Unexpected value setting java calendar minutes

Question

I am trying to create a time interval, as the starting point is the current time and the minimum and maximum values are calculated by a special variable which is set by the user (upperBound). So the code looks like:

private static int upperBound = 1440;
.....
Calendar calendar = Calendar.getInstance();
System.out.println("Now:\t\t\t" + calendar.getTime());
calendar.set(Calendar.MINUTE, -upperBound);
System.out.println("After the change:\t" + calendar.getTime());

and the output is:

Now:            Mon Jan 27 14:53:42 EET 2014
After the change:   Sun Jan 26 14:00:42 EET 2014

But I expect to be (after the change): Sun Jan 26 14:53:42 EET 2014

What is wrong here?

Answer 1

You should use add() method, not set

calendar.add(Calendar.MINUTE, -upperBound);

Answer 2

tl;dr

Instant.now()
       .plus( 1440 , ChronoUnit.MINUTES )

Details

The modern way is with the java.time classes that supplant the troublesome old legacy Calendar class.

Using java.time

The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).

Instant instant = Instant.now();

You can add amounts of time to that.

Instant later = instant.plus( 24 , ChronoUnit.HOURS ) ;

If you mean to add specifically minutes, so be it.

Instant later = instant.plus( 1440 , ChronoUnit.MINUTES );

If you want to add a day in calendar terms, to account for anomalies such as Daylight Saving Time (DST), you must apply a time zone.

ZoneId z = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt = instant.atZone( z );
ZonedDateTime zdtLater = zdt.plusDays( 1 );

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About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

Where to obtain the java.time classes?

• Java SE 8 and SE 9 and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
  • See How to use ThreeTenABP….

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.