Date Diff and Date Add

Finding the number  of years, months, days, minutes, seconds, or milliseconds between two date times can be a hard task for beginners. In this post, you will learn how to calculate the difference in days between two date times and to calculate the future and past dates from the current date. These tasks can be done simply by using the Joda-Time library. It is the most useful library to work with date and times. You will need to download this library from Joda-Time website. You will get a zip file. Please extract the zip file to a folder that you can file.

To use the Joda-Time library in your code, you need to add the jar file (joda-time-2.2.jar) to the build path of the Eclipse. You can follow the step below to add the library to the project in Eclipse.
1. From the Project menu, select Properties.
2. On the properties window, select Java Build Path. Then select Add External Jars...

3. Browse to find the jar file that you have extracted. Then click OK.

If you are using the Windows' command prompt to compile and run your java program, you will need to the add the path of the jar file to the CLASSPATH by going to the Control Panel->System->Advanced System Settings. In the System Properties dialog, select Environment Variables. In the box under User variables, double-click CLASSPATH. Then append the path of the jar file to the Variable value text box. You will use the semi-colon (;) to separate each path entry.

Now you are ready to use the Jodatime library. To calculate the difference between two date times, you can use the Years.Years.yearsBetween, Months.monthsBetween, Days.daysBetween, Hours.hoursBetween, Minutes.minutesBetween, Seconds.secondsBetween methods. The example code below calculates the days and hours between the current and another future date.

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import org.joda.time.DateTime;
import org.joda.time.Days;
import org.joda.time.Hours;

public class DateDiff {
public static void main(String[] args){
DateFormat formatter = new SimpleDateFormat("dd-MM-yyyyy");

Date futureDate=null;
Date today = Calendar.getInstance().getTime();

try{
futureDate= formatter.parse("30-10-2013");
}
catch(ParseException pe)    {
   System.out.println("Parser Exception");
}

Days days = Days.daysBetween(new DateTime(today),new DateTime(futureDate));
Hours hours=Hours.hoursBetween(new DateTime(today), new DateTime(futureDate));
System.out.println(" Days Between " + today + " and " + futureDate + " :" + days.getDays());
System.out.println(" Hours Between " + today + " and " + futureDate + " :" + hours.getHours());


}
}

If you would like to calculate the future date by adding a number of years, months, days, hours, minutes, seconds, or milliseconds to the current date, you will use the plusYears, plusMonths, plusDays, plusHours, plusMinutes, plusSeconds, or plusMillis methods of the DateTime class. Similarly, to find the past date, you can use the minusYears, minusMonths, minusDays, minusHours, minusMinutes, minusSeconds, or minusMillis methods. Read the example code below.


import java.util.Calendar;
import java.util.Date;
import org.joda.time.DateTime;

public class DateAdd{
public static void main(String[] args){
Date today = Calendar.getInstance().getTime();
DateTime dt=new DateTime(today);
DateTime futureDate=dt.plusDays(2); //add two days to the current date
System.out.println("The future date is "+futureDate);


}
}