Java - Interoperability with Legacy Date time Classes

Introduction

Java provides interoperability between the legacy classes and the new Date-Time API.

New methods have been added to the legacy classes to convert their objects to the new Date-Time classes and vice versa.

The following table contains the list of legacy datetime classes and their new Date-Time counterparts.

All legacy classes, except the Calendar class, provides two-way conversion.

The toXxx() methods are instance methods which return an object of the new datetime class.

The other methods are static methods, which accept an object of the new datetime class and return an object of the legacy class.

from() method in the java.util.Date class is a static method, which takes an Instant argument and returns a java.util.Date.

toInstant() method is an instance method and converts a java.util.Date into an Instant.

Legacy Class
New Methods in Legacy Class
Equivalent New Datetime Class
java.util.Date
from(), toInstant()
Instant
Calendar
toInstant()
None
GregorianCalendar
from(), toZonedDateTime()
ZonedDateTime
TimeZone
getTimeZone(), toZoneId()
ZoneId
java.sql.Date
valueOf(), toLocalDate()
LocalDate
Time
valueOf(), toLocalTime()
LocalTime
Timestamp
from(), toInstant()
Instant
valueOf(), toLocalDateTime()
LocalDateTime
FileTime
from(), toInstant()
Instant

The following code shows how to convert a Date to an Instant and vice versa.

Demo

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

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

    // Convert the Date to an Instant
    Instant in = dt.toInstant();/*  w  w  w . j  a  va  2  s. c o m*/
    System.out.println("Instant: " + in);

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

Result

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