Our Journey from Java to Kotlin-first!

At Mapbox, it took time, sweat and tears, but we finally adopted Kotlin as the main development language for all Android based projects.

In this session, we will talk about all the bumps we ran into along the way, and describe all the reasons that led us to make the decision to move to Kotlin. We will also show the problems and findings that we encountered along the journey of converting the Mapbox Navigation SDK for Android from 0.x Java to 1.0 Kotlin-first. We will illustrate how we replaced Java tooling and coding style guidelines with Kotlin specific ones, and how we took advantage of some language features and constructs to design APIs that are great for both Kotlin and Java. All this in addition to making sure the SDK was ready for prime time i.e. with S.O.L.I.D. architecture, APIs that are hard to misuse, a low crash rate, well tested and performant.

It's been quite a ride. Do you want to know how it went? Join us!

Transcript

1. Our Journey from Java to
   Kotlin-first!
   Pablo Guardiola
   @Guardiola31337
   

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2. Navigation SDK 1.0
   - Kotlin-first
   - Modularized
   - Clean and performant
   APIs that are hard to
   misuse
   

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3. Episode 1.
   Kotlin
   

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4. SDKs
   

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5. SIZE
   

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6. SIZE
   & Number of methods
   Too many field references: max is 65536
   

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8. Show me the
   numbers!!!
   

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9. Kotlin stdlib increased the
   apk size by around 380 KB and
   added around 6K methods
   

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10. Nope.
    

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11. Benefits
    Developer
    - Intuitive
    - Statically typed
    - Type inference
    - Outstanding IDE support
    - Functional and
    object-oriented
    - Expressive
    - Concise
    - null safe
    - //.
    

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12. Client / User
    - More strongly typed
    than Java
    - DSLs
    - Modern, powerful and
    safe
    - Fewer methods, less
    weight
    Benefits
    

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13. Nope.
    

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16. 30.5%
    SDK / Libraries
    

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17. 77%
    Extension
    functions
    

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18. Nope.
    

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21. Nope.
    

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22. Navigation SDK
    

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23. YES
    - Still in Beta (0.x)
    - Young
    - Client apps in Kotlin
    - Excitement
    

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24. All in on Kotlin
    or not?
    Sep 2019
    

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25. NO
    - stdlib adds binary size
    - Kotlin versions
    incompatibility
    - Extra effort to make
    APIs Java friendly
    

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26. YES
    - Google’s preferred
    language for Android
    - Productivity
    - New Java features
    adoption is slow
    - OkHttp (v4.x)
    - Concurrency
    - Hiring
    

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27. Oct 8, 2019
    

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29. Episode 2.
    Conversion
    

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30. Code style
    ktlint
    

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32. @NonNull and @Nullable
    annotations
    Analyze > Infer Nullity//.
    

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33. Convert Java to
    Kotlin
    ⌥⇧⌘K
    

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34. Polish Kotlin code
    

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35. if null else / let Elvis operator
    

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36. if null else / let Elvis operator
    

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37. switch / when
    

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38. switch / when
    

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39. callback
    

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40. callback
    

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41. Utils
    

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42. Special
    attention
    - /!
    - lateinit / lazy
    - @NotNull non-annotated
    parameters
    - @JvmStatic and @get:
    - @throws methods
    - Writing Java in Kotlin
    

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43. MockK
    - relaxed = true
    RETURNS_DEEP_STUBS
    - relaxedUnitFun = true
    - Kotlin idiomatic
    - mockkObject
    - mockkStatic
    

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44. Episode 3.
    1.0
    

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45. Public APIs
    - Don’t expose Kotlin
    types
    - Great for both Java and
    Kotlin
    - Java and Kotlin
    examples
    - Master @Jvm annotations
    - Rest of the code
    internal
    

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46. To be continued//.
    

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47. Takeaways
    - El que la sigue la
    consigue (Keep
    insisting)
    - Baby steps
    - Test harness
    - Watch out null checks
    - Designing Good APIs is
    hard
    

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48. Thanks.
    

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49. Questions?
    Pablo Guardiola
    @Guardiola31337
    

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50. Sources
    https://realm.io/realm-report/2017-q4/
    https://pusher.com/state-of-kotlin
    https://developer.squareup.com/blog/okio-2
    https://mockk.io/
    

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