Calculate duration until some date

Question

I use this code to generate time until some date:

 String dateStop = "25/11/17 09:00:00";

    // Custom date format
    SimpleDateFormat format = new SimpleDateFormat("yy/MM/dd HH:mm:ss");

    LocalDateTime d1 = LocalDateTime.now();
    Date d2 = null;
    try
    {
        d2 = format.parse(dateStop);
    }
    catch (ParseException e)
    {
        e.printStackTrace();
    }

    // Get msec from each, and subtract.
    long diff = d2.getTime() - d1.getTime();

    long days = TimeUnit.MILLISECONDS.toDays(diff);
    long remainingHoursInMillis = diff - TimeUnit.DAYS.toMillis(days);
    long hours = TimeUnit.MILLISECONDS.toHours(remainingHoursInMillis);
    long remainingMinutesInMillis = remainingHoursInMillis - TimeUnit.HOURS.toMillis(hours);
    long minutes = TimeUnit.MILLISECONDS.toMinutes(remainingMinutesInMillis);
    long remainingSecondsInMillis = remainingMinutesInMillis - TimeUnit.MINUTES.toMillis(minutes);
    long seconds = TimeUnit.MILLISECONDS.toSeconds(remainingSecondsInMillis);

    System.out.println("Days: " + days + ", hours: " + hours + ", minutes: " + minutes + ", seconds: " + seconds);

How I can get the same result but with much more less code?

Try figuring out how to convert the long 'diff' into another representation of time that meets your use case, instead of trying it manually. — Vivek Chavda
– Vivek Chavda, Commented Aug 7, 2017 at 21:49
you don't have getTime() for LocalDateTime, your code is not working — azro
– azro, Commented Aug 7, 2017 at 21:49

azro · Accepted Answer · 2017-08-07 21:59:39Z

You do not need to use Date, parse, Exception, .... You only need LocalDateTime :

LocalDateTime d1 = LocalDateTime.now();
LocalDateTime d2 = LocalDateTime.parse("25/11/17 09:00:00", DateTimeFormatter.ofPattern("yy/MM/dd HH:mm:ss"));

long days = d1.until(d2, ChronoUnit.DAYS);
d1 = d1.plusDays(days);
long hours = d1.until(d2, ChronoUnit.HOURS);
d1 = d1.plusHours(hours);
long minutes = d1.until(d2, ChronoUnit.MINUTES);
d1 = d1.plusMinutes(minutes);
long seconds = d1.until(d2, ChronoUnit.SECONDS);

System.out.println(days + " days " + hours + " hours " + minutes + " minutes " + 
                                                         seconds + " seconds.");

Step by step, from large precision to small, it will look the difference with this precision and then add it to be nearer of the target

Stingy · Accepted Answer · 2017-08-08 21:57:33Z

Inspired by azro's answer, I was motivated to squeeze every bit of code duplication out of it. This resulted in a design that is, ironically, even more verbose, but on the other hand allows for great flexibility in case you want to change the temporal units of the output (e.g., don't display seconds) or the type of the Temporals themselves (e.g. from LocalDateTime to ZonedDateTime):

public static <T extends Temporal> Map<TemporalUnit, Long> temporalDifference(T referenceTemporal, T otherTemporal, TemporalUnit... temporalUnits) {
    SortedSet<TemporalUnit> temporalUnitsSorted
            = Arrays
            .stream(temporalUnits)
            .collect(Collectors.toCollection(()
                    -> new TreeSet<>(
                            Comparator
                            .comparing(TemporalUnit::getDuration)
                            .reversed())));


    Map<TemporalUnit, Long> temporalUnitAmounts = new LinkedHashMap<>();
    T tempTemporal = referenceTemporal;
    for (TemporalUnit temporalUnit : temporalUnitsSorted) {
        long amountForThisUnit = temporalUnit.between(tempTemporal, otherTemporal);
        temporalUnitAmounts.put(temporalUnit, amountForThisUnit);
        tempTemporal.plus(amountForThisUnit, temporalUnit);
    }

    return temporalUnitAmounts;
}

And you can invoke it like this:

LocalDateTime d1 = LocalDateTime.now();
LocalDateTime d2 = LocalDateTime.parse("25/11/17 09:00:00", DateTimeFormatter.ofPattern("yy/MM/dd HH:mm:ss"));

Map<TemporalUnit, Long> temporalUnitAmounts
        = temporalDifference(
                d1,
                d2,
                ChronoUnit.DAYS,
                ChronoUnit.HOURS,
                ChronoUnit.MINUTES,
                ChronoUnit.SECONDS);

System.out.println("Days: " + temporalUnitAmounts.get(ChronoUnit.DAYS)
        + ", hours: " + temporalUnitAmounts.get(ChronoUnit.HOURS)
        + ", minutes: " + temporalUnitAmounts.get(ChronoUnit.MINUTES)
        + ", seconds: " + temporalUnitAmounts.get(ChronoUnit.SECONDS));

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