Modern Date/Time APIs on Android

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Modern Date/Time APIs on Android Droidcon Bucharest 2016 Alex Florescu @ﬂor3scu YPlan

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Overview • Why • Joda time and JSR-310 • What can you do with them • Setup & testing • Good and bad

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Date and Time is hard • Timezones • Daylight savings • Different calendar systems • Leap days/seconds/etc • AND MORE

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Quiz: Leap years • A leap year (e.g. 2016) adds a day, February 29th • What years are leap years?

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Quiz: What is a leap year? • Divisible by four

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Quiz: What is a leap year? • Divisible by four • But NOT divisible by 100

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Quiz: What is a leap year? • Divisible by four • But NOT divisible by 100 • UNLESS divisible by 400

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What’s wrong with Java 6 Date?

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java.util.Date Date someDate = new Date(1967, 5, 10);  System.out.println(someDate); // What date is this? May 10th 1967  June 11th 1967  October 5th 1967  November 6th 1967

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java.util.Date Date someDate = new Date(1967, 5, 10);  System.out.println(someDate); Answer: June 10th 3867 Year: years from 1900  Month: 0-indexed  Day: 1-indexed

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Java 6 Date/Time API • Mutable • 0-indexed months • Little support for simple operations • No representation for duration, non-time-zone dates, only dates, only times etc.

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JVM Alternatives • Joda Time • Since 2004 • De-facto date/time solution pre-Java 8 • JSR-310 / Java 8 API • Released in 2014 • Same project lead as Joda Time • Ofﬁcial API for Java 8, backported to Java 6

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Joda time • Still actively maintained • For new projects use Java 8 API • See comparison and Stephen Colebourne’s blog

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Joda time on Android • Can use directly, but large memory footprint • See problem description • Solution: https://github.com/dlew/joda-time-android • Method count: 5053

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JSR-310 / Java 8 API • Ofﬁcial JVM solution (>= Java 8) • Built with experience from Joda time • Generally better performance • Smaller package, fewer methods

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ThreeTen on Android • Backport library “ThreeTen”, Java 6 compatible • Same problem as Joda if use JVM lib directly • Use: https://github.com/JakeWharton/ThreeTenABP • Method count: 3278

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Setup • In build.gradle: compile 'com.jakewharton.threetenabp:threetenabp:1.0.3' • In Application.onCreate(): @Override public void onCreate() { super.onCreate(); AndroidThreeTen.init(this); }

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Cool things ZonedDateTime.now(); //2016-03-12T12:11:25.371+02:00  [Europe/Bucharest] ZonedDateTime.now(ZoneId.of("Europe/ London"));   //2016-03-12T10:11:26.374+00:00  [Europe/London]

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Cool things LocalDateTime now = LocalDateTime.now(); LocalDate tomorrowDay = now.toLocalDate().plusDays(1); LocalDateTime noonTomorrow = tomorrowDay.atTime(12, 0);

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Cool things LocalTime now = LocalTime.now(); LocalTime lunchTime =   LocalTime.of(12, 30);   if (now.isAfter(lunchTime)) {  // GO TO LUNCH  }

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Testing • UI tests — just test the app • Robolectric tests — initialise with Robo context • Plain JUnit tests — use JVM back port  testCompile 'org.threeten:threetenbp: 1.3.1'

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Testing • Note: Can’t mix Robolectric and plain JUnit tests • Separate plain JUnit and Robolectric tests • If using ThreeTenABP in a module/conﬁguration, all tests (that involve ThreeTen) must be Robolectric

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Why should you use? • Safer, clearer, ﬂuent API • Easier to do everything • Immutable • Excellent timezone support

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Any negatives? • Immutable (Android GC’ing is not JVM GC’ing) • 5% towards DEX limit • Need to connect old and new APIs • Android speciﬁc locale issues (e.g. 24-hr toggle)