CODEWITHSUNDEEP
javatimezonejodatime
Leo Aso
Leo Aso

Reputation: 12463

Joda-Time DateTimeZone not comparing correctly

I've been working on unit tests for a project that uses Joda-Time, and I noticed that DateTimeZone instances that should represent the same time-zone aren't returning true on equals. In particular, on unit tests like these below

// should be the same
DateTimeZone WAT = DateTimeZone.forOffsetHours(1); // GMT+01:00
DateTimeZone LAG = DateTimeZone.forID("Africa/Lagos"); // Lagos

DateTime sample = new DateTime(2017, 11, 15, 10, 50);
DateTime dtzWAT = sample.withZoneRetainFields(WAT);
DateTime dtzLAG = sample.withZoneRetainFields(LAG);

@Test public void compareZones() { assertEquals(WAT, LAG); }
@Test public void compareTimes() { assertEquals(dtzWAT, dtzLAG); }

both tests fail even though Africa/Lagos and GMT+01:00 are the same time zone, and the two DateTimes represent the same instant - in fact, the two tests below confirm this

// both succeed
@Test public void compareStrings() {
    assertEquals(dtzWAT.toString(), dtzLAG.toString()); 
}

@Test public void checkSameTime() { 
    assertFalse(dtzLAG.isBefore(dtzWAT)); 
    assertFalse(dtzWAT.isBefore(dtzLAG)); 
}

Why does this happen? Why are the two time-zone instances not equivalent, and is there anyway around this? Any help would be appreciated.

Upvotes: 1

Views: 359

Answers (1)

Andy Turner
Andy Turner

Reputation: 140299

why does this happen

The DateTimeZones are not equal: one is called Africa/Lagos, the other is GMT+01:00. It says in the Javadoc of DateTimeZone.equals

true if equal, based on the ID and all internal rules

And for DateTime.equals:

Compares this object with the specified object for equality based on the millisecond instant, chronology and time zone.

The time zones aren't equal, so the DateTimes aren't equal.

Maybe they are effectively equal, doesn't mean they actually are.

Note that java.util.TimeZone has the hasSameRules(...) method, which is a separate notion from equality.

Upvotes: 2

Related Questions