Clock class

By / 22 May 2025 / 2 minutes of reading

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 Clock makes time-related logic more testable and configurable.

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