Java 8 – Date Time API

Java 8 comes with a much improved and much required change in the way date and time is handled.
The classes that represent the date and time concepts are present in the java.time package.

The important classes in this package are:

• java.time.Period: This class represents the date part of the datetime. It represents the date part in terms of days, months and years. for example 1 year, 2 months and 5 days
• java.time.Duration: This class represents the time part of the datetime. It represents the time part in terms of seconds and nanoseconds. for example ’29 seconds’
• java.time.Instant: This represents a particular instant in the timeline. It stores the number of seconds through epoch time and also has another field that stores the nanoseconds
• java.time.LocalDate: This stores the date part of date-time in terms of years-months-days. It does not store the TimeZone. The class is immutable.
• java.time.LocalTime: This class stores the time part of date time without any TimeZone info.
• java.time.LocalDateTime: This class stores the LocalDate and LocalTime but no TimeZone
• java.time.ZonedDateTime: This class stores the LocalDateTime and the TimeZone info as a ZoneOffset object. The class has access to ZoneRules which can be used to convert to local time
• java.time.ZoneOffset:This stores the time zone offset from UTC. The zone rules are stored in ZoneId.
• java.time.OffsetDateTime:This stores the local datetime with the offset. This class does not have information about Zone Rules.

 1 package java8.datetime;
 2 
 3 import java.time.LocalDate;
 4 import java.time.LocalTime;
 5 
 6 /**
 7  * Java 8 – Date Time API
 8  * LocalTime：當前時間
 9  * LocalDate：當前日期
10  */
11 public class LocalTimeDemo3 {
12     public static void main(String[] args) {
13         LocalTime localTime = LocalTime.now();
14         System.out.println("當前時間：" + localTime);
15 
16         LocalDate localDate = LocalDate.now();
17         System.out.println("當前日期：" + localDate);
18     }
19 }

LocalDateTime

 1 package java8.datetime;
 2 
 3 import java.time.DayOfWeek;
 4 import java.time.LocalDateTime;
 5 import java.time.ZoneId;
 6 import java.time.temporal.ChronoField;
 7 
 8 /**
 9  * Java 8 – Date Time API
10  * LocalDateTime
11  * url：http://www.studytrails.com/java/java8/java8_date_and_time/
12  */
13 public class LocalDateTimeDemo2 {
14     public static void main(String[] args) {
15 //        create a LocalDateTime
16         LocalDateTime localDateTime = LocalDateTime.now();
17         System.out.println("新建LocalDateTime對象：" + localDateTime); // prints 2018-02-12T15:08:44.116
18 
19 //        Convert LocalDateTime to datetime in particular zone
20         System.out.println("指定時區：" + localDateTime.atZone(ZoneId.of("America/New_York")));
21 
22 //        Get the day of week from DateTime
23         System.out.println("星期幾：" + DayOfWeek.from(localDateTime)); // prints SUNDAY.
24 
25 //        Get the day of year from DateTime
26         System.out.println("當年第幾天：" + localDateTime.get(ChronoField.DAY_OF_YEAR)); // prints 43
27 //        The other fields that can be returned are MINUTE_OF_HOUR, MINUTE_OF_DAY, HOUR_OF_AMPM,
28 //        HOUR_OF_DAY, AMPM_OF_DAY, DAY_OF_WEEK, DAY_OF_MONTH, DAY_OF_YEAR, MONTH_OF_YEAR,
29 //        YEAR, OFFSET_SECONDS (offset from UTC).
30 
31 //       獲得當前日期
32         System.out.println("當前日期：" + localDateTime.toLocalDate());
33         // prints 2014-09-29
34 
35         // 獲取當前時間
36         System.out.println("當前時間：" + localDateTime.toLocalTime());
37         // prints 22:26:30.146
38 
39 //        Create a LocalDateTime from year, month, day, hour, min
40         System.out.println("實例化LocalDateTime by Int：" + LocalDateTime.of(2014, 10, 1, 10, 0));
41         // prints 2014-10-01T10:00
42 
43 //        Create LocalDateTime by parsing a string
44         LocalDateTime parsedLocalDateTime = LocalDateTime.parse("2014-01-01T11:00");
45         System.out.println("實例化LocalDateTime by String：" + parsedLocalDateTime);
46 
47         System.out.println("當前小時點：" + localDateTime.getHour());
48 
49 
50     }
51 }

Instant

 1 package java8.datetime;
 2 
 3 import java.time.Instant;
 4 import java.time.temporal.ChronoUnit;
 5 
 6 /**
 7  * Java 8 – Date Time API
 8  * Instant
 9  * url：http://www.studytrails.com/java/java8/java8_date_and_time/
10  */
11 public class InstantDemo1 {
12     public static void main(String[] args) {
13         //Creating a local date
14         Instant now = Instant.now();
15         //2018-02-12T06:29:01.493Z
16         System.out.println("當前時間：" + now);
17 
18 //      The epoch seconds is the number of seconds since 1970-01-01T00:00:00Z
19         System.out.println("當前秒數：" + now.getEpochSecond());
20 
21 //      調整時間
22 //      the plus function allows adding time intervals.
23 //      The time intervals can be NANOS, MICROS, MILLIS, SECONDS, MINUTES, HOURS, HALF_DAYS, DAYS
24         Instant tomorrow = now.plus(2, ChronoUnit.DAYS);
25         System.out.println("明天時間：" + tomorrow);
26 //        The minus function allows subtracting time from an instant.
27         Instant yesterday = now.minus(1, ChronoUnit.DAYS);
28         System.out.println("昨天時間：" + yesterday);
29 
30 //      The compare function can be used to compare two dates.
31 //      It returns -1 if the date that is passed is after , 1 if it is before
32         System.out.println("今天和明天比較：" + now.compareTo(tomorrow));// prints -1
33 
34 //        check if one instant is after another
35         System.out.println("今天是否在昨天後面：" + now.isAfter(yesterday));// prints true
36 
37     }
38 }

Java之Date Time API (Java 8 新特性)