You can use the ChronoUnit.DAYS enum to calculate the days between two ZonedDateTime instances in Java. It provides the between() method to calculate the amount of time between two temporal objects:

// Create date instances
ZonedDateTime startZonedDateTime = ZonedDateTime.parse("2022-03-23T10:40:30+01:00[Europe/Paris]");
ZonedDateTime endZonedDateTime = ZonedDateTime.parse("2022-11-12T10:40:33+05:00[Asia/Karachi]");

// Calculate the difference
long days = ChronoUnit.DAYS.between(startZonedDateTime, endZonedDateTime);

// Print days
System.out.println("Days between " + startZonedDateTime + " and " + endZonedDateTime + ": " + days);
// Days between 2022-03-23T10:40:30+01:00[Europe/Paris] 
// and 2022-11-12T10:40:33+05:00[Asia/Karachi]: 233

The ChronoUnit enum class was introduced in Java 8 to represent individual date and time units such as day, month, year, week, hour, minutes, etc.

The between() method returns a negative difference in days if the start is after the end date, as shown below:

System.out.println(ChronoUnit.DAYS.between(endZonedDateTime, startZonedDateTime)); // -233

You can also use the ChronoUnit enum to calculate the difference between two ZonedDateTime objects in weeks, months, and years:

System.out.println(ChronoUnit.WEEKS.between(startZonedDateTime, endZonedDateTime)); // 33
System.out.println(ChronoUnit.MONTHS.between(startZonedDateTime, endZonedDateTime)); // 7
System.out.println(ChronoUnit.YEARS.between(startZonedDateTime, endZonedDateTime)); // 0

Read this article to learn more about calculating the difference between two dates in Java.

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