Date difference using Java

Question

I have two date periods in my invoice,

Total bill period - 6 Nov 2019 to 3 Feb 2020 (String)

price change period - 22 Jan 2020 to 3 Feb 2020 (String)

So the total bill period is for 90 days, in which there is a price change for 13 days from 22nd Jan 2020 to 3 Feb 2020.

I need to get the bill period for the non price change days which is - 6 Nov 2019 to 21 Jan 2020.

What is the best way to get the difference between these dates ?

Thanks in advance!

It is unclear what your data is. Do you have the dates as strings in exactly the given format? Is there only ever one price change period per bill period? — Felix Dombek, Mar 10 '20 at 00:13
You probably want [Period.between](https://docs.oracle.com/en/java/javase/13/docs/api/java.base/java/time/Period.html#between%28java.time.LocalDate,java.time.LocalDate%29). — VGR, Mar 10 '20 at 00:38
@VGR Or for *the total bill period is for 90 days* perhaps `ChronoUnit.DAYS.between()`. In any case it’s all in the answers to the linked original question. — Ole V.V., Mar 10 '20 at 04:19

score -1 · Answer 1 · answered Mar 10 '20 at 00:42

Assuming the assumptions in my comment hold, and you have strings like this:

String billPeriodStart   = "6 Nov 2019";
String billPeriodEnd     = "3 Feb 2020";
String changePeriodStart = "22 Jan 2020";
String changePeriodEnd   = "3 Feb 2020";

Something like this might work (untested):

SimpleDateFormat dateFormat = new SimpleDateFormat("dd MMM yyyy");
Date billPeriodStartDate = dateFormat.parse(billPeriodStart);
// same for the other values

Calendar cal = Calendar.getInstance();

cal.setDate(changePeriodStartDate);
cal.add(Calendar.DAY, -1);
Date dateBeforeChangePeriod = cal.getTime();

cal.setDate(changePeriodEndDate);
cal.add(Calendar.DAY, 1);
Date dateAfterChangePeriod = cal.getTime();

boolean hasDaysBeforeChangePeriod = !dateBeforeChangePeriod.before(billPeriodStartDate);
boolean hasDaysAfterChangePeriod  = !dateAfterChangePeriod.after(billPeriodEndDate);

if (hasDaysBeforeChangePeriod) {
  // print billPeriodStartDate to dateBeforeChangePeriod 
}
if (hasDaysAfterChangePeriod) {
  // print dateAfterChangePeriod to billPeriodEndDate
}
if (!hasDaysBeforeChangePeriod && !hasDaysAfterChangePeriod) {
  // print "none"
}

Please don’t teach the young ones to use the long outdated and notoriously troublesome `SimpleDateFormat` class. At least not as the first option. And not without any reservation. Today we have so much better in [`java.time`, the modern Java date and time API,](https://docs.oracle.com/javase/tutorial/datetime/) and its `DateTimeFormatter`. — Ole V.V., Mar 10 '20 at 04:02

Date difference using Java

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