Comparing two Calendar objects

Question

I want to compare two Calendar objects to see if they both contain the same date. I don\'t care about any value below days.

I\'ve implemented this and I can\'t think

Answer 1

tl;dr

( ( GregorianCalendar ) c1 )
.toZonedDateTime()
.toLocalDate()
.isEqual( 
    ( ( GregorianCalendar ) c2 )
    .toZonedDateTime()
    .toLocalDate()
)

java.time

The Answer by Jon Skeet is correct. But its suggestion to use Joda-Time is outmoded.

The date-time classes bundled with the earliest versions of Java were simply terrible. For example, Date & Calendar and its usual concrete class GregorianCalendar. The adoption of JSR 310 years supplanted those classes with the modern java.time classes. JSR 310 was led by the man who invented Joda-Time, Stephen Colebourne.

Calendar ➙ GregorianCalendar ➙ ZonedDateTime ➙ LocalDate

If given a Calendar convert to ZonedDateTime via GregorianCalendar.

if( myCal instanceOf GregorianCalendar ) {
    GregorianCalendar gc = ( GregorianCalendar ) myCal ; 
}

Then convert to its replacement, ZonedDateTime.

ZonedDateTime zdt = gc.toZonedDateTime() ;

Both GregorianCalendar & ZonedDateTime represent a moment, a specific point on the timeline. That moment viewed through two different time zones such as Tokyo Japan versus Toledo Ohio US could land on two different dates.

To represent a date-only, without time-of-day, and without time zone or offset-from-UTC, use LocalDate class.

LocalDate ld = zdt.toLocalDate() ;

You can compare a pair of LocalDate objects.

boolean isBefore = localDateX.isEqual( localDateY ) ;

You may want to adjust both ZonedDateTime objects to the same time zone before considering their date.

ZoneId zNewYork = ZoneId.of( "America/New_York" ) ;
ZonedDateTime zdtXNewYork = zdtX.withZoneSameInstant( zNewYork ) ;
LocalDate localDateX = zdtXNewYork.toLocalDate() ;

---

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.

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

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

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, Java SE 10, Java SE 11, and later - Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). 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.