The difference between 2 Instants in Calendar Days

Question

So I'm trying to get a specific number with my code. Right now I have:

Instant Today = 2018-07-17T13:45:00Z
Instant Expiration1 = 2018-07-18T11:00:00Z
long daysTilExp = Today.until(Expiration, Chronounit.DAYS)

The problem is that because this isn't exactly 24 hours apart it ends up returning daysTilExp = 0 but I want daysTilExp = 1 I'm trying to get that actual days apart the two Instants are so then even If I change the value of Expiration like so:

Instant Expiration1 = 2018-07-18T06:00:00Z

and now daysTilExp = 2. I looked at some other answers on StackOverflow but it doesn't look like people are using Instant and they aren't wanting the difference the same way

@DominikSandjaja No I want the result to be `2` It would return a `1` as the real answer — TOTOROCATBUS, Jul 17 '18 at 19:04
Please, post the code which compiles. You cant parse `2018-07-17T13:45:00Z` directly to `Instant`, it's not even the String, how is it supposed to work? Use the camelCase with the lower-cased first letter as a variable name. Isn't `Chronounit` supposed to be `ChronoUnit`? — Nikolas Charalambidis, Jul 17 '18 at 19:22
Please explain how the interval from 1:45 PM on Tuesday to 6 AM the following day constitutes two days. It’s not even one full day. Did you mean to write `2018-07-19`? — VGR, Jul 17 '18 at 21:00
You need to choose a time zone for that. It is never the same calendar date everywhere on Earth. — Ole V.V., Jul 18 '18 at 10:37

score 4 · Accepted Answer · answered Jul 17 '18 at 20:30

4

LocalDate will remove the time part and LocalDate objects comparison will yield the expected result:

LocalDateTime  today = LocalDateTime.parse("2018-07-17T13:45:00");
LocalDateTime  expiration = LocalDateTime.parse("2018-07-18T11:00:00");
LocalDate todayDate = today.toLocalDate();
LocalDate expirationDate = expiration.toLocalDate();
long days = todayDate.until(expirationDate, ChronoUnit.DAYS);
System.out.println(days);

answered Jul 17 '18 at 20:30

Pavel Molchanov

2,299
1
19
24

You can just parse it directly to a localdate but you got me there so thanks. – TOTOROCATBUS Jul 18 '18 at 15:48
@TOTOROCATBUS You can, but only of you want the count in UTC will it give you the correct dates. – Ole V.V. Jul 19 '18 at 07:30
@OleV.V. Yes it does – TOTOROCATBUS Jul 19 '18 at 12:29
LocalDate has a parse method but it accepts 2 parameters: date as string and timezone. – Pavel Molchanov Jul 19 '18 at 18:26
@PavelMolchanov [The Java 9 `LocalDate` documentation](https://docs.oracle.com/javase/9/docs/api/java/time/LocalDate.html) mentions two `parse` methods, but none takes a time zone argument. What did you mean, please? – Ole V.V. Jul 20 '18 at 13:16
You are right. It doesn't take timezone :) I tried to use LocalDate to parse the date with the time part but it wasn't working because parser was not able to parse time part. – Pavel Molchanov Jul 20 '18 at 13:19

gnupinguin · Answer 2 · 2023-08-21T05:06:21.743

4

The best way is using DAYS.between() method from java.time.temporal.ChronoUnit. But this way works only for Java 8+ versions. Example:

Date start = new Date();
Date end = new Date(start.getTime() + 10_000);
long daysCount = DAYS.between(start.toInstant(), end.toInstant());

edited Aug 21 '23 at 05:06

answered Dec 07 '20 at 03:31

gnupinguin

81
4

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Very good suggestion for Java 8+ Also for difference in SECONDS (or other units) between Instants java.time.Instant ! Example: ChronoUnit.SECONDS.between( t0 ,Instant.now()); Minor thing: in your code should read "end.toInstant()" (not toInstance() ) – Diego1974 Oct 06 '21 at 13:55

score 2 · Answer 3 · answered Jul 18 '18 at 14:44

    ZoneId zone = ZoneId.of("America/Chicago");

    Instant today = Instant.parse("2018-07-18T17:15:00Z");
    Instant expiration1 = Instant.parse("2018-07-19T05:00:00Z");

    ZonedDateTime todayInZone = today.atZone(zone);
    ZonedDateTime expirationInZone = expiration1.atZone(zone);
    long daysTilExp = todayInZone.toLocalDate().until(expirationInZone, ChronoUnit.DAYS);
    System.out.format("From %s to %s is %d day/s.%n", 
                      todayInZone, expirationInZone, daysTilExp);

From 2018-07-18T12:15-05:00[America/Chicago] to 2018-07-19T00:00-05:00[America/Chicago] is 1 day/s.

So from July 18 to 19 is 1 day. If you wanted both inclusive in the count, just add 1.

Since it is never the same date everywhere on Earth, counting days is different in different time zones. Try changing the time zone and keeping the same instants:

    ZoneId zone = ZoneId.of("Asia/Tokyo");

This changes the output to

From 2018-07-19T02:15+09:00[Asia/Tokyo] to 2018-07-19T14:00+09:00[Asia/Tokyo] is 0 day/s.

As you can read from the output, this is because it is now already July 19 in Japan, so it os counting from July 19 to 19 and getting 0.

So you need to choose in which time zone you want your count.

score 0 · Answer 4 · answered Jul 17 '18 at 19:41

0

Try this:

long daysTilExp = (long) Math.ceil(now.until(goodTo, ChronoUnit.HOURS) / 24.0);

answered Jul 17 '18 at 19:41

RodolfoTVA

77
9

The difference between 2 Instants in Calendar Days

4 Answers4

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