Time difference calculation bug

SHARPE, Stuart (Commercial & Institutional CDIO) Stuart.SHARPE at natwestmarkets.com
Wed May 3 16:54:53 UTC 2023


I believe I have discovered a bug in java.time. I've searched Jira and couldn't find any existing similar issue.

Consider the following code:

    var t1 = Instant.parse("2023-05-03T10:00:00.000999Z");

    var t2 = Instant.parse("2023-05-03T10:00:01.000Z");

    var t3 = Instant.parse("2023-05-03T10:00:01.001Z");

    System.out.println(MILLIS.between(t1, t2));

    System.out.println(MILLIS.between(t1, t3));

This prints:



Given that t3 is exactly one millisecond later than t2, it does not seem reasonable that they can both be 1000 milliseconds later than t1.

The JavaDoc for between() states "The calculation returns a whole number, representing the number of complete units between the two temporals."

Assuming I have understood this correctly, I think MILLIS.between(t1, t3) is correct but MILLIS.between(t1, t2) should return 999.


Stuart Sharpe

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