How to compare dates in ISO8601 format?

Question

Is there a way to compare ISO8601 dates with Java? Like, to know if the String date is the good format, to know if months are not negative and not >12, to know if days are not over 31, when %4 if february doesn't have over 29 days...

I'm also searching how to know if there is a class on the Internet to compare two ISO8601 dates? Like, if I have: 2000-12-12 and 1999-05-06. How can I compare those two dates to have the exact difference between years, months and days?

Answer 1

Is there a way to compare ISO8601 dates with Java? Like, to know if the String date is the good format, to know if months are not negative and not >12, to know if days are not over 31, when %4 if february doesn't have over 29 days...

Get a LocalDate instance on passing the year, the month and the day of the month as parameters to LocalDate.of inside a try-catch block. If any of these will be invalid, DateTimeException will be thrown indicating the same.

Demo

import java.time.DateTimeException;
import java.time.LocalDate;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int year, month, dayOfMonth;
        LocalDate date;
        System.out.print("Enter the year, month and day separated by space: ");
        year = scanner.nextInt();
        month = scanner.nextInt();
        dayOfMonth = scanner.nextInt();

        try {
            date = LocalDate.of(year, month, dayOfMonth);
            System.out.println("The date in ISO 8601 format is " + date);
        } catch (DateTimeException e) {
            System.out.println(e.getMessage());
        }
    }
}

A sample run:

Enter the year, month and day separated by space: 2020 2 30
Invalid date 'FEBRUARY 30'

Another sample run:

Enter the year, month and day separated by space: 2020 2 29
The date in ISO 8601 format is 2020-02-29

I'm also searching how to know if there is a class on the Internet to compare two ISO8601 dates? Like, if I have: 2000-12-12 and 1999-05-06. How can I compare those two dates to have the exact difference between years, months and days?

Use LocalDate#until to get java.time.Period from which you can get years, months and days.

Demo

import java.time.LocalDate;
import java.time.Period;

public class Main {
    public static void main(String[] args) {
        String dateStr1 = "1999-05-06";
        String dateStr2 = "2000-12-12";

        LocalDate date1 = LocalDate.parse(dateStr1);
        LocalDate date2 = LocalDate.parse(dateStr2);

        Period period = date1.until(date2);
        System.out.printf("There are %d years, %d months and %d days between %s and %s", period.getYears(),
                period.getMonths(), period.getDays(), dateStr1, dateStr2);
    }
}

Output:

There are 1 years, 7 months and 6 days between 1999-05-06 and 2000-12-12