么相对时间 如java.util.Date 年是相对于1900 月是从0开始 
//2013-12-31 23:59 
    LocalDateTime d1 = LocalDateTime.of(2013, 12, 31, 23, 59);
//年月日 时分秒 纳秒 
    LocalDateTime d2 = LocalDateTime.of(2013, 12, 31, 23, 59, 59, 11);
//使用瞬时时间 + 时区 
    Instant instant = Instant.now();
    LocalDateTime d3 = LocalDateTime.ofInstant(Instant.now(), ZoneId.systemDefault());
    System.out.println(d3);
//解析String--->LocalDateTime 
    LocalDateTime d4 = LocalDateTime.parse("2013-12-31T23:59");
    System.out.println(d4);
    LocalDateTime d5 = LocalDateTime.parse("2013-12-31T23:59:59.999");//999毫秒 等价于999000000纳秒 
    System.out.println(d5);
//使用DateTimeFormatter API 解析 和 格式化 
    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
    LocalDateTime d6 = LocalDateTime.parse("2013/12/31 23:59:59", formatter);
    System.out.println(formatter.format(d6));
//时间获取 
    System.out.println(d6.getYear());
    System.out.println(d6.getMonth());
    System.out.println(d6.getDayOfYear());
    System.out.println(d6.getDayOfMonth());
    System.out.println(d6.getDayOfWeek());
    System.out.println(d6.getHour());
    System.out.println(d6.getMinute());
    System.out.println(d6.getSecond());
    System.out.println(d6.getNano());
//时间增减 
    LocalDateTime d7 = d6.minusDays(1);
    LocalDateTime d8 = d7.plus(1, IsoFields.QUARTER_YEARS);
//LocalDate 即年月日 无时分秒 
//LocalTime即时分秒 无年月日 
//API和LocalDateTime类似就不演示了 
  }
  public static void testZonedDateTime() {
    //即带有时区的date-time 存储纳秒、时区和时差（避免与本地date-time歧义）。 
//API和LocalDateTime类似，只是多了时差(如2013-12-20T10:35:50.711+08:00[Asia/Shanghai]) 
    ZonedDateTime now = ZonedDateTime.now();
    System.out.println(now);
    ZonedDateTime now2 = ZonedDateTime.now(ZoneId.of("Europe/Paris"));
    System.out.println(now2);
//其他的用法也是类似的 就不介绍了 
    ZonedDateTime z1 = ZonedDateTime.parse("2013-12-31T23:59:59Z[Europe/Paris]");
    System.out.println(z1);
  }
  public static void testDuration() {
    //表示两个瞬时时间的时间段 
    Duration d1 = Duration.between(Instant.ofEpochMilli(System.currentTimeMillis() - 12323123), Instant.now());
//得到相应的时差 
    System.out.println(d1.toDays());
    System.out.println(d1.toHours());
    System.out.println(d1.toMinutes());
    System.out.println(d1.toMillis());
    System.out.println(d1.toNanos());
//1天时差 类似的还有如ofHours() 
    Duration d2 = Duration.ofDays(1);
    System.out.println(d2.toDays());
  }
  public static void testChronology() {
    //提供对java.util.Calendar的替换，提供对年历系统的支持 
    Chronology c = HijrahChronology.INSTANCE;
    ChronoLocalDateTime d = c.localDateTime(LocalDateTime.now());
    System.out.println(d);
  }
  /**
   * 新旧日期转换
   */
  public static void testNewOldDateConversion(){
    Instant instant=new Date().toInstant();
    Date date=Date.from(instant);
    System.out.println(instant);
    System.out.println(date);
  }
  public static void main(String[] args) throws InterruptedException {
    testClock();
    testInstant();
    testLocalDateTime();
    testZonedDateTime();
    testDuration();
    testChronology();
    testNewOldDateConversion();
  }
}