[java] How do I add one month to current date in Java?

tl;dr

LocalDate::plusMonths

Example:

LocalDate.now( )
         .plusMonths( 1 );

Better to specify time zone.

LocalDate.now( ZoneId.of( "America/Montreal" )
         .plusMonths( 1 );

java.time

The java.time framework is built into Java 8 and later. These classes supplant the old troublesome date-time classes such as java.util.Date, .Calendar, & java.text.SimpleDateFormat. The Joda-Time team also advises migration to java.time.

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

Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport and further adapted to Android in ThreeTenABP.

Date-only

If you want the date-only, use the LocalDate class.

ZoneId z = ZoneId.of( "America/Montreal" );
 LocalDate today = LocalDate.now( z );

today.toString(): 2017-01-23

Add a month.

LocalDate oneMonthLater = today.plusMonths( 1 );

oneMonthLater.toString(): 2017-02-23

Date-time

Perhaps you want a time-of-day along with the date.

First get the current moment in UTC with a resolution of nanoseconds.

Instant instant = Instant.now();

Adding a month means determining dates. And determining dates means applying a time zone. For any given moment, the date varies around the world with a new day dawning earlier to the east. So adjust that Instant into a time zone.

ZoneId zoneId = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt = ZonedDateTime.ofInstant( instant , zoneId );

Now add your month. Let java.time handle Leap month, and the fact that months vary in length.

ZonedDateTime zdtMonthLater = zdt.plusMonths( 1 );

You might want to adjust the time-of-day to the first moment of the day when making this kind of calculation. That first moment is not always 00:00:00.0 so let java.time determine the time-of-day.

ZonedDateTime zdtMonthLaterStartOfDay = zdtMonthLater.toLocalDate().atStartOfDay( zoneId );

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?

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.


Joda-Time

Update: The Joda-Time project is now in maintenance mode. Its team advises migration to the java.time classes. I am leaving this section intact for posterity.

The Joda-Time library offers a method to add months in a smart way.

DateTimeZone timeZone = DateTimeZone.forID( "Europe/Paris" );
DateTime now = DateTime.now( timeZone );
DateTime nextMonth = now.plusMonths( 1 );

You might want to focus on the day by adjust the time-of-day to the first moment of the day.

DateTime nextMonth = now.plusMonths( 1 ).withTimeAtStartOfDay();