JDK Tutorials - Herong's Tutorial Examples

∟Java Date-Time API

∟java.time.Instant Usage Examples

This section provides a tutorial example on how to use the java.time.Instant class to capture the current time, and to retrieve Epoch-Second value and Nanosecond-of-Second value. The system clock on Windows only supports millisecond resolution.

To test out the java.time.Instant class, I wrote the following example program, InstantTest.java: 

/* InstantTest.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.time.Instant;
class InstantTest {
   public static void main(String[] a) {
      java.io.PrintStream out = System.out;
      // Instant now = new Instant(); // constructor is not supported

      Instant now = Instant.now();
      out.println("Current moment of time:");
      out.println("toString() = " + now.toString());
      out.println("getEpochSecond() = " + now.getEpochSecond());
      out.println("getNano() = " + now.getNano());
      out.println("get(MILLI_OF_SECOND) = " + now.get(
         java.time.temporal.ChronoField.MILLI_OF_SECOND));

      Instant later = now.plus(1,java.time.temporal.ChronoUnit.HOURS);
      out.println();
      out.println("1 hour later:");
      out.println("toString() = " + later.toString());
      out.println("getEpochSecond() = " + later.getEpochSecond());
      out.println("getNano() = " + later.getNano());

      Instant epoch = Instant.parse("1970-01-01T00:00:00.000Z");
      out.println();
      out.println("Epoch point of time:");
      out.println("toString() = " + epoch.toString());
      out.println("getEpochSecond() = " + epoch.getEpochSecond());
      out.println("getNano() = " + epoch.getNano());

      Instant dob = Instant.parse("1879-03-17T00:00:00.000Z");
      out.println();
      out.println("Einstein birth date:");
      out.println("toString() = " + dob.toString());
      out.println("getEpochSecond() = " + dob.getEpochSecond());
      out.println("getNano() = " + dob.getNano());
   }
}

When running InstantTest.java with JDK 9, or higher, I got the following output: 

herong> java InstantTest.java

Current moment of time:
toString() = 2019-04-01T17:48:21.397800100Z
getEpochSecond() = 1531936101
getNano() = 397800100
get(MILLI_OF_SECOND) = 397

1 hour later:
toString() = 2019-04-01T18:48:21.397800100Z
getEpochSecond() = 1531939701
getNano() = 397800100

Epoch point of time:
toString() = 1970-01-01T00:00:00Z
getEpochSecond() = 0
getNano() = 0

Einstein birth date:
toString() = 1879-03-17T00:00:00Z
getEpochSecond() = -2865196800
getNano() = 0

Interesting notes from the output:

When running InstantTest.java with JDK 1.8, I got the following output: 

herong> \progra~1\java\jdk1.8.0\bin\javac InstantTest.java

herong> \progra~1\java\jdk1.8.0\bin\java InstantTest
Current moment of time:
toString() = 2014-04-01T05:48:41.750Z
getEpochSecond() = 1396331321
getNano() = 750000000
get(MILLI_OF_SECOND) = 750

1 hour later:
toString() = 2014-04-01T06:48:41.750Z
getEpochSecond() = 1396327721
getNano() = 750000000

Epoch point of time:
toString() = 1970-01-01T00:00:00Z
getEpochSecond() = 0
getNano() = 0

Einstein birth date:
toString() = 1879-03-17T00:00:00Z
getEpochSecond() = -2865196800
getNano() = 0

Interesting notes from the output:

Table of Contents

 About This JDK Tutorial Book

 JDK (Java Development Kit)

►Java Date-Time API

 What Is Date-Time API

 java.time.Instant - Representing a Moment of Time

►java.time.Instant Usage Examples

 java.time.Instant - get(INSTANT_SECONDS) Error

 Converting java.util.Date to java.time.Instant

 java.time.ZonedDateTime - Calendar and Timezone

 java.time.ZonedDateTime Usage Examples

 Converting java.util.GregorianCalendar to java.time.ZonedDateTime

 java.time.OffsetDateTime - Calendar and UTC Offset

 java.time.OffsetDateTime Usage Examples

 java.time.LocalDateTime - Local Date and time without Timezone

 Partial Date and Time Objects and Classes

 java.time.format.DateTimeFormatter - Date-Time Strings

 java.time.Duration - Time Durations

 java.time.Duration Usage Examples

 java.time.Period - Periods in Days and Months

 java.time.Period Usage Examples

 Date, Time and Calendar Classes

 Date and Time Object and String Conversion

 Number Object and Numeric String Conversion

 Locales, Localization Methods and Resource Bundles

 Calling and Importing Classes Defined in Unnamed Packages

 HashSet, Vector, HashMap and Collection Classes

 Character Set Encoding Classes and Methods

 Character Set Encoding Maps

 Encoding Conversion Programs for Encoded Text Files

 Java Logging

 Socket Network Communication

 Datagram Network Communication

 DOM (Document Object Model) - API for XML Files

 SAX (Simple API for XML)

 DTD (Document Type Definition) - XML Validation

 XSD (XML Schema Definition) - XML Validation

 XSL (Extensible Stylesheet Language)

 Message Digest Algorithm Implementations in JDK

 Private key and Public Key Pair Generation

 PKCS#8/X.509 Private/Public Encoding Standards

 Digital Signature Algorithm and Sample Program

 "keytool" Commands and "keystore" Files

 KeyStore and Certificate Classes

 Secret Key Generation and Management

 Cipher - Encryption and Decryption

 The SSL (Secure Socket Layer) Protocol

 SSL Socket Communication Testing Programs

 SSL Client Authentication

 HTTPS (Hypertext Transfer Protocol Secure)

 Outdated Tutorials

 References

 Full Version in PDF/EPUB