Difference in days between two dates in Java?

Question

I need to find the number of days between two dates: one is from a report and one is the current date. My snippet:

  int age=calculateDiffer         


        

Answer 1

ThreeTen-Extra

The Answer by Vitalii Fedorenko is correct, describing how to perform this calculation in a modern way with java.time classes (Duration & ChronoUnit) built into Java 8 and later (and back-ported to Java 6 & 7 and to Android).

Days

If you are using a number of days routinely in your code, you can replace mere integers with use of a class. The Days class can be found in the ThreeTen-Extra project, an extension of java.time and proving ground for possible future additions to java.time. The Days class provides a type-safe way of representing a number of days in your application. The class includes convenient constants for ZERO and ONE.

Given the old outmoded java.util.Date objects in the Question, first convert them to modern java.time.Instant objects. The old date-time classes have newly added methods to facilitate conversion to java.time, such a java.util.Date::toInstant.

Instant start = utilDateStart.toInstant(); // Inclusive.
Instant stop = utilDateStop.toInstant();  // Exclusive.

Pass both Instant objects to factory method for org.threeten.extra.Days.

In the current implementation (2016-06) this is a wrapper calling java.time.temporal.ChronoUnit.DAYS.between, read the ChronoUnit class doc for details. To be clear: all uppercase DAYS is in the enum ChronoUnit while initial-cap Days is a class from ThreeTen-Extra.

Days days = Days.between( start , stop );

You can pass these Days objects around your own code. You can serialize to a String in the standard ISO 8601 format by calling toString. This format of PnD uses a P to mark the beginning and D means “days”, with a number of days in between. Both java.time classes and ThreeTen-Extra use these standard formats by default when generating and parsing Strings representing date-time values.

String output = days.toString();

P3D

Days days = Days.parse( "P3D" );