The code below show you how to use the Months class to calculate the different in months between two dates.

package org.kodejava.joda;

import org.joda.time.DateMidnight;
import org.joda.time.LocalDate;
import org.joda.time.Months;

import java.util.Date;

public class MonthsBetweenDemo {
    public static void main(String[] args) {
        // Creates an instance of start and end dates.
        DateMidnight start = new DateMidnight("2021-01-01");
        DateMidnight end = new DateMidnight(new Date());

        // Get months between these dates.
        int months = Months.monthsBetween(start, end).getMonths();

        // Print the result.
        System.out.println("Months between " +
                start.toString("yyyy-MM-dd") + " and " +
                end.toString("yyyy-MM-dd") + " = " +
                months + " month(s)");

        // Using LocalDate object.
        LocalDate date1 = LocalDate.parse("2021-03-01");
        LocalDate date2 = LocalDate.now();
        months = Months.monthsBetween(date1, date2).getMonths();

        // Print the result.
        System.out.println("Months between " +
                date1.toString("yyyy-MM-dd") + " and " +
                date2.toString("yyyy-MM-dd") + " = " +
                months + " month(s)");
    }
}

Here is the output of our program:

Months between 2021-01-01 and 2021-10-29 = 9 month(s)
Months between 2021-03-01 and 2021-10-29 = 7 month(s)

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>

This example show us how to use Joda-Time’s DateTime class to get the last day of the month. To get the last day of the month we first need to find out the last date of the month. To do this, create a new instance of a DateTime. From the DateTime object get the day-of-the-month property by calling the dayOfMonth() method. Then call the withMaximumValue() method which will give us the last date of a month.

To get the day name, we call the DateTime‘s dayOfWeek() method followed by a call to the getAsText() method to get the name of the day. Let’s see the code snippet below:

package org.kodejava.joda;

import org.joda.time.DateTime;
import org.joda.time.LocalDate;

public class LastDayOfTheMonth {
    public static void main(String[] args) {
        // Creates an instance of DateTime.
        DateTime dateTime = DateTime.now();

        // Get the last date of the month using the dayOfMonth property
        // and get the maximum value from it.
        DateTime lastDate = dateTime.dayOfMonth().withMaximumValue();

        // Print the date and day name.
        System.out.println("Last date of the month = " + lastDate);
        System.out.println("Last day of the month  = " +
                lastDate.dayOfWeek().getAsText());

        // If you know the last date of the month you can simply parse the
        // date string and get the name of the last day of the month.
        String day = LocalDate.parse("2021-10-31").dayOfWeek().getAsText();
        System.out.println("Day  = " + day);
    }
}

If you know the last date of the month you can simply parse the date string to create a DateTime object or a LocalDate object and call the dayOfWeek() method and get the name of the day using getAsText() method.

The example output is:

Last date of the month = 2021-10-31T06:37:18.069+08:00
Last day of the month  = Sunday
Day  = Sunday

Maven Dependencies

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

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>