SimpleDateFormat sometimes wrong hours formatting

Question

I want to convert my timestamp into XXhours:YYminutes string. My approach sometimes works correctly unless it’s obtaining greater values. For example, the

193500000 -> 05hours:45minutes (Wrong, correct is 53hours:45minutes)
60300000 -> 16hours:45minutes (correct)
63900000 -> 17hours:45minutes (correct)
108000000-> 06hours:00minutes (Wrong, correct is 30hours:00minutes)
117000000 -> 08hours:30minutes (Wrong, correct is 32hours:30minutes)

    SimpleDateFormat dateFormat = new SimpleDateFormat("HH'hours' mm'minutes'");
    dateFormat.setTimeZone( TimeZone.getTimeZone( "GMT"));
    String string  = dateFormat.format(totalTime);

You're trying to output durations using a function that outputs dates. That's totally unsupported; Java is right here and you are wrong here. There are only 24 hours in a day so you will never get more than 24 for HH. 193500000 is the third day in 1970, at 05:45 in the morning in the GMT timezone. — Erwin Bolwidt, Jan 15 '18 at 09:31
As an aside, even for correct/supported uses, I recommend you don’t use the long outdated and notoriously troublesome `SimpleDateFormat` class. [`java.time`, the modern Java date and time API,](https://docs.oracle.com/javase/tutorial/datetime/) is so much nicer to work with. And additionally includes a `Duration` class exactly made for your purpose (though unfortunately it doesn’t lend itself that well to formatting). — Ole V.V., Jan 15 '18 at 10:10
There are already a number of answer on Stack Overflow that may help, for example [this one](https://stackoverflow.com/a/36379046/5772882). — Ole V.V., Jan 15 '18 at 10:15
Possible duplicate of [How to convert milliseconds to "hh:mm:ss" format?](https://stackoverflow.com/questions/9027317/how-to-convert-milliseconds-to-hhmmss-format) — Ole V.V., Jan 15 '18 at 10:16
Possible duplicate of [How to format a duration in java? (e.g format H:MM:SS)](https://stackoverflow.com/questions/266825/how-to-format-a-duration-in-java-e-g-format-hmmss) — Ole V.V., Jan 15 '18 at 10:29
Usage: A [*timestamp*](https://en.wikipedia.org/wiki/Timestamp) is defined as a representation of *when* an event happened. Though it may for example be a count of milliseconds since the Epoch of Jan 1, 1970 UTC, I gather that this is not what you’ve got. — Ole V.V., Jan 16 '18 at 10:51

talex · Answer 1 · 2018-01-15T09:45:30.010

2

Unfortunately it is impossible with SimpleDateFormat. "HH" means hour in day. If you date is more than 24 hour it will result modulo 24.

I suggest you to write custom code with new time API.

Here is example:

    Duration duration = Duration.ofMillis(193500000);

    long minutes = duration.toMinutes() % 60;
    long hours = duration.toHours();

    System.out.println("" + hours + "hours:"+minutes+"minutes");

edited Jan 15 '18 at 09:45

answered Jan 15 '18 at 09:32

talex

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For Java 9 and later, see the simplification found in the [answer by Ole V. V.](https://stackoverflow.com/a/48274434/642706) – Basil Bourque Jan 16 '18 at 06:31

score 2 · Answer 2 · answered Jan 15 '18 at 09:38

Carefully read this again: https://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html

The HH is hours in a day, never more than 24 :-)

What you want is probably something like this:

    int msecPerHour = 3600*1000;
    int hours = totalTime/msecPerHour;
    int msecPerMinute = 60*1000;
    int minutes = totalTime/msecPerMinute - hours*60;
    String str = "" + hours + " hours " + minutes + " minutes";

score 2 · Answer 3 · answered Jan 16 '18 at 05:05

The answer by talex is correct that you should use a Duration for this. In Java 9 formatting the Duration has become a bit easier and more straightforward to write and read:

public static String formatDuration(long totalTimeMillis) {
    Duration totalDuration = Duration.ofMillis(totalTimeMillis);
    return String.format(Locale.ENGLISH,
            "%02d hours %02d minutes",
            totalDuration.toHours(),
            totalDuration.toMinutesPart());
}

We no longer need the modulo operation (or similar) for finding the minutes. To demonstrate I called the above method using your time values from the question:

    System.out.println(formatDuration(60300000));
    System.out.println(formatDuration(63900000));
    System.out.println(formatDuration(108000000));
    System.out.println(formatDuration(117000000));
    System.out.println(formatDuration(193500000));

It prints the results you asked for:

16 hours 45 minutes
17 hours 45 minutes
30 hours 00 minutes
32 hours 30 minutes
53 hours 45 minutes

I have put in a space between the number and the unit, I find it more readable that way, you can just remove it if you don’t want it.

The %02d specifier in the format string makes sure you get two digits with a leading zero as necessary as in the question: formatDuration(14700000), for example yields 04 hours 05 minutes.

SimpleDateFormat was meant for formatting a date and/or a time of day, not a duration or elapsed time. I say “was” because that class is now long outdated, and since it was also notoriously troublesome I recommend you never use it again. For formatting a date or hour of day use a DateTimeFormatter from java.time.

score 1 · Accepted Answer · answered Jan 15 '18 at 09:30

1

193500000 -> 05hours:45minutes (Wrong, correct is 53hours:45minutes)
That's because 53 hours = 2 days and 5 hours

60300000 -> 16hours:45minutes (correct)
63900000 -> 17hours:45minutes (correct)

108000000-> 06hours:00minutes (Wrong, correct is 30hours:00minutes)
That's because 30 hours = 1 day and 6 hours

117000000 -> 08hours:30minutes (Wrong, correct is 32hours:30minutes)
That's because 32 hours = 1 day and 8 hours

If you only want to calculate the number of hours from ms:

193500000/(1000*60*60)   = number of hours  
(193500000/(1000*60))%60 = number of remaining minutes

answered Jan 15 '18 at 09:30

MrSmith42

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You are right sir, I've didnt thought of this in that way. Thanks ! – Expiredmind Jan 15 '18 at 09:33
1

The java.time classes are seaside, and make your code more self-documenting. – Basil Bourque Jan 16 '18 at 06:33

score 1 · Answer 5 · answered Jan 01 '21 at 01:27

`SimpleDateFormat` is the wrong class for this requirement

Your requirement is to calculate the duration instead of a date-time. SimpleDateFormat or java.time.format.DateTimeFormatter (part of the modern date-time API) should be used to represent a date/time/date-time i.e. something which represents a point in time instead of a period/duration of time. A thumb rule to remember this is:

Use SimpleDateFormat or java.time.format.DateTimeFormatter for something which you refer with since in English grammar Tense.
Use Period and Duration for something which you refer with for in English grammar Tense.

Check The Difference between Since and For – English grammar

In order to get the duration from milliseconds, you can use java.time.Duration which is modelled on ISO-8601 standards and was introduced with Java-8 as part of JSR-310 implementation. With Java-9 some more convenience methods were introduced.

Demo:

import java.time.Duration;

public class Main {
    public static void main(String[] args) {
        Duration duration = Duration.ofMillis(193500000);
        // Default format
        System.out.println(duration);

        // Custom format
        // ####################################Java-8####################################
        String formattedElapsedTime = String.format("%02d hours %02d minutes", duration.toHours(),
                duration.toMinutes() % 60);
        System.out.println(formattedElapsedTime);
        // ##############################################################################

        // ####################################Java-9####################################
        formattedElapsedTime = String.format("%02d hours %02d minutes", duration.toHours(), duration.toMinutesPart());
        System.out.println(formattedElapsedTime);
        // ##############################################################################
    }
}

Output:

PT53H45M
53 hours 45 minutes
53 hours 45 minutes

Learn about the modern date-time API from Trail: Date Time.

For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7.
If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.

score 0 · Answer 6 · answered Jan 15 '18 at 09:34

It looks like you are trying to convert durations, not date-times. SimpleDateFormat is for formatting date-times into different formats for different Locales.

You might be looking for something like this for converting between durations:

String.format("%d hours, %d minutes", 
    TimeUnit.MILLISECONDS.toHours(millis),
    TimeUnit.MILLISECONDS.toMinutes(millis) - 
    TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(millis))
);

SimpleDateFormat sometimes wrong hours formatting

6 Answers6

SimpleDateFormat is the wrong class for this requirement

`SimpleDateFormat` is the wrong class for this requirement