Dates and Times - Beginning Java 8 Fundamentals - page 474

Listing 12-29. Converting a Date to an Instant and Vice Versa

// DateAndInstant.java
package com.jdojo.datetime;

import java.util.Date;
import java.time.Instant;

public class DateAndInstant {
public static void main(String[] args) {
// Get the current date
Date dt = new Date();
System.out.println("Date: " + dt);

// Convert the Date to an Insatnt
Instant in = dt.toInstant();
System.out.println("Instant: " + in);

// Convert the Instant back to a Date
Date dt2 = Date.from(in);
System.out.println("Date: " + dt2);
}
}

Date: Sat Jan 11 14:45:02 CST 2014
Instant: 2014-01-11T20:45:02.265Z
Date: Sat Jan 11 14:45:02 CST 2014

Typically, the legacy code uses GregorianCalendar to store date, time, and datetime. You can convert it to a
ZonedDateTime , which can be converted to any other classes in the new Date-Time API. The Calendar class provides a
toInstant() method to convert its instance to an Instant . The Calendar class is abstract. Typically, you would have
an instance of its concrete subclass class, for example, GregorianCalendar . Therefore, converting an Instant to a
GregorianCalendar would be a two-step process:

Instant to a ZonedDateTime,

• Convert the

from() static method of the GregorianCalendar class to get a GregorianCalendar .
The program in Listing 12-30 shows how to convert a GregorianCalendar to a ZonedDateTime and vice versa.
The program also shows how to get a LocalDate , LocalTime , etc. from a GregorianCalendar . You may get a little
different output because the output depends on the system's default time zone.

• Use the

Listing 12-30. Converting a GregorianCalendar to New Datetime Types and Vice Versa
// GregorianCalendarAndNewDateTime.java
package com.jdojo.datetime;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.OffsetDateTime;