Journey Of Time

Transcript

1. Journey Of Time KeepTruckin Subhrajyoti Sen Android Worldwide 2021 N O T A P H Y S I C S T A L K
2. java.util.Date
3. java.util.Date Date is not a date
4. java.util.Date Date is not a date
5. java.util.Date Date is not a date A Date in an instance in Time
6. java.util.Date Date is not a date A Date in an instance in Time Date = Date + Time
7. java.util.Date val date = Date(2021, 1, 19)
8. java.util.Date val date = Date(2021, 1, 19) Is this January 19, 2021?
9. java.util.Date val date = Date(2021, 1, 19) Is this January 19, 2021? - No
10. java.util.Date val date = Date(2021, 1, 19) Is this January 19, 2021? - No Year is 1900-based offset
11. java.util.Date val date = Date(2021, 1, 19) Is this January 19, 2021? - No Year is 1900-based offset January is month Zero
12. java.util.Date val date = Date(2021, 1, 19) It is February 19, 3921
13. java.util.Date val date = Date(2020, 0, 35) print(date.toString())
14. java.util.Date val date = Date(2020, 0, 35) print(date.toString()) Expected - Exception. What is even January 35?
15. java.util.Date val date = Date(2020, 0, 35) print(date.toString()) Expected - Exception. What is even January 35? Actual - Wed Feb 04 00:00:00 IST 3920
16. java.util.Date val date = Date(2021, 1, 19) val day = date.day
17. java.util.Date val date = Date(2021, 1, 19) val day = date.day Expected: 19
18. java.util.Date val date = Date(2021, 1, 19) val day = date.day Expected: 19 Actual: 3
19. Calendar
20. Calendar • Cannot format Calendar instance directly
21. Calendar • Cannot format Calendar instance directly • Mutable
22. Calendar • Cannot format Calendar instance directly • Mutable • Still no arithmetic functions
23. Joda-Time
24. Joda-Time • De-facto solution before Java 8
25. Joda-Time • De-facto solution before Java 8 • Separate classes for each concept
26. Joda-Time • De-facto solution before Java 8 • Separate classes for each concept • Immutable
27. Joda-Time • De-facto solution before Java 8 • Separate classes for each concept • Immutable • Handy classes for arithmetic operations
28. Joda-Time Separate classes for each concept • LocalTime - Time without date • LocalDate - Date without time • Instant - Instance in time • Interval - Interval between two Instants • Duration - Time between Instants in milliseconds
29. Joda-Time Arithmetic operations and immutability val today = DateTime() val aMonthLayer = today.plusMonths(1) val daysBetween = Days.daysBetween(today, aMonthLayer).days val dayOfWeek = today.dayOfWeek val dayOfMonth = today.dayOfMonth
30. Joda-Time Android https://github.com/dlew/joda-time-android
31. Joda-Time Android • Joda-Time JAR ships with the TimeZone database https://github.com/dlew/joda-time-android
32. Joda-Time Android • Joda-Time JAR ships with the TimeZone database • ClassLoader.getResourceAsStream() is used to load the TZ data and is not memory efficient https://github.com/dlew/joda-time-android
33. Joda-Time Android • Joda-Time JAR ships with the TimeZone database • ClassLoader.getResourceAsStream() is used to load the TZ data and is not memory efficient • Joda-Time Android loads the TZ data from resources using AssetManager https://github.com/dlew/joda-time-android
34. Joda-Time Android - a caution https://github.com/dlew/joda-time-android
35. https://github.com/dlew/joda-time-android • Loading the TZ data at app startup can be time consuming Joda-Time Android - a caution
36. https://github.com/dlew/joda-time-android • Loading the TZ data at app startup can be time consuming • This can add 50-200ms to cold boot time for app Joda-Time Android - a caution
37. https://github.com/dlew/joda-time-android • Loading the TZ data at app startup can be time consuming • This can add 50-200ms to cold boot time for apps • If possible, defer initialization till you need it Joda-Time Android - a caution
38. https://blog.joda.org/2009/11/why-jsr-310-isn-joda-time_4941.html Why anything more?
39. https://blog.joda.org/2009/11/why-jsr-310-isn-joda-time_4941.html • Joda-Time has some design flaws Why anything more?
40. https://blog.joda.org/2009/11/why-jsr-310-isn-joda-time_4941.html • Joda-Time has some design flaws • Pluggable Chronology Why anything more?
41. https://blog.joda.org/2009/11/why-jsr-310-isn-joda-time_4941.html • Joda-Time has some design flaws • Pluggable Chronology • Complex internals Why anything more?
42. https://blog.joda.org/2009/11/why-jsr-310-isn-joda-time_4941.html • Joda-Time has some design flaws • Pluggable Chronology • Complex internals • Nullability Why anything more?
43. https://blog.joda.org/2009/11/why-jsr-310-isn-joda-time_4941.html • Joda-Time has some design flaws • Pluggable Chronology • Complex internals • Nullability • Difference between Human and Machine times Why anything more?
44. java.time
45. java.time • Introduced in Java 8
46. java.time • Introduced in Java 8 • But available only on API Level 26+
47. java.time • Introduced in Java 8 • But available only on API Level 26+ • Results in ClassNotFoundException before API Level 25
48. ThreeTenBP • Backport of java.time library to be used on Java 6 and 7
49. ThreeTenBP • Backport of java.time library to be used on Java 6 and 7 • Ships TZ data along with the JAR
50. ThreeTenBP • Backport of java.time library to be used on Java 6 and 7 • Ships TZ data along with the JAR • JakeWharton created ThreeTenABP
51. ThreeTenBP • Backport of java.time library to be used on Java 6 and 7 • Ships TZ data along with the JAR • JakeWharton created ThreeTenABP • Can be used back to API Level 15
52. Syntactic Sugar val array = arrayOf(3, 5, 6) array[1] val list = listOf(3, 5,6 ) list[1]
53. Desugaring
54. Core Library Desugaring
55. Core Library Desugaring • Android Gradle Plugin 3.0.0+ added support for some Java 8 language features
56. Core Library Desugaring • Android Gradle Plugin 3.0.0+ added support for some Java 8 language features • AGP 4.0.0+ added support for desugaring Java 8 language API
57. Core Library Desugaring • Android Gradle Plugin 3.0.0+ added support for some Java 8 language features • AGP 4.0.0+ added support for desugaring Java 8 language API • AGP 4.0.0+ supports a subset of java.time
58. java.time without a min API android { defaultConfig { multiDexEnabled true } compileOptions { // Sets Java compatibility to Java 8 sourceCompatibility JavaVersion.VERSION_1_8 targetCompatibility JavaVersion.VERSION_1_8 } } dependencies { coreLibraryDesugaring 'com.android.tools:desugar_jdk_libs:1.0.9' }
59. ThreeTenABP -> java.time • Enable core library desugaring • Change all imports from org.threeten.bp to java.time • Profit
60. Recap • Don't use java.util.Date
61. Recap • Don't use java.util.Date • If on Joda-Time, no need to migrate
62. Recap • Don't use java.util.Date • If on Joda-Time, no need to migrate • On API 21+ , use java.time using core library desugaring
63. @iamsubhrajyoti