The Clock class is part of the java.time package and provides an abstraction to access the current instant, date, and time using a time-zone.This abstract an class.
It allows applications to:
- Get the current time in a consistent and testable way.
- Work with different time zones or offsets.
- Be used to inject clocks for unit testing.
Common used Methods
Simple Program
import java.time.Clock;
import java.time.Instant;
import java.time.ZoneId;
public class ClockExample {
public static void main(String[] args) {
Clock utcClock = Clock.systemUTC();
Clock defaultClock = Clock.systemDefaultZone();
System.out.println("UTC Time: " + Instant.now(utcClock));
System.out.println("System Default Zone: " + defaultClock.getZone());
System.out.println("Local Time: " + Instant.now(defaultClock));
}
}Problem Statement
LotusJavaPrince and Mahesh are developing a logging system that uses:
- A system clock for production logs.
- A fixed clock for testing.
- An offset clock for simulating server lag.
The goal is to demonstrate consistent, testable, and simulated time using the Clock class.
import java.time.Clock;
import java.time.Duration;
import java.time.Instant;
import java.time.ZoneId;
public class LoggingSystem {
public static void main(String[] args) {
System.out.println("Logging System - Created by LotusJavaPrince and Mahesh");
// System clock (real-time)
Clock systemClock = Clock.systemDefaultZone();
// Fixed clock (mocked time)
Clock fixedClock = Clock.fixed(Instant.parse("2025-01-01T00:00:00Z"), ZoneId.of("UTC"));
// Offset clock (simulated 5-minute delay)
Clock offsetClock = Clock.offset(systemClock, Duration.ofMinutes(-5));
// Displaying all clocks
System.out.println("System Time: " + Instant.now(systemClock));
System.out.println("Fixed Time: " + Instant.now(fixedClock));
System.out.println("Offset Time (simulated delay): " + Instant.now(offsetClock));
}
}
/*
Logging System - Created by LotusJavaPrince and Mahesh
System Time: 2025-05-22T10:30:00.000Z
Fixed Time: 2025-01-01T00:00:00Z
Offset Time (simulated delay): 2025-05-22T10:25:00.000Z
&/The Clock class is an essential utility in Java’s date-time API that decouples time retrieval from system time.
- Useful for testing, simulation, and time zone handling.
- Provides precise control over how time is handled in applications, like LotusJavaPrince and Mahesh’s logging system.
- When writing enterprise or production software, using
Clockmakes time-related logic more testable and configurable.