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Introduction to commonly used time APIs and usage methods in Java

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2023-05-07 09:04:13994browse

1. The Clock class can be used to access the current date and time. Clock can get the current time zone instead of System.currenttimeMillis().

Clock clock = Clock.systemDefaultZone();long millis = clock.millis();
 
Instant instant = clock.instant();
Date legacyDate = Date.from(instant);   // legacy java.util.Date

2. Time is represented by zoneId, and zoneId can be accessed through the static factory.

System.out.println(ZoneId.getAvailableZoneIds());// prints all available timezone ids
 
ZoneId zone1 = ZoneId.of("Europe/Berlin");
ZoneId zone2 = ZoneId.of("Brazil/East");
System.out.println(zone1.getRules());
System.out.println(zone2.getRules());
 
// ZoneRules[currentStandardOffset=+01:00]
// ZoneRules[currentStandardOffset=-03:00]

3. LocalTime means there is no time zone, such as 10pm or 17:30:15.

LocalTime now1 = LocalTime.now(zone1);
LocalTime now2 = LocalTime.now(zone2);
 
System.out.println(now1.isBefore(now2));  // false
 
long hoursBetween = ChronoUnit.HOURS.between(now1, now2);
long minutesBetween = ChronoUnit.MINUTES.between(now1, now2);
 
System.out.println(hoursBetween);       // -3
System.out.println(minutesBetween);     // -239

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