Time Zone Handling

Part of the Logic & Flow section of Coddy's Java journey — lesson 59 of 59.

ZonedDateTime in Java represents a date and time with a time zone. It's useful when working with different time zones or converting between them.

Create a time in a specific zone:

ZonedDateTime tokyo = ZonedDateTime.now(ZoneId.of("Asia/Tokyo"));

You can also convert a LocalDateTime to a ZonedDateTime using .atZone():

LocalDateTime local = LocalDateTime.of(2024, 3, 15, 10, 30);
ZonedDateTime tokyo = local.atZone(ZoneId.of("Asia/Tokyo"));

.atZone() attaches a time zone to an existing local date-time, producing a ZonedDateTime.

Convert time between zones:

ZonedDateTime newYork = tokyo.withZoneSameInstant(ZoneId.of("America/New_York"));

After executing the above code, newYork contains the same instant as tokyo but in New York's time zone:

2024-03-15T10:30-04:00[America/New_York]
// Example output

To format a ZonedDateTime, use DateTimeFormatter. The pattern letter Z or xxx formats the UTC offset (e.g. +09:00), and VV formats the zone ID (e.g. Asia/Tokyo):

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm xxx");
String formatted = tokyo.format(formatter);
// Example: 2024-03-15 10:30 +09:00

Challenge

Easy

Create a method named convertTime that takes four arguments:

A String (dateTimeStr) in format "yyyy-MM-dd HH:mm"
A String (sourceZone) source time zone ID
A String (targetZone) target time zone ID
A boolean (showOffset) whether to include timezone offset in output

The method should:

Parse the input datetime in the source timezone
Convert it to the target timezone
Return formatted information about both times

Return messages should be:

If invalid datetime: return "Invalid datetime format"
If invalid zone: return "Invalid time zone"
If showOffset is true: include offset in output
Format: "Source: [time1], Target: [time2]"

Cheat sheet

ZonedDateTime represents a date and time with a time zone, useful for working with different time zones.

Create a time in a specific zone:

ZonedDateTime tokyo = ZonedDateTime.now(ZoneId.of("Asia/Tokyo"));

Convert a LocalDateTime to a ZonedDateTime using .atZone():

LocalDateTime local = LocalDateTime.now();
ZonedDateTime zoned = local.atZone(ZoneId.of("Asia/Tokyo"));

Convert time between zones:

ZonedDateTime newYork = tokyo.withZoneSameInstant(ZoneId.of("America/New_York"));

Format a ZonedDateTime including the UTC offset using Z or xxx patterns:

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm xxx");
String formatted = zoned.format(formatter);
// Example: 2024-03-15 10:30 +09:00

Try it yourself

import java.util.Scanner;
import java.time.*;
import java.time.format.*;

public class Main {
    public static String convertTime(String dateTimeStr, String sourceZone, 
                                   String targetZone, boolean showOffset) {
        // Write your code here
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String dateTimeStr = scanner.nextLine();
        String sourceZone = scanner.nextLine();
        String targetZone = scanner.nextLine();
        boolean showOffset = Boolean.parseBoolean(scanner.nextLine());
        
        System.out.println(convertTime(dateTimeStr, sourceZone, targetZone, showOffset));
    }
}