Clock systemUTC() Method in Java with Examples - GeeksforGeeks

10 Dec, 2018
java.time.Clock.systemUTC() method is a static method of Clock class which returns a clock that returns the current instant of the clock using the best available system clock where Zone of the returned clock is UTC time-zone.
When the current instant is needed without the date or time, then use systemUTC() method in place of systemDefaultZone().
When converting instant to date and time, then the converter uses UTC time-zone as Zone for conversion. This clock is based on the best available system clock. This method can use System.currentTimeMillis(), or other higher resolution clock for its implementation if the clock is available to use.
Returned clock from this method is immutable, thread-safe and Serializable.
Syntax:
public static Clock systemUTC()
Return Value: This method returns a clock that uses the best available system clock in the UTC time-zone
Example:
Code:
//Clock with default zone
Clock clock=Clock.systemUTC();
System.out.println(clock.instant());

Output:: 
2018-08-21T20:38:10.772Z

Explanation:: 
when you call systemUTC() for Clock then the systemUTC()
method will return a Class Object whose Zone is UTC time zone.

Below programs illustrates systemUTC() method of java.time.Clock class:
Program 1: When Clock is created with systemUTC().
This method makes clock zone to UTC Zone.Below program print date and time of clock in ZonedDateTime format.
// Java program to demonstrate// systemUTC() method of Clock class  import java.time.*;  // create classpublic class systemUTCMethodDemo {      // Main method    public static void main(String[] args)    {          // create Clock with systemUTC() method        Clock clock = Clock.systemUTC();          // get instant of class        Instant instant = clock.instant();          // get ZonedDateTime object from instantObj        // to get date time        ZonedDateTime time = instant.atZone(clock.getZone());          // print details of ZonedDateTime        System.out.println("ZonedDateTime of class with UTC"                           + " Time Zone is "                           + time.toString());    }}
ZonedDateTime of class with UTC Time Zone is 2018-08-22T11:41:15.554Z

Program 2: Print the zoneId using getZone() for clock created by systemUTC().
// Java program to demonstrate// systemUTC() method of Clock class  import java.time.*;  // create classpublic class systemUTCMethodDemo {      // Main method    public static void main(String[] args)    {          // create Clock with systemUTC() method        Clock clock = Clock.systemUTC();          // get ZoneId of Clock        ZoneId zone = clock.getZone();          // print details of ZoneId of new Clock        System.out.println("ZoneID of class is " + zone);    }}
ZoneID of class is Z

Reference:https://docs.oracle.com/javase/8/docs/api/java/time/Clock.html#systemUTC–
java-basics
Java-Clock
Java-Functions
Java-time package
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