The following code snippet show you how to get days between two dates. You can use the Days.daysBetween() method and pass the dates you want to calculate. This method return a Days object. To get the number in days you call the getDays() method.

package org.kodejava.joda;

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

public class DaysBetweenDemo {
    public static void main(String[] args) {
        // Define the start and end dates. We use the DateMidnight
        // class to make sure that the calculation start from the
        // midnight.
        DateMidnight start = new DateMidnight("2021-07-01");
        DateMidnight end = new DateMidnight("2021-07-22");

        // Get days between the start date and end date.
        int days = Days.daysBetween(start, end).getDays();

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

        // Using LocalDate object.
        LocalDate date1 = LocalDate.parse("2021-07-01");
        LocalDate date2 = LocalDate.now();
        days = Days.daysBetween(date1, date2).getDays();

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

Here is the result of the program:

Days between 2021-07-01 and 2021-07-22 = 21 day(s)
Days between 2021-07-01 and 2021-10-29 = 120 day(s)

To calculate differences between two date objects in Java 8 see the following example: How do I calculate difference between two dates?.

Maven Dependencies

<dependency>
    <groupId>joda-time</groupId>
    <artifactId>joda-time</artifactId>
    <version>2.12.7</version>
</dependency>

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>

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>