This code snippet show you how to convert Joda-Time’s DateTime object into JDK’s java.util.Calendar or java.util.Date object. To convert DateTime to java.util.Date we use the toDate() method and to convert to java.util.Calendar we use the toCalendar() method.

package org.kodejava.joda;

import org.joda.time.DateTime;

import java.util.Calendar;
import java.util.Date;
import java.util.Locale;

public class DateTimeToDateCalendarDemo {
    public static void main(String[] args) {
        // Converting DateTime object into JDK's Date.
        DateTime dateTime = DateTime.now();
        Date date = dateTime.toDate();
        System.out.println("org.joda.time.DateTime = " + dateTime);
        System.out.println("java.util.Date         = " + date);

        // Converting DateTime object into JDK's Calendar.
        Calendar calendar = dateTime.toCalendar(Locale.getDefault());
        System.out.println("java.util.Calendar     = " + calendar);
    }
}

The result of our code snippet:

org.joda.time.DateTime = 2021-10-29T06:54:29.003+08:00
java.util.Date         = Fri Oct 29 06:54:29 CST 2021
java.util.Calendar     = java.util.GregorianCalendar[time=1635461669003,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=9,WEEK_OF_YEAR=44,WEEK_OF_MONTH=5,DAY_OF_MONTH=29,DAY_OF_YEAR=302,DAY_OF_WEEK=6,DAY_OF_WEEK_IN_MONTH=5,AM_PM=0,HOUR=6,HOUR_OF_DAY=6,MINUTE=54,SECOND=29,MILLISECOND=3,ZONE_OFFSET=28800000,DST_OFFSET=0]

Maven Dependencies

<dependency>
    <groupId>joda-time</groupId>
    <artifactId>joda-time</artifactId>
    <version>2.12.5</version>
</dependency>

Using the Joda-Time library can simplify the date calculation process. For instance, we can add or subtract some days, weeks, months or year easily. There are a plus and minus method for this operation. For instance if you want to add 9 weeks to date object you can do something like date.plusWeeks(9).

package org.kodejava.joda;

import org.joda.time.LocalDate;

public class DateCalculationDemo {
    public static void main(String[] args) {
        // Creates an instance of LocalDate where we are going to do
        // some date calculations.
        LocalDate date = new LocalDate(2021, 10, 29);
        System.out.println("Date           = " + date);

        // Add days, weeks, months, year value into the date object.
        System.out.println("plusDays(10)   = " + date.plusDays(10));
        System.out.println("plusWeeks(9)   = " + date.plusWeeks(9));
        System.out.println("plusMonths(2)  = " + date.plusMonths(2));
        System.out.println("plusYears(1)   = " + date.plusYears(1));

        // Subtract days, weeks, months, year value from date object.
        System.out.println("minusDays(10)  = " + date.minusDays(10));
        System.out.println("minusWeeks(9)  = " + date.minusWeeks(9));
        System.out.println("minusMonths(2) = " + date.minusMonths(2));
        System.out.println("minusYears(1)  = " + date.minusYears(1));
    }
}

The output of the program above are:

Date           = 2021-10-29
plusDays(10)   = 2021-11-08
plusWeeks(9)   = 2021-12-31
plusMonths(2)  = 2021-12-29
plusYears(1)   = 2022-10-29
minusDays(10)  = 2021-10-19
minusWeeks(9)  = 2021-08-27
minusMonths(2) = 2021-08-29
minusYears(1)  = 2020-10-29

Maven Dependencies

<dependency>
    <groupId>joda-time</groupId>
    <artifactId>joda-time</artifactId>
    <version>2.12.5</version>
</dependency>

The example show you how to format the string representation of a date. In Joda we can use the DateTime‘s class toString() method. The method accept the pattern of the date format and the locale information.

package org.kodejava.joda;

import org.joda.time.DateTime;
import org.joda.time.format.DateTimeFormat;

import java.util.Locale;

public class FormattingDemo {
    // Define the date format pattern.
    private static final String pattern = "E MM/dd/yyyy HH:mm:ss.SSS";

    public static void main(String[] args) {
        // Creates a new instance of DateTime object.
        DateTime dt = DateTime.now();

        // Print out the date as a formatted string using the defined
        // Locale information.
        System.out.println("Pattern  = " + pattern);
        System.out.println("Default  = " + dt.toString(pattern));
        System.out.println("Germany  = " + dt.toString(pattern, Locale.GERMANY));
        System.out.println("French   = " + dt.toString(pattern, Locale.FRENCH));
        System.out.println("Japanese = " + dt.toString(pattern, Locale.JAPANESE));

        // Using predefined format from DateTimeFormat class.
        System.out.println("fullDate   = " + dt.toString(DateTimeFormat.fullDate()));
        System.out.println("longDate   = " + dt.toString(DateTimeFormat.longDate()));
        System.out.println("mediumDate = " + dt.toString(DateTimeFormat.mediumDate()));
        System.out.println("shortDate  = " + dt.toString(DateTimeFormat.shortDate()));
        System.out.println("dd/MM/yyyy = " + dt.toString(DateTimeFormat.forPattern("dd/MM/yyyy")));
    }
}

Here are the example result of our program:

Pattern  = E MM/dd/yyyy HH:mm:ss.SSS
Default  = Fri 10/29/2021 06:49:32.491
Germany  = Fr. 10/29/2021 06:49:32.491
French   = ven. 10/29/2021 06:49:32.491
Japanese = 金 10/29/2021 06:49:32.491
fullDate   = Friday, October 29, 2021
longDate   = October 29, 2021
mediumDate = Oct 29, 2021
shortDate  = 10/29/21
dd/MM/yyyy = 29/10/2021

Maven Dependencies

<dependency>
    <groupId>joda-time</groupId>
    <artifactId>joda-time</artifactId>
    <version>2.12.5</version>
</dependency>

In Joda-Time the date and time information are divided into fields. The following example show you some fields that can be obtained from the DateTime object. For example to get the day of the year we use the getDayOfYear() method and to get the day of week we can use the getDayOfWeek() method.

package org.kodejava.joda;

import org.joda.time.DateTime;

public class DateTimeFieldDemo {
    public static void main(String[] args) {
        DateTime dateTime = new DateTime();
        System.out.println("DateTime          = " + dateTime);

        // Get day of year, day of month, day of week and week of
        // year of a date.
        System.out.println("Day of Year       = " + dateTime.getDayOfYear());
        System.out.println("Day of Month      = " + dateTime.getDayOfMonth());
        System.out.println("Day of Week       = " + dateTime.getDayOfWeek());
        System.out.println("Week of Week year = " + dateTime.getWeekOfWeekyear());

        // Get hour of day, minute of hour and second of minute.
        System.out.println("Hour of Day       = " + dateTime.getHourOfDay());
        System.out.println("Minute of Hour    = " + dateTime.getMinuteOfHour());
        System.out.println("Second of Minute  = " + dateTime.getSecondOfMinute());

        // Get minute of day and second of day.
        System.out.println("Minute of Day     = " + dateTime.getMinuteOfDay());
        System.out.println("Second of Day     = " + dateTime.getSecondOfDay());
    }
}

The outputs of our program are:

DateTime          = 2021-10-29T06:46:49.259+08:00
Day of Year       = 302
Day of Month      = 29
Day of Week       = 5
Week of Week year = 43
Hour of Day       = 6
Minute of Hour    = 46
Second of Minute  = 49
Minute of Day     = 406
Second of Day     = 24409

Maven Dependencies

<dependency>
    <groupId>joda-time</groupId>
    <artifactId>joda-time</artifactId>
    <version>2.12.5</version>
</dependency>

This example will give you the first day of the next month from the current system date. In the example we use the MutableDateTime class. MutableDateTime is a datetime class whose value can be modified.

In the code snippet we start by creating an instance of MutableDateTime class. We add 1 month from the current date using the addMonths() method. We set the day of the month to the first day using the setDayOfMonth() method. To make sure it is the first day we set the time to midnight by calling the setMillisOfDay() method.

package org.kodejava.joda;

import org.joda.time.MutableDateTime;

public class FirstDayOfNextMonth {
    public static void main(String[] args) {
        // Creates an instance of MutableDateTime for the current
        // system date time.
        MutableDateTime dateTime = new MutableDateTime();
        System.out.println("Current date            = " + dateTime);

        // Find the first day of the next month can be done by:
        // 1. Add 1 month to the date
        // 2. Set the day of the month to 1
        // 3. Set the millis of day to 0.
        dateTime.addMonths(1);
        dateTime.setDayOfMonth(1);
        dateTime.setMillisOfDay(0);
        System.out.println("First day of next month = " + dateTime);
    }
}

Here is an example result of the program:

Current date            = 2021-10-29T06:40:17.373+08:00
First day of next month = 2021-11-01T00:00:00.000+08:00

Maven Dependencies

<dependency>
    <groupId>joda-time</groupId>
    <artifactId>joda-time</artifactId>
    <version>2.12.5</version>
</dependency>