How do I determine if a date falls between two dates?

Java provides different ways to determine if a certain date falls within a specified range. In this article, we’ll look at examples using the old java.util.Date and java.util.Calendar classes, as well as the newer Java Date Time API.

Using java.util.Date and java.util.Calendar

Before Java 8, you’d have to use Date or Calendar to work with dates:

package org.kodejava.datetime;

import java.util.Calendar;

public class CheckDateRange {
    public static void main(String[] args) {
        Calendar start = Calendar.getInstance();
        start.set(2024, Calendar.JANUARY, 1);
        Calendar end = Calendar.getInstance();
        end.set(2024, Calendar.DECEMBER, 31);
        Calendar target = Calendar.getInstance();
        target.set(2024, Calendar.JUNE, 15);

        if ((target.after(start) || target.equals(start)) &&
            (target.before(end) || target.equals(end))) {
            System.out.println("The date is within the range.");
        } else {
            System.out.println("The date is not within the range.");
        }
    }
}

The disadvantage with this approach is the excessive verbosity and error-prone copy-pasting necessary for setting up the Calendar instances.

The Java 8 Way – Using java.time.LocalDate

Java 8 introduced the new Java Date Time API, which replaced the inconsistent Date and Calendar classes with the more intuitive LocalDate, LocalTime, LocalDateTime, and ZonedDateTime. Here’s the same task performed using LocalDate:

package org.kodejava.datetime;

import java.time.LocalDate;

public class AnotherCheckDateRange {
    public static void main(String[] args) {
        LocalDate startDate = LocalDate.of(2024, 1, 1);
        LocalDate endDate = LocalDate.of(2024, 12, 31);
        LocalDate targetDate = LocalDate.of(2024, 6, 15);

        if ((!targetDate.isBefore(startDate)) && (!targetDate.isAfter(endDate))) {
            System.out.println("The date is within the range.");
        } else {
            System.out.println("The date is not within the range.");
        }
    }
}

In this code, startDate and endDate define the range of dates. The targetDate is the date you want to check.

The isBefore() method returns true if the targetDate is before the startDate, and the isAfter() method returns true if the targetDate is after the endDate. So, if targetDate is not before the startDate and not after the endDate, it means that the targetDate is between startDate and endDate (inclusive). If the targetDate is exactly the same as startDate or endDate, this condition will also return true.

This simplified API requires significantly less code and eliminates a number of potential bugs and inconsistencies.

Conclusion

The older java.util.Date and java.util.Calendar facilities for working with dates are widely considered difficult to use and error-prone. While they work for simple tasks, the newer Java Date Time API is recommended for all new applications due to its simplicity, consistency, and flexibility. It aligns with ISO standards and covers a comprehensive range of use-cases needed for date-time calculations. Migrating from older APIs to Java 8 Date Time API is likely advantageous for most projects.

How do I convert LocalDate to ZonedDateTime?

You can use the atStartOfDay() method from LocalDate class to convert a LocalDate into a LocalDateTime. Then, you need to convert LocalDateTime to a ZonedDateTime using the atZone() method.

Here is an example:

package org.kodejava.datetime;

import java.time.*;

public class LocalDateToZonedDateTimeExample {
    public static void main(String[] args) {
        // Create a LocalDate
        LocalDate date = LocalDate.of(2023, Month.JULY, 9);
        System.out.println("LocalDate: " + date);

        // Convert LocalDate to LocalDateTime
        LocalDateTime dateTime = date.atStartOfDay();
        System.out.println("LocalDateTime: " + dateTime);

        // Convert LocalDateTime to ZonedDateTime
        ZonedDateTime zonedDateTime = dateTime.atZone(ZoneId.systemDefault());
        System.out.println("ZonedDateTime: " + zonedDateTime);
    }
}

Output:

LocalDate: 2023-07-09
LocalDateTime: 2023-07-09T00:00
ZonedDateTime: 2023-07-09T00:00+08:00[Asia/Makassar]

In this example, we’re creating a LocalDate for July 9, 2023. Then we’re converting it to a LocalDateTime, and then to a ZonedDateTime. The atStartOfDay() method returns a LocalDateTime set to the start of the day (00:00) on the date of this LocalDate. The atZone() method then takes the ZoneId and returns a ZonedDateTime representing the start of the day in that timezone.

The ZoneId.systemDefault() returns the system default time zone. If you want to convert it to a specific time zone, you can specify the timezone as a string, like this: ZoneId.of("America/New_York").

How do I use java.time.Instant class of Java Date-Time API?

The java.time.Instant class in the Java Date-Time API is an immutable representation of a point in time. It stores a long count of seconds from the epoch of the first moment of 1970 UTC, plus a number of nanoseconds for the further precision within that second.

The java.time.LocalDate class represents a date without a time or time zone. It is used to represent just a date as year-month-day (e.g., 2023-03-27) in the ISO-8601 calendar system.

The java.time.LocalTime class represents a time without a date or time zone. It is used to represent just a time as hour-minute-second (e.g., 13:45:20).

It’s also worth noting that Instant class is part of Java 8’s new date and time API which was brought in to address the shortcomings of the old java.util.Date and java.util.Calendar API.

Here’s a quick example of how to use the Instant class:

package org.kodejava.datetime;

import java.time.Instant;

public class InstantExample {
    public static void main(String[] args) {
        // Get the current point in time
        Instant now = Instant.now();
        System.out.println("Current time: " + now);

        // Add duration of 500 seconds from now
        Instant later = now.plusSeconds(500);
        System.out.println("500 seconds later: " + later);

        // Subtract duration of 500 seconds from now
        Instant earlier = now.minusSeconds(500);
        System.out.println("500 seconds earlier: " + earlier);

        // Compare two Instants
        int comparison = now.compareTo(later);
        if (comparison < 0) {
            System.out.println("Now is earlier than later");
        } else if (comparison > 0) {
            System.out.println("Now is later than later");
        } else {
            System.out.println("Now and later are at the same time");
        }
    }
}

Output:

Current time: 2024-01-18T09:26:56.152268Z
500 seconds later: 2024-01-18T09:35:16.152268Z
500 seconds earlier: 2024-01-18T09:18:36.152268Z
Now is earlier than later

In this example, Instant.now() is used to get the current Instant. Various methods like plusSeconds(), minusSeconds(), and compareTo() are used to manipulate and compare the Instant.

LocalDate and LocalTime are local in the sense that they represent date and time from the context of the observer, without a time zone.

To connect Instant with LocalDate and LocalTime, you need a time zone. This is because Instant is in UTC and LocalDate/LocalTime are in a local time zone, so you need to explicitly provide a conversion between them.

Here’s how you convert an Instant to a LocalDate and a LocalTime:

package org.kodejava.datetime;

import java.time.*;

public class InstantConvertExample {
    public static void main(String[] args) {
        Instant now = Instant.now();
        System.out.println("Instant: " + now);

        // Get the system default timezone
        ZoneId zoneId = ZoneId.systemDefault(); 

        LocalDate localDate = now.atZone(zoneId).toLocalDate();
        System.out.println("LocalDate: " + localDate);

        LocalTime localTime = now.atZone(zoneId).toLocalTime();
        System.out.println("LocalTime: " + localTime);
    }
}

Here Instant.now() gives the current timestamp. .atZone(ZoneId.systemDefault()) converts it to ZonedDateTime which is then converted to LocalDate and LocalTime by using .toLocalDate() and .toLocalTime() respectively.

You can also go from LocalDate and LocalTime back to Instant. Here’s how:

package org.kodejava.datetime;

import java.time.*;

public class ToInstantExample {
    public static void main(String[] args) {
        LocalDate localDate = LocalDate.now();
        LocalTime localTime = LocalTime.now();
        ZoneId zoneId = ZoneId.systemDefault();
        Instant instantFromDateAndTime = LocalDateTime.of(localDate, localTime).atZone(zoneId).toInstant();

        System.out.println("Instant from LocalDate and LocalTime: " + instantFromDateAndTime);
    }
}

How do I use TemporalAdjusters dayOfWeekInMonth() method?

dayOfWeekInMonth() is a handy method in java.time.temporal.TemporalAdjusters class that returns an adjuster which changes the date to the n-th day of week in the current month.

Here is an example of how you could use it:

package org.kodejava.datetime;

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.temporal.TemporalAdjusters;

public class DayOfWeekInMonthExample {
    public static void main(String[] args) {
        // Current date
        LocalDate date = LocalDate.now();

        // The 2nd Tuesday in the month of the date.
        LocalDate secondTuesday = date.with(
                TemporalAdjusters.dayOfWeekInMonth(2, DayOfWeek.TUESDAY));

        System.out.println("Current Date: " + date);
        System.out.println("Second Tuesday: " + secondTuesday);
    }
}

Output:

Current Date: 2024-01-18
Second Tuesday: 2024-01-09

This code would display the date of the second Tuesday in the current month.

Here’s what’s going on in this case:

  • TemporalAdjusters.dayOfWeekInMonth(2, DayOfWeek.TUESDAY) specifies that we want the second occurrence of DayOfWeek.TUESDAY in the current month.

  • date.with(TemporalAdjuster) modifies the LocalDate date based on the TemporalAdjuster that is passed in. The original date object is unchanged; a new LocalDate reflecting the adjusted date is returned.

This TemporalAdjusters method is very useful when you have conditional logic based on things like “if it’s the third Monday of the month, then…”

How do I use java.time.Period class?

java.time.Period is a class that represents a quantity or amount of time in terms of years, months, and days. Here’s a brief guide on how to use it:

1. Creating a Period instance

The Period class provides several static methods named of() and between() to create an instance. To create Period of 1 year, 2 months, and 3 days:

Period period = Period.of(1, 2, 3);

Or you can create a Period using LocalDate:

LocalDate start = LocalDate.of(2020, Month.JANUARY, 1);
LocalDate end = LocalDate.of(2023, Month.MARCH, 31);
Period period = Period.between(start, end);

2. Retrieving Years, Months, and Days

Use the getDays(), getMonths(), and getYears() methods to get the number of days, months, and years in the Period.

int days = period.getDays();
int months = period.getMonths();
int years = period.getYears();

3. Adding/subtracting Period to/from a LocalDate

The LocalDate.plus() or LocalDate.minus() methods can be used to add or subtract a Period from a LocalDate.

LocalDate ld = LocalDate.of(2021, Month.JULY, 1);
Period period = Period.of(1, 2, 3);
LocalDate newDate = ld.plus(period);

In this case, newDate will be 1 year, 2 months, and 3 days after July 1, 2021.

4. Mixing units of time

You can use plusDays(), plusMonths(), or plusYears() to add to a Period.

Period period = Period.of(1, 2, 3);
Period newPeriod = period.plusDays(10);

The newPeriod will then be 1 year, 2 months, and 13 days.