Java 8 Clock millis() Method with Examples

Java Clock class is part of Date Time API, java.time.Clock, of Java. The Java Date Time API was added from Java version 8.
The millis() method of Clock class returns the current instant of the clock in milliseconds. A millisecond instant is measured from 1970-01-01T00:00Z (UTC) to the current time. This method does the same work as System.currentTimeMillis() method. If the creation of an object is unacceptable, then this method is used to allow the use of java.time.Clock in high-performance use cases.
Syntax:

public long millis()

Return Value: This method returns the current instant of the clock in milliseconds.
Exception: This method throws DateTimeException if the instant cannot be obtained from Clock.
Example:: 

Code:
Clock clock = Clock.systemDefaultZone();
long milliSeconds=clock.millis();
System.out.println(milliSeconds);

Output:: 
1534749202051

Explanation:: 
when millis() is called, then it returns a current instant
of Class Object in milliseconds. 

Below programs illustrates millis() method of java.time.Clock class:
Program 1: Using millis() with Clock object created with systemDefaultZone

Java

// Java program to demonstrate millis()
// method of Clock class

import java.time.*;

// create class
public class millisMethodDemo {

    // Main method
    public static void main(String[] args)
    {

        // create Clock Object
        Clock clock = Clock.systemDefaultZone();

        // get Instant Object of Clock object
        // in milliseconds using millis() method
        long milliseconds = clock.millis();

        // print details of milliseconds variable
        System.out.println("Instant for class name "
                           + clock + " in milliseconds is "
                           + milliseconds);
    }
}

Output

Instant for class name SystemClock[Etc/UTC] in milliseconds is 1623838188802

Program 2: Using millis with Clock object created with Zone “Europe/Paris”

Java

// Java program to demonstrate millis()
// method of Clock class

import java.time.*;

// create class
public class millisMethodDemo {

    // Main method
    public static void main(String[] args)
    {

        // create a Zone Id for Europe/Paris
        ZoneId zoneId = ZoneId.of("Europe/Paris");

        // create Clock Object by passing zoneID
        Clock clock = Clock.system(zoneId);

        // get Instant Object of Clock object
        // in milliseconds using millis() method
        long milliseconds = clock.millis();

        // print details of milliseconds variable
        System.out.println("Instant for clock class"
                           + " in milliseconds is " + milliseconds);
    }
}

Output

Instant for clock class in milliseconds is 1623837795533

Reference: https://docs.oracle.com/javase/8/docs/api/java/time/Clock.html#millis–