I need to know if a date match a periodicity, for example, periodicity is 1 hour, and date that user gives is 13/09/2021 23:00, the inicial that my java code should take is 13/09/2021 00:00 and check how many times have to add 1 hour to get the date 13/09/2021 23:00.

The idea now is made a loop and add 1hour to the date and save in an array, then check if the date is inside the array and the position. Is there any other way?

CodePudding user response：

If I understand your question correctly, you just want to calculate how many hours there are between two dates. For that, it's cleaner to use the built-in java.time classes. You can read the two dates into LocalDateTime objects and calculate the time span between them with ChronoUnit.HOURS:

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy HH:mm");
LocalDateTime start = LocalDateTime.parse("13/09/2021 00:00", formatter);
LocalDateTime end = LocalDateTime.parse("13/09/2021 23:00", formatter);
long hours = ChronoUnit.HOURS.between(start, end);

The result will be 23.

For various other units (minutes for example), there's ChronoUnit.MINUTES. Have a look at the documentation. There are a lot of different units to choose from.

CodePudding user response：

I am adding a couple of minor refinements compared to the correct answer by QBrute.

1. The periodicity can be any amount of time in hours, minutes and seconds.

2. I am taking time zone into account so we also get correct results across summer time transitions (spring forward and fall back) and other time anomalies.

3. If there isn’t a whole number of periodicities, I am rounding up to be sure to have at least enough.

   ZoneId userTimeZone = ZoneId.of("Africa/Dar_es_Salaam");
   
   Duration periodicity = Duration.ofMinutes(5);
   ZonedDateTime userTime = ZonedDateTime.of(2021, 9, 13, 23, 0, 0, 0, userTimeZone);
   ZonedDateTime initialTime = ZonedDateTime.of(2021, 9, 13, 0, 0, 0, 0, userTimeZone);
   
   Duration timeBetween = Duration.between(initialTime, userTime);
   long numberOfPeriodicities = timeBetween.dividedBy(periodicity);
   // Has truncation occurred?
   if (initialTime.plus(periodicity.multipliedBy(numberOfPeriodicities)).isBefore(userTime)) {
       // Need one more periodicity
       numberOfPeriodicities  ;
   }
   
   System.out.println(numberOfPeriodicities);
   

Output is:

276

If you want a periodicity of 7.5 minutes, specify Duration.ofMinutes(7).plusSeconds(30). The Duration.dividedBy(Duration) method that I am using was introduced in Java 9.

Link: Oracle tutorial: Date Time explaining how to use java.time.