How to find the difference between two LocalDateTime objects?

By I Wayan Saryada in Java Date Time API 0 Comment

In the previous post, How do I find the difference between two times?, we get the difference between two LocalTime objects in seconds measurement. In this example we will get the difference between two LocalDateTime objects and get the difference between these objects in years, months, days, hours, minutes, seconds and milliseconds.

package org.kodejava.datetime;

import java.time.LocalDateTime;
import java.time.Month;
import java.time.temporal.ChronoUnit;

public class LocalDateTimeDiff {
    public static void main(String[] args) {
        LocalDateTime from = LocalDateTime.of(2021, Month.JANUARY, 10, 10, 0, 30);
        LocalDateTime to = LocalDateTime.now();

        LocalDateTime fromTemp = LocalDateTime.from(from);
        long years = fromTemp.until(to, ChronoUnit.YEARS);
        fromTemp = fromTemp.plusYears(years);

        long months = fromTemp.until(to, ChronoUnit.MONTHS);
        fromTemp = fromTemp.plusMonths(months);

        long days = fromTemp.until(to, ChronoUnit.DAYS);
        fromTemp = fromTemp.plusDays(days);

        long hours = fromTemp.until(to, ChronoUnit.HOURS);
        fromTemp = fromTemp.plusHours(hours);

        long minutes = fromTemp.until(to, ChronoUnit.MINUTES);
        fromTemp = fromTemp.plusMinutes(minutes);

        long seconds = fromTemp.until(to, ChronoUnit.SECONDS);
        fromTemp = fromTemp.plusSeconds(seconds);

        long millis = fromTemp.until(to, ChronoUnit.MILLIS);

        System.out.println("From = " + from);
        System.out.println("To   = " + to);
        System.out.printf("The difference is %s years, %s months, %s days, " +
                        "%s hours, %s minutes, %s seconds, %s millis",
                years, months, days, hours, minutes, seconds, millis);
    }
}

The result of the code snippet above when executed is:

From = 2021-01-10T10:00:30
To   = 2021-11-17T15:07:37.913247900
The difference is 0 years, 10 months, 7 days, 5 hours, 7 minutes, 7 seconds, 913 millis

How do I find the difference between two times?

By I Wayan Saryada in Java Date Time API 0 Comment

The following code snippet show you how to find the difference between two time objects represented by LocalTime class. To get the difference between two LocalTime objects we can use the Duration.between() method. This method returns a Duration object, to get the difference in seconds we call the getSeconds() method.

Here a code snippet to demonstrate it.

package org.kodejava.datetime;

import java.time.*;

public class TimeDifference {
    public static void main(String[] args) {
        LocalTime start = LocalTime.now();
        LocalTime end = LocalTime.of(16, 59, 55);
        Duration duration = Duration.between(start, end);

        System.out.printf("Seconds between %s and %s is: %s seconds.%n",
                start, end, duration.getSeconds());

        diffLocalDateTime();
        diffInstant();
    }

    /**
     * Difference between two LocalDateTime objects.
     */
    public static void diffLocalDateTime() {
        LocalDateTime dt1 = LocalDateTime.now();
        LocalDateTime dt2 = LocalDateTime.now(ZoneId.of("GMT+0"));
        Duration duration = Duration.between(dt1, dt2);
        System.out.printf("Duration = %s seconds.%n", duration.getSeconds());
    }

    /**
     * Difference between two Instant objects.
     */
    public static void diffInstant() {
        Instant instant1 = Instant.now();
        Instant instant2 = Instant.EPOCH;
        Duration duration = Duration.between(instant1, instant2);
        System.out.printf("Duration = %s seconds.%n", duration.getSeconds());
    }
}

Using the Duration.between() we can also get the difference between two LocalDateTime objects and two Instant object as seen in the diffLocalDateTime() method and diffInstant method in the code snippet above.

The result of the code snippet:

Seconds between 15:05:35.401317900 and 16:59:55 is: 6859 seconds.
Duration = -28800 seconds.
Duration = -1637132736 seconds.

How do I convert between old Date and Calendar object with the new Java 8 Date Time?

By I Wayan Saryada in Java 8, Java Date Time API 0 Comment

In this example we will learn how to convert the old java.util.Date and java.util.Calendar objects to the new Date Time introduced in Java 8. The first method in the code snippet below dateToNewDate() show conversion of java.util.Date while the calendarToNewDate() show the conversion of java.util.Calendar.

The java.util.Date and java.util.Calendar provide a toInstant() method to convert the objects to the new Date Time API class of the java.time.Instant. To convert the old date into the Java 8 LocalDate, LocalTime and LocalDateTime we first can create an instance of ZonedDateTime using the atZone() method of the Instant class.

ZonedDateTime zonedDateTime = instant.atZone(ZoneId.systemDefault());

From an instance of ZonedDateTime class we can call the toLocalDate(), toLocalTime() and toLocalDateTime() to get instance of LocalDate, LocalTime and LocalDateTime.

To convert back from the new Java 8 date to the old java.util.Date we can use the Date.from() static factory method and passing and instance of java.time.Instant that we can obtain by calling the following code.

Instant instant1 = dateTime.atZone(ZoneId.systemDefault()).toInstant();
Date now1 = Date.from(instant1);

Here are the complete code snippet to convert java.util.Date to the new Java 8 Date Time.

private static void dateToNewDate() {
    Date now = new Date();
    Instant instant = now.toInstant();

    ZonedDateTime zonedDateTime = instant.atZone(ZoneId.systemDefault());

    LocalDate date = zonedDateTime.toLocalDate();
    LocalTime time = zonedDateTime.toLocalTime();
    LocalDateTime dateTime = zonedDateTime.toLocalDateTime();

    Instant instant1 = dateTime.atZone(ZoneId.systemDefault()).toInstant();
    Date now1 = Date.from(instant1);

    System.out.println("java.util.Date          = " + now);
    System.out.println("java.time.LocalDate     = " + date);
    System.out.println("java.time.LocalTime     = " + time);
    System.out.println("java.time.LocalDateTime = " + dateTime);
    System.out.println("java.util.Date          = " + now1);
    System.out.println();
}

The steps for converting from the java.util.Calendar to the new Java 8 date can be seen in the code snippet below. As with java.util.Date the Calendar class provide toInstant() method to convert the calendar to java.time.Instant object.

Using the LocalDateTime.ofInstant() method we can create a LocalDateTime object from the instant object. By having the LocalDateTime object we can then get an instance of LocalDate and LocalTime by calling the toLocalDate() and toLocalTime() method.

Finally, to convert back to java.util.Calendar we can use the GregorianCalendar.from() static factory method which require an instance of ZonedDateTime to be passed as a parameter. To get an instance of ZonedDateTime we can call LocalDateTime.atZone() method. You can see the complete code in the code snippet below.

private static void calendarToNewDate() {
    Calendar now = Calendar.getInstance();

    LocalDateTime dateTime = LocalDateTime.ofInstant(now.toInstant(),
            ZoneId.systemDefault());

    LocalDate date = dateTime.toLocalDate();
    LocalTime time = dateTime.toLocalTime();

    ZonedDateTime zonedDateTime = dateTime.atZone(ZoneId.systemDefault());
    Calendar now1 = GregorianCalendar.from(zonedDateTime);

    System.out.println("java.util.Calendar      = " + now);
    System.out.println("java.time.LocalDateTime = " + dateTime);
    System.out.println("java.time.LocalDate     = " + date);
    System.out.println("java.time.LocalTime     = " + time);
    System.out.println("java.util.Calendar      = " + now1);
}

Below is the main Java class to run the code snippet. You must place the above methods inside this class to run the code snippet.

package org.kodejava.datetime;

import java.time.*;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

public class LegacyDateCalendarToNewDateExample {
    public static void main(String[] args) {
        dateToNewDate();
        calendarToNewDate();
    }
}

Here are the result of the code snippet above. The first group is conversion the java.util.Date to the new Date Time API. The second group is conversion from the java.util.Calendar to the new Date Time API.

java.util.Date          = Tue Nov 16 08:44:51 CST 2021
java.time.LocalDate     = 2021-11-16
java.time.LocalTime     = 08:44:51.031
java.time.LocalDateTime = 2021-11-16T08:44:51.031
java.util.Date          = Tue Nov 16 08:44:51 CST 2021

java.util.Calendar      = java.util.GregorianCalendar[time=1637023491089,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=31,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2021,MONTH=10,WEEK_OF_YEAR=47,WEEK_OF_MONTH=3,DAY_OF_MONTH=16,DAY_OF_YEAR=320,DAY_OF_WEEK=3,DAY_OF_WEEK_IN_MONTH=3,AM_PM=0,HOUR=8,HOUR_OF_DAY=8,MINUTE=44,SECOND=51,MILLISECOND=89,ZONE_OFFSET=28800000,DST_OFFSET=0]
java.time.LocalDateTime = 2021-11-16T08:44:51.089
java.time.LocalDate     = 2021-11-16
java.time.LocalTime     = 08:44:51.089
java.util.Calendar      = java.util.GregorianCalendar[time=1637023491089,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=31,lastRule=null],firstDayOfWeek=2,minimalDaysInFirstWeek=4,ERA=1,YEAR=2021,MONTH=10,WEEK_OF_YEAR=46,WEEK_OF_MONTH=3,DAY_OF_MONTH=16,DAY_OF_YEAR=320,DAY_OF_WEEK=3,DAY_OF_WEEK_IN_MONTH=3,AM_PM=0,HOUR=8,HOUR_OF_DAY=8,MINUTE=44,SECOND=51,MILLISECOND=89,ZONE_OFFSET=28800000,DST_OFFSET=0]

How do I get the date of the first particular day after a specific date?

By I Wayan Saryada in Java 8, Java Date Time API 0 Comment

In this example we will learn how to get the date of the first particular day that fall after a specific date. In the code snippet below we will find the first Friday that fall after the new year of 2021. First let’s create a LocalDate object that represent the new year of 2021. We can use LocalDate.of() factory method to create the date object.

To get the first occurrence of a specific day-of-week from a date we create a TemporalAdjuster using the TemporalAdjusters.next() method and pass the day-of-week, in this case we pass DayOfWeek.FRIDAY.

After that we create another LocalDate that will hold the next Friday date. The get the date for the next Friday we call newYear.with() method and pass the TemporalAdjuster that we have created earlier.

Now, let’s try the code snippet below.

package org.kodejava.datetime;

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.Month;
import java.time.temporal.TemporalAdjuster;
import java.time.temporal.TemporalAdjusters;

public class GetFirstDayAfterDate {
    public static void main(String[] args) {
        // Obtains the current date.
        LocalDate newYear = LocalDate.of(2021, Month.JANUARY, 1);
        System.out.println("New Year = " + newYear);

        // Gets the next Friday.
        TemporalAdjuster nextFriday = TemporalAdjusters.next(DayOfWeek.FRIDAY);
        LocalDate nextFridayDate = newYear.with(nextFriday);
        System.out.printf("The first Friday after the new year of %s is %s%n",
                newYear, nextFridayDate);
    }
}

The code snippet will print out the following result:

New Year = 2021-01-01
The first Friday after the new year of 2021-01-01 is 2021-01-08

How do I add or subtract date in Java 8?

By I Wayan Saryada in Java Date Time API 0 Comment

The new Java 8 java.time.LocalDate class provide a plus() and minus() methods to add or subtract an amount of period to or from the LocalDate object.

The period is represented using the java.time.Period class. To create an instance of Period we can use the of(), ofDays(), ofWeeks(), ofMonths() and ofYears() methods.

Let’s see an example using the plus() and minus() method of LocalDate class to add and subtract in the code snippet below:

package org.kodejava.datetime;

import java.time.LocalDate;
import java.time.Period;

public class DateAddSubtract {
    public static void main(String[] args) {
        // Create periods in days, weeks, months and years.
        Period p1 = Period.ofDays(7);
        Period p2 = Period.ofWeeks(2);
        Period p3 = Period.ofMonths(1);
        Period p4 = Period.ofYears(1);
        Period p5 = Period.of(1, 1, 7);

        // Obtains current date and add some period to the current date using 
        // the plus() method.
        LocalDate now = LocalDate.now();
        LocalDate date1 = now.plus(p1);
        LocalDate date2 = now.plus(p2);
        LocalDate date3 = now.plus(p3);
        LocalDate date4 = now.plus(p4);
        LocalDate date5 = now.plus(p5);

        // Print out the result of adding some period to the current date.
        System.out.printf("Add some period to the date: %s%n", now);
        System.out.printf("Plus %7s = %s%n", p1, date1);
        System.out.printf("Plus %7s = %s%n", p2, date2);
        System.out.printf("Plus %7s = %s%n", p3, date3);
        System.out.printf("Plus %7s = %s%n", p4, date4);
        System.out.printf("Plus %7s = %s%n%n", p5, date5);

        // Subtract some period from the date using the minus() method.
        System.out.printf("Subtract some period from the date: %s%n", now);
        System.out.printf("Minus %7s = %s%n", p1, now.minus(p1));
        System.out.printf("Minus %7s = %s%n", p2, now.minus(p2));
        System.out.printf("Minus %7s = %s%n", p3, now.minus(p3));
        System.out.printf("Minus %7s = %s%n", p4, now.minus(p4));
        System.out.printf("Minus %7s = %s%n%n", p5, now.minus(p5));
    }
}

And here are the result of the code snippet above:

Add some period to the date: 2021-11-16
Plus     P7D = 2021-11-23
Plus    P14D = 2021-11-30
Plus     P1M = 2021-12-16
Plus     P1Y = 2022-11-16
Plus P1Y1M7D = 2022-12-23

Subtract some period from the date: 2021-11-16
Minus     P7D = 2021-11-09
Minus    P14D = 2021-11-02
Minus     P1M = 2021-10-16
Minus     P1Y = 2020-11-16
Minus P1Y1M7D = 2020-10-09