How do I create a custom TemporalAdjuster?

By Wayan in Date Time 0 Comment

In this example we are going to learn how to implement a custom TemporalAdjuster. We are going to create TemporalAdjuster to find the next working day from a specified date. We will use 5 working days, from Monday to Friday.

The custom temporal adjuster class should implement the TemporalAdjuster interface, which define a single method that we must implement, the adjustInto(Temporal) method.

package org.kodejava.datetime;

import java.time.DayOfWeek;
import java.time.temporal.ChronoField;
import java.time.temporal.ChronoUnit;
import java.time.temporal.Temporal;
import java.time.temporal.TemporalAdjuster;

public class NextWorkingDayAdjuster implements TemporalAdjuster {
    @Override
    public Temporal adjustInto(Temporal temporal) {
        int field = temporal.get(ChronoField.DAY_OF_WEEK);
        DayOfWeek dayOfWeek = DayOfWeek.of(field);

        int daysToAdd = 1;
        if (DayOfWeek.FRIDAY.equals(dayOfWeek)) {
            daysToAdd = 3;
        } else if (DayOfWeek.SATURDAY.equals(dayOfWeek)) {
            daysToAdd = 2;
        }
        return temporal.plus(daysToAdd, ChronoUnit.DAYS);
    }
}

The NextWorkingDayAdjuster move the temporal object a day forward. Except if it is on Friday or Saturday, which will move the temporal object three days or two days forward respectively. This will make it return Monday as the next working day.

After creating the custom adjuster, now let’s create an example that use the NextWorkingDayAdjuster class.

package org.kodejava.datetime;

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

public class NextWorkingDayAdjusterDemo {
    public static void main(String[] args) {
        TemporalAdjuster nextWorkingDay = new NextWorkingDayAdjuster();

        LocalDate now = LocalDate.now();
        LocalDate nextDay = now.with(nextWorkingDay);
        System.out.println("now            = " + now);
        System.out.println("nextWorkingDay = " + nextDay);

        LocalDate friday = LocalDate.of(2021, Month.MARCH, 11);
        nextDay = friday.with(nextWorkingDay);
        System.out.println("friday         = " + friday);
        System.out.println("nextWorkingDay = " + nextDay);

        LocalDate saturday = LocalDate.of(2021, Month.MARCH, 12);
        nextDay = saturday.with(nextWorkingDay);
        System.out.println("saturday       = " + saturday);
        System.out.println("nextWorkingDay = " + nextDay);
    }
}

And here are the results of our code:

now            = 2021-11-18
nextWorkingDay = 2021-11-19
friday         = 2021-03-11
nextWorkingDay = 2021-03-12
saturday       = 2021-03-12
nextWorkingDay = 2021-03-15

How do I manipulate LocalDate object using TemporalAdjuster?

By Wayan in Date Time 0 Comment

In the previous example we manipulate the value of LocalDate by adding or subtracting the value of date object by days, months, years using methods like plusMonths() or minusDays(). Or by changing the year or the month of the date object using methods like withYear() or withMonth().

But there are times that we want to manipulate the date object so that we can get the first day of the month or the last day of the month. We want to manipulate the date value to advance the date to the first Monday after the current day or the last the of the year.

To manipulate the date object in this way we can use the with() method and pass a TemporalAdjuster object as an argument. Fortunately, the Date and Time API already provide some commonly used TemporalAdjuster. These TemporalAdjuster are provided as a static factory methods that we can find in the java.time.temporal.TemporalAdjusters class.

The following example is a code snippet to manipulate the date object using TemporalAdjuster / TemporalAdjusters class.

package org.kodejava.datetime;

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

public class DateManipulationWithTemporalAdjuster {
    public static void main(String[] args) {
        LocalDate date = LocalDate.now();
        System.out.println("Current date       = " + date);

        LocalDate date1 = date.with(TemporalAdjusters.firstDayOfMonth());
        System.out.println("First day of month = " + date1);

        LocalDate date2 = date.with(TemporalAdjusters.lastDayOfMonth());
        System.out.println("Last day of month  = " + date2);

        LocalDate date3 = date.with(TemporalAdjusters.next(DayOfWeek.MONDAY));
        System.out.println("Next Monday        = " + date3);

        LocalDate date4 = date.with(TemporalAdjusters.lastDayOfYear());
        System.out.println("Last day of year   = " + date4);
    }
}

The result of the code snippet are:

Current date       = 2021-11-18
First day of month = 2021-11-01
Last day of month  = 2021-11-30
Next Monday        = 2021-11-22
Last day of year   = 2021-12-31

The table below shows the complete static factory methods provided by the TemporalAdjusters class.

Method Name Method Description
dayOfWeekInMonth Returns a new date in the same month with the ordinal day-of-week.
firstDayOfMonth Returns a new date set to the first day of the current month.
firstDayOfNextMonth Returns a new date set to the first day of the next month.
firstDayOfNextYear Returns a new date set to the first day of the next year.
firstDayOfYear Returns a new date set to the first day of the current year.
firstInMonth Returns a new date in the same month with the first matching day-of-week.
lastDayOfMonth Returns a new date set to the last day of the current month.
lastDayOfYear Returns a new date set to the last day of the current year.
lastInMonth Returns a new date in the same month with the last matching day-of-week.
next Returns the next day-of-week adjuster.
nextOrSame Returns the next-or-same day-of-week adjuster.
ofDateAdjuster Returns user-written adjuster.
previous Returns the previous day-of-week adjuster.
previousOrSame Returns the previous-or-same day-of-week adjuster.

How do I manipulate the value of LocalDate object?

By Wayan in Date Time 0 Comment

In the following example we will learn how to manipulate a LocalDate object. There are many methods available for us to change the value of a LocalDate object. For example, we can change the year, month and day of LocalDate object. We can use methods like withYear(), withDayOfMonth(), plusYears(), minusMonths(), etc. All these methods will return a new LocalDate object, the original LocalDate will stay unchanged.

Let’s see the following code example for demonstration on how to manipulate the value of LocalDate object.

package org.kodejava.datetime;

import java.time.LocalDate;
import java.time.Month;
import java.time.temporal.ChronoField;
import java.time.temporal.ChronoUnit;

public class LocalDateManipulation {
    public static void main(String[] args) {
        absoluteAttributeManipulations();
        relativeAttributeManipulations();
    }

    private static void absoluteAttributeManipulations() {
        System.out.println("LocalDateManipulation.absoluteAttributeManipulations");
        LocalDate date1 = LocalDate.of(2021, Month.JANUARY, 1);
        LocalDate date2 = date1.withYear(2010);
        LocalDate date3 = date2.withMonth(Month.DECEMBER.getValue());
        LocalDate date4 = date3.withDayOfMonth(15);
        LocalDate date5 = date4.with(ChronoField.DAY_OF_YEAR, 100);

        System.out.println("of(2021, Month.JANUARY, 1)                 => " + date1);
        System.out.println("date1.withYear(2010)                       => " + date2);
        System.out.println("date2.withMonth(Month.DECEMBER.getValue()) => " + date3);
        System.out.println("date3.withDayOfMonth(15)                   => " + date4);
        System.out.println("date4.with(ChronoField.DAY_OF_YEAR, 100)   => " + date5);
    }

    private static void relativeAttributeManipulations() {
        System.out.println("LocalDateManipulation.relativeAttributeManipulations");
        LocalDate date1 = LocalDate.of(2021, Month.AUGUST, 17);
        LocalDate date2 = date1.minusYears(70);
        LocalDate date3 = date2.plusMonths(10);
        LocalDate date4 = date3.minusDays(15);
        LocalDate date5 = date4.plusWeeks(52);
        LocalDate date6 = date5.minus(52, ChronoUnit.WEEKS);

        System.out.println("of(2021, Month.AUGUST, 17)        => " + date1);
        System.out.println("date1.minusYears(70)              => " + date2);
        System.out.println("date1.plusMonths(10)              => " + date3);
        System.out.println("date3.minusDays(15)               => " + date4);
        System.out.println("date4.plusWeeks(52)               => " + date5);
        System.out.println("date5.minus(52, ChronoUnit.WEEKS) => " + date6);

    }
}

The results of this code snippet are:

LocalDateManipulation.absoluteAttributeManipulations
of(2021, Month.JANUARY, 1)                 => 2021-01-01
date1.withYear(2010)                       => 2010-01-01
date2.withMonth(Month.DECEMBER.getValue()) => 2010-12-01
date3.withDayOfMonth(15)                   => 2010-12-15
date4.with(ChronoField.DAY_OF_YEAR, 100)   => 2010-04-10

LocalDateManipulation.relativeAttributeManipulations
of(2021, Month.AUGUST, 17)        => 2021-08-17
date1.minusYears(70)              => 1951-08-17
date1.plusMonths(10)              => 1952-06-17
date3.minusDays(15)               => 1952-06-02
date4.plusWeeks(52)               => 1953-06-01
date5.minus(52, ChronoUnit.WEEKS) => 1952-06-02

How to find the difference between two LocalDateTime objects?

By Wayan in Date Time 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 convert between old Date and Calendar object with the new Java 8 Date Time?

By Wayan in Date Time 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 Wayan in Date Time 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 2016. First let’s create a LocalDate object that represent the new year of 2016. 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 Wayan in Date Time 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

How do I calculate difference between two dates?

By Wayan in Date Time 1 Comment

In this example you’ll learn how to use the java.time.Period class (from Java 8) to calculate difference between two dates. Using Period.between() method will give us difference between two dates in years, months and days period.

Beside using the Period class, we also use the ChronoUnit enum to calculate difference between two dates. We use the ChronoUnit.YEARS, ChronoUnit.MONTHS and ChronoUnit.DAYS and call the between() method to get the difference between two dates in years, months and days.

Let’s see an example below.

package org.kodejava.datetime;

import java.time.LocalDate;
import java.time.Month;
import java.time.Period;
import java.time.temporal.ChronoUnit;

public class DateDifference {
    public static void main(String[] args) {
        LocalDate birthDate = LocalDate.of(1995, Month.AUGUST, 17);
        LocalDate now = LocalDate.now();

        // Obtains a period consisting of the number of years, months and days
        // between two dates.
        Period age = Period.between(birthDate, now);
        System.out.printf("You are now %d years, %d months and %d days old.%n",
                age.getYears(), age.getMonths(), age.getDays());

        // Using ChronoUnit to calculate difference in years, months and days
        // between two dates.
        long years = ChronoUnit.YEARS.between(birthDate, now);
        long months = ChronoUnit.MONTHS.between(birthDate, now);
        long days = ChronoUnit.DAYS.between(birthDate, now);

        System.out.println("Diff in years  = " + years);
        System.out.println("Diff in months = " + months);
        System.out.println("Diff in days   = " + days);
    }
}

The result of our code snippet above are:

You are now 26 years, 2 months and 30 days old.
Diff in years  = 26
Diff in months = 314
Diff in days   = 9588

How do I use the java.time.DayOfWeek enum?

By Wayan in Date Time 0 Comment

The java.time.DayOfWeek enums in Java 8 Date-Time API describes the days of the week. The enum has constants value from DayOfWeek.MONDAY through DayOfWeek.SUNDAY. These enums also have their integer values where 1 is equal to MONDAY and 7 is equal to SUNDAY.

In the code snippet below you can see a couple usage of the DayOfWeek enums. We start by getting all the enum values using the values() method that return an array of DayOfWeek. We iterate this array and print out the enum value and its corresponding integer value.

// Get DayOfWeek enums value
DayOfWeek[] dayOfWeeks = DayOfWeek.values();
for (int i = 0; i < dayOfWeeks.length; i++) {
    DayOfWeek dayOfWeek = dayOfWeeks[i];
    System.out.println("dayOfWeek[" + i + "] = " + dayOfWeek + "; value = " +
            dayOfWeek.getValue());
}

To create a DayOfWeek object we can use the of(int) factory method. We pass an integer value of this method. For example giving 1 will give us the DayOfWeek.MONDAY. We can also utilize enum valueOf(String) method to create enum from string value.

// Get DayOfWeek from int value
DayOfWeek dayOfWeek = DayOfWeek.of(1);
System.out.println("dayOfWeek = " + dayOfWeek);

// Get DayOfWeek from string value
dayOfWeek = DayOfWeek.valueOf("SATURDAY");
System.out.println("dayOfWeek = " + dayOfWeek);

To get the DayOfWeek from a date-time object we can use the getDayOfWeek() method. Below we get the day of week from a LocalDate object.

// Get DayOfWeek of a date object
LocalDate date = LocalDate.now();
DayOfWeek dow = date.getDayOfWeek();

System.out.println("Date  = " + date);
System.out.println("Dow   = " + dow + "; value = " + dow.getValue());

We can also get the day of week for a specific locale. To do this we can use the DayOfWeek.getDisplayName(TextStyle, Locale) method. The TextStyle can be of value TextStyle.FULL, TextStyle.SHORT, TextStyle.NARROW which will give us the full, short, and narrow version of the display name. The example below get the display name for Indonesian and German version.

// Get DayOfWeek display name in different locale.
Locale locale = new Locale("id", "ID");
String indonesian = dow.getDisplayName(TextStyle.SHORT, locale);
System.out.println("ID = " + indonesian);

String germany = dow.getDisplayName(TextStyle.FULL, Locale.GERMANY);
System.out.println("DE = " + germany);

There is also a plus(long) method that can be used to add number of days to a DayOfWeek object. For example adding 4 to MONDAY will give us DayOfWeek.FRIDAY.

// Adding number of days to DayOfWeek enum.
System.out.println("DayOfWeek.MONDAY.plus(4) = " + DayOfWeek.MONDAY.plus(4));

Here is the complete code for the snippets above:

package org.kodejava.datetime;

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.format.TextStyle;
import java.util.Locale;

public class DayOffWeekExample {
    public static void main(String[] args) {
        // Get DayOfWeek enums value
        DayOfWeek[] dayOfWeeks = DayOfWeek.values();
        for (int i = 0; i < dayOfWeeks.length; i++) {
            DayOfWeek dayOfWeek = dayOfWeeks[i];
            System.out.println("dayOfWeek[" + i + "] = " + dayOfWeek + "; value = " +
                    dayOfWeek.getValue());
        }

        // Get DayOfWeek from int value
        DayOfWeek dayOfWeek = DayOfWeek.of(1);
        System.out.println("dayOfWeek = " + dayOfWeek);

        // Get DayOfWeek from string value
        dayOfWeek = DayOfWeek.valueOf("SATURDAY");
        System.out.println("dayOfWeek = " + dayOfWeek);

        // Get DayOfWeek of a date object
        LocalDate date = LocalDate.now();
        DayOfWeek dow = date.getDayOfWeek();

        System.out.println("Date  = " + date);
        System.out.println("Dow   = " + dow + "; value = " + dow.getValue());

        // Get DayOfWeek display name in different locale.
        Locale locale = new Locale("id", "ID");
        String indonesian = dow.getDisplayName(TextStyle.SHORT, locale);
        System.out.println("ID = " + indonesian);

        String germany = dow.getDisplayName(TextStyle.FULL, Locale.GERMANY);
        System.out.println("DE = " + germany);

        // Adding number of days to DayOfWeek enum.
        System.out.println("DayOfWeek.MONDAY.plus(4) = " + DayOfWeek.MONDAY.plus(4));
    }
}

And the result of the code above are:

dayOfWeek[0] = MONDAY; value = 1
dayOfWeek[1] = TUESDAY; value = 2
dayOfWeek[2] = WEDNESDAY; value = 3
dayOfWeek[3] = THURSDAY; value = 4
dayOfWeek[4] = FRIDAY; value = 5
dayOfWeek[5] = SATURDAY; value = 6
dayOfWeek[6] = SUNDAY; value = 7
dayOfWeek = MONDAY
dayOfWeek = SATURDAY
Date  = 2021-11-16
Dow   = TUESDAY; value = 2
ID = Sel
DE = Dienstag
DayOfWeek.MONDAY.plus(4) = FRIDAY

How do I format date-time objects in Java 8?

By Wayan in Date Time 0 Comment

In your Java application you want to format date-time objects using the new date and time API introduced in JDK 8. A solution to this problem is to use the java.time.format.DateTimeFormatter. The DateTimeFormatter class provides formatter for printing and parsing date-time objects.

With this class we can format the date-time objects using a predefined constants, there are many predefined ready to use formats, such as ISO_DATE, ISO_DATE_TIME. You can also use letters pattern to format the date-time objects, for instance using the dd MMMM yyyy. The formatter can format in localized style, in a long or medium style.

Let’s see an example below:

package org.kodejava.datetime;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class DateTimeFormatterDemo {
    public static void main(String[] args) {
        // Get system current date and time.
        LocalDateTime time = LocalDateTime.now();

        // Get an instance of DateTimeFormatter and print a
        // formatted version of the system current date-time
        // using a predefined formatter.
        DateTimeFormatter format = DateTimeFormatter.ISO_DATE_TIME;
        System.out.printf("Time: %s%n", time.format(format));

        // Create a custom formatter and format the date-time
        // object.
        DateTimeFormatter customFormat =
                DateTimeFormatter.ofPattern("MMMM d, yyyy hh:mm a");
        System.out.printf("Time: %s%n", time.format(customFormat));

        // Create a custom formatter with locale and format the
        // date-time object.
        DateTimeFormatter localeFormat =
                DateTimeFormatter.ofPattern("d MMM yyyy HH:mm:ss",
                        Locale.FRENCH);
        System.out.printf("Time: %s%n", time.format(localeFormat));
    }
}

The results of the code above are:

Time: 2021-11-16T07:51:16.1247212
Time: November 16, 2021 07:51 AM
Time: 16 nov. 2021 07:51:16