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
2. Navigation SDK 1.0 - Kotlin-first - Modularized - Clean and performant APIs that are hard to misuse
3. Episode 1. Kotlin
4. SDKs
5. SIZE
6. SIZE & Number of methods Too many field references: max is 65536
8. Show me the numbers!!!
9. Kotlin stdlib increased the apk size by around 380 KB and added around 6K methods
10. Nope.
11. Benefits Developer - Intuitive - Statically typed - Type inference - Outstanding IDE support - Functional and object-oriented - Expressive - Concise - null safe - //.
12. Client / User - More strongly typed than Java - DSLs - Modern, powerful and safe - Fewer methods, less weight Benefits
13. Nope.
16. 30.5% SDK / Libraries
17. 77% Extension functions
18. Nope.
21. Nope.
22. Navigation SDK
23. YES - Still in Beta (0.x) - Young - Client apps in Kotlin - Excitement
24. All in on Kotlin or not? Sep 2019
25. NO - stdlib adds binary size - Kotlin versions incompatibility - Extra effort to make APIs Java friendly
26. YES - Google’s preferred language for Android - Productivity - New Java features adoption is slow - OkHttp (v4.x) - Concurrency - Hiring
27. Oct 8, 2019
29. Episode 2. Conversion
30. Code style ktlint
32. @NonNull and @Nullable annotations Analyze > Infer Nullity//.
33. Convert Java to Kotlin ⌥⇧⌘K
34. Polish Kotlin code
35. if null else / let Elvis operator
36. if null else / let Elvis operator
37. switch / when
38. switch / when
39. callback
40. callback
41. Utils
42. Special attention - /! - lateinit / lazy - @NotNull non-annotated parameters - @JvmStatic and @get: - @throws methods - Writing Java in Kotlin
43. MockK - relaxed = true RETURNS_DEEP_STUBS - relaxedUnitFun = true - Kotlin idiomatic - mockkObject - mockkStatic
44. Episode 3. 1.0
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
46. To be continued//.
47. Takeaways - El que la sigue la consigue (Keep insisting) - Baby steps - Test harness - Watch out null checks - Designing Good APIs is hard
48. Thanks.
49. Questions? Pablo Guardiola @Guardiola31337
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/