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Java Clock fixed()

By Arvind Rai, May 16, 2019
Java Clock.fixed returns a fixed clock that always gives the same instant. The fixed clock simply returns the specified instant. The main use case of fixed clock is in testing, where the fixed clock ensures tests are not dependent on the current clock.
Find the Clock.fixed declaration from Java doc.
public static Clock fixed(Instant fixedInstant, ZoneId zone) 
We need to pass instant and zone and will return clock with fixed instant. The specified instant will be the fixed instant for the fixed clock obtained by Clock.fixed method.

Clock.fixed Example

We can create a fixed clock using Clock.fixed as following.
Instant instant = Instant.parse("2018-01-08T15:34:42.00Z");
ZoneId zoneId = ZoneId.of("Asia/Calcutta");
Clock clock = Clock.fixed(instant, zoneId); 
The clock object will always give the same instant as specified. Find the example.
FixedClockDemo.java
package com.concretepage;
import java.time.Clock;
import java.time.Instant;
import java.time.ZoneId;
public class FixedClockDemo {
  public static void main(String[] args) {
	Instant instant = Instant.parse("2018-01-08T15:34:42.00Z");
	ZoneId zoneId = ZoneId.of("Asia/Calcutta");
	Clock clock = Clock.fixed(instant, zoneId);

	for (int i = 1; i <= 3; i++) {
	  System.out.println("-----" + i + "-----");
	  System.out.println(clock.instant());
	  try {
		Thread.sleep(2000);
	  } catch (InterruptedException e) {
		e.printStackTrace();
	  }
	}
  }
} 
Output
-----1-----
2018-01-08T15:34:42Z
-----2-----
2018-01-08T15:34:42Z
-----3-----
2018-01-08T15:34:42Z 

Clock.fixed with Offset

We can add or subtract time to fixed clock using its Clock.offset method.
Suppose we have a fixed clock.
Clock clock = Clock.fixed(instant, zoneId); 
We will add 20 minutes to the base fixed clock and will get new instance of fixed clock.
Clock clockPlus = Clock.offset(clock, Duration.ofMinutes(20)); 
Now we will subtract 10 minutes from the base fixed clock and will get new instance of fixed clock.
Clock clockMinus = Clock.offset(clock, Duration.ofMinutes(-10)); 
Find the example.
FixedClockOffset.java
package com.concretepage;
import java.time.Clock;
import java.time.Duration;
import java.time.Instant;
import java.time.ZoneId;
public class FixedClockOffset {
  public static void main(String[] args) {
	Instant instant = Instant.parse("2019-01-08T15:34:42.00Z");
	ZoneId zoneId = ZoneId.systemDefault();

	Clock clock = Clock.fixed(instant, zoneId);
	Clock clockPlus = Clock.offset(clock, Duration.ofMinutes(20));
	Clock clockMinus = Clock.offset(clock, Duration.ofMinutes(-10));

	for (int i = 1; i <= 3; i++) {
	  System.out.println("-----" + i + "-----");
	  System.out.println("Base: " + clock.instant());
	  System.out.println("Plus: " + clockPlus.instant());
	  System.out.println("Minus: " + clockMinus.instant());

	  try {
		Thread.sleep(2000);
	  } catch (InterruptedException e) {
		e.printStackTrace();
	  }
	}
  }
} 
Output
-----1-----
Base: 2019-01-08T15:34:42Z
Plus: 2019-01-08T15:54:42Z
Minus: 2019-01-08T15:24:42Z
-----2-----
Base: 2019-01-08T15:34:42Z
Plus: 2019-01-08T15:54:42Z
Minus: 2019-01-08T15:24:42Z
-----3-----
Base: 2019-01-08T15:34:42Z
Plus: 2019-01-08T15:54:42Z
Minus: 2019-01-08T15:24:42Z 

References

Java Doc: Class Clock
Java Clock
POSTED BY
ARVIND RAI
ARVIND RAI
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