ClockTimeTest.java

package com.example.todo.common.datetime;

import java.time.Clock;
import java.time.ZoneId;
import java.time.ZonedDateTime;

public class ClockTimeTest {

  public static void main(String[] args) {
    Clock utc = Clock.systemUTC();
    System.out.printf("clock: %s\n", utc);
    System.out.printf("zone: %s\n", utc.getZone());
    System.out.printf("ZonedDateTime.now: %s\n", ZonedDateTime.now(utc));
    System.out.printf("clock.instant: %s\n", utc.instant());
    System.out.printf("clock.instant.toEpochMilli: %s\n", utc.instant().toEpochMilli());

    System.out.println();

    Clock tokyo = Clock.system(ZoneId.of("Asia/Tokyo"));
    System.out.printf("clock: %s\n", tokyo);
    System.out.printf("zone: %s\n", tokyo.getZone());
    System.out.printf("ZonedDateTime.now: %s\n", ZonedDateTime.now(tokyo));
    System.out.printf("clock.instant: %s\n", tokyo.instant());
    System.out.printf("clock.instant.toEpochMilli: %s\n", tokyo.instant().toEpochMilli());
  }

}

output.txt

clock: SystemClock[Z]
zone: Z
ZonedDateTime.now: 2018-07-13T09:36:59.612Z
clock.instant: 2018-07-13T09:36:59.616Z
clock.instant.toEpochMilli: 1531474619695

clock: SystemClock[Asia/Tokyo]
zone: Asia/Tokyo
ZonedDateTime.now: 2018-07-13T18:36:59.702+09:00[Asia/Tokyo]
clock.instant: 2018-07-13T09:36:59.703Z
clock.instant.toEpochMilli: 1531474619703