How do I calculate difference between two dates?

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.

Besides 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.example.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 20 years, 5 months and 5 days old.
Diff in years  = 20
Diff in months = 245
Diff in days   = 7463

How do I know if a given year is a leap year?

The example How do I check if a year is a leap year? use the java.util.Calendar object to determine if a given year is a leap year. That was a the way to do it using the old API before we have the Date and Time API introduced in Java 8.

Now, in the Java 8 API we can check if a given year is a leap year using a couple of ways. We can determine if a given date is in a leap year by calling the isLeapYear() method of the java.time.LocalDate class. While using the java.time.Year class we can check is the given year if a leap year using the isLeap() method.

The following code snippet will show you how to do it:

package org.kodejava.example.datetime;

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

public class YearIsLeapExample {
    public static void main(String[] args) {
        // Using the java.time.LocalDate class.
        LocalDate now = LocalDate.now();
        boolean isLeap = now.isLeapYear();
        System.out.printf("Year %d, leap year = %s%n", now.getYear(), isLeap);

        LocalDate date = LocalDate.of(2012, Month.JANUARY, 1);
        isLeap = date.isLeapYear();
        System.out.printf("Year %d, leap year = %s%n", date.getYear(), isLeap);

        // Using the java.time.Year class.
        Year year = Year.now();
        isLeap = year.isLeap();
        System.out.printf("Year %d, leap year = %s%n", year.getValue(), isLeap);

        Year anotherYear = Year.of(2012);
        isLeap = anotherYear.isLeap();
        System.out.printf("Year %d, leap year = %s%n", anotherYear.get(ChronoField.YEAR), isLeap);
    }
}

The code snippet will print out the following result:

Year 2015, leap year = false
Year 2012, leap year = true
Year 2015, leap year = false
Year 2012, leap year = true

How do I convert Date to String?

package org.kodejava.example.text;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Calendar;
import java.util.Date;

public class DateToString {
    public static void main(String[] args) {
        // Create an instance of SimpleDateFormat used for formatting
        // the string representation of date (day/month/year)
        String pattern = "dd/MM/yyyy";
        DateFormat df = new SimpleDateFormat(pattern);

        // Get the date today using Calendar object.
        Date today = Calendar.getInstance().getTime();

        // Using DateFormat format method we can create a string
        // representation of a date with the defined format.
        String reportDate = df.format(today);

        // Print what date is today!
        System.out.println("Report Date: " + reportDate);

        // Using Java 8.
        // Creates a DateTimeFormatter using the ofPattern() method. Get
        // the current date by calling the .now() method of LocalDate.
        // To convert to string use the format() method of the LocalDate
        // and pass the formatter object as argument.
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
        LocalDate now = LocalDate.now();
        reportDate = now.format(formatter);
        System.out.println("Report Date: " + reportDate);
    }
}