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
   

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2. java.util.Date
   

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3. java.util.Date
   Date is not a date
   

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4. java.util.Date
   Date is not a date
   

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5. java.util.Date
   Date is not a date
   A Date in an instance in Time
   

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6. java.util.Date
   Date is not a date
   A Date in an instance in Time
   Date = Date + Time
   

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7. java.util.Date
   val date = Date(2021, 1, 19)
   

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8. java.util.Date
   val date = Date(2021, 1, 19)
   Is this January 19, 2021?
   

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9. java.util.Date
   val date = Date(2021, 1, 19)
   Is this January 19, 2021? - No
   

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10. java.util.Date
    val date = Date(2021, 1, 19)
    Is this January 19, 2021? - No
    Year is 1900-based offset
    

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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
    

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12. java.util.Date
    val date = Date(2021, 1, 19)
    It is February 19, 3921
    

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13. java.util.Date
    val date = Date(2020, 0, 35)
    print(date.toString())
    

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14. java.util.Date
    val date = Date(2020, 0, 35)
    print(date.toString())
    Expected - Exception. What is even January 35?
    

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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
    

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16. java.util.Date
    val date = Date(2021, 1, 19)
    val day = date.day
    

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17. java.util.Date
    val date = Date(2021, 1, 19)
    val day = date.day
    Expected: 19
    

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18. java.util.Date
    val date = Date(2021, 1, 19)
    val day = date.day
    Expected: 19
    Actual: 3
    

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19. Calendar
    

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20. Calendar
    • Cannot format Calendar instance directly
    

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21. Calendar
    • Cannot format Calendar instance directly
    • Mutable
    

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22. Calendar
    • Cannot format Calendar instance directly
    • Mutable
    • Still no arithmetic functions
    

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23. Joda-Time
    

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24. Joda-Time
    • De-facto solution before Java 8
    

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25. Joda-Time
    • De-facto solution before Java 8
    • Separate classes for each concept
    

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26. Joda-Time
    • De-facto solution before Java 8
    • Separate classes for each concept
    • Immutable
    

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27. Joda-Time
    • De-facto solution before Java 8
    • Separate classes for each concept
    • Immutable
    • Handy classes for arithmetic operations
    

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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
    

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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
    

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30. Joda-Time Android
    https://github.com/dlew/joda-time-android
    

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31. Joda-Time Android
    • Joda-Time JAR ships with the TimeZone database
    https://github.com/dlew/joda-time-android
    

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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
    

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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
    

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34. Joda-Time Android - a caution
    https://github.com/dlew/joda-time-android
    

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35. https://github.com/dlew/joda-time-android
    • Loading the TZ data at app startup can be time consuming
    Joda-Time Android - a caution
    

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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
    

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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
    

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38. https://blog.joda.org/2009/11/why-jsr-310-isn-joda-time_4941.html
    Why anything more?
    

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39. https://blog.joda.org/2009/11/why-jsr-310-isn-joda-time_4941.html
    • Joda-Time has some design flaws
    Why anything more?
    

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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?
    

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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?
    

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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?
    

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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?
    

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44. java.time
    

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45. java.time
    • Introduced in Java 8
    

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46. java.time
    • Introduced in Java 8
    • But available only on API Level 26+
    

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47. java.time
    • Introduced in Java 8
    • But available only on API Level 26+
    • Results in ClassNotFoundException before API Level 25
    

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48. ThreeTenBP
    • Backport of java.time library to be used on Java 6 and 7
    

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49. ThreeTenBP
    • Backport of java.time library to be used on Java 6 and 7
    • Ships TZ data along with the JAR
    

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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
    

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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
    

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52. Syntactic Sugar
    val array = arrayOf(3, 5, 6)
    array[1]
    val list = listOf(3, 5,6 )
    list[1]
    

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53. Desugaring
    

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54. Core Library Desugaring
    

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55. Core Library Desugaring
    • Android Gradle Plugin 3.0.0+ added support for some Java 8 language
    features
    

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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
    

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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
    

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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'
    }
    

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59. ThreeTenABP -> java.time
    • Enable core library desugaring
    • Change all imports from org.threeten.bp to java.time
    • Profit
    

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60. Recap
    • Don't use java.util.Date
    

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61. Recap
    • Don't use java.util.Date
    • If on Joda-Time, no need to migrate
    

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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
    

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63. @iamsubhrajyoti
    

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