Travelling across Asia - Our journey from Java to Kotlin

Kotlin has established itself in the Android development community since v1.0 last year, and with official support announced at I/O this year, it’s an exciting time to get started with this language in your work.

This talk will take you through Deliveroo’s journey from a full Java codebase to using Kotlin across the project. Learn how to get your colleagues involved and convert them to Kotlin supporters. You will also learn how they got started, the problems they ran into and how Kotlin can improve your codebase, your app and your sanity.

Transcript

1. TRAVELLING ACROSS ASIA OUR JOURNEY FROM JAVA TO KOTLIN Amal Kakaiya @K4KYA Maria Neumayer @marianeum
3. DISCLAIMER: COULD TAKE MORE THAN 20 HOURS
5. Java Kotlin AutoValue/Lombok Data classes Streams support Standard lib functions Retrolambda Built in lambda support Butterknife Kotterknife/delegate properties
6. ADOPTING A NEW LANGUAGE IS A HUGE STEP
7. TESTS ARE AN EASY WAY TO GET STARTED
8. TESTS ARE AN EASY WAY TO GET STARTED BUT NOT VERY EXCITING
9. HOW MUCH COULD WE IMPROVE THE MAIN APP?
11. KOTLIN HOUR - GET FAMILIAR WITH THE LANGUAGE
12. YOU CAN’T START USING A LANGUAGE WITHOUT EVERYBODY KNOWING IT
13. DO WE REALLY WANT TO ADD ANOTHER DEPENDENCY?
16. FIND YOUR OWN PACE
18. IT WASN’T A SMOOTH RIDE
19. LEARN FROM EACH OTHER
20. WE REVIEW CODE EVERY DAY
22. ANDROID STUDIO IS YOUR FRIEND
23. private fun mapToIds(items: List<Item>): List<String> { val ids = mutableListOf<String>() for (item in items) { ids.add(item.id) } return ids }
24. private fun mapToIds(items: List<Item>): List<String> { val ids = items.map { it.id } return ids }
25. private fun mapToIds(items: List<Item>): List<String> { return items.map { it.id } }
26. private fun mapToIds(items: List<Item>): List<String> = items.map { it.id }
27. WHAT’S THIS CODE DOING?
28. private final mapToId(Ljava/util/List;)Ljava/ util/List; L0 LINENUMBER 2 L0 ALOAD 1 CHECKCAST java/lang/Iterable ASTORE 2 ———————— 75 more lines ————————
29. private final List mapToId(List items) { Iterable $receiver$iv = (Iterable)items; Collection destination$iv$iv = (Collection)(new ArrayList(CollectionsKt.collectionSizeOrDefault($receiver $iv, 10))); Iterator var5 = $receiver$iv.iterator(); while(var5.hasNext()) { Object item$iv$iv = var5.next(); Item it = (Item)item$iv$iv; String var12 = it.id; destination$iv$iv.add(var12); } return (List)destination$iv$iv; }
30. GETTING STARTED WITH TESTS
31. MOCKS Intent expectedIntent = mock(Intent.class);
32. MOCKS val expectedIntent = mock(Intent::java.class)
33. MOCKS val expectedIntent = mock<Intent>()
34. MOCKS OR val expectedIntent = mock<Intent>() val expectedIntent: Intent = mock()
35. MOCKS @Mock RouteService routeService; MockitoAnnotations.initMocks(this);
36. MOCKS @Mock lateinit var routeService: RouteService MockitoAnnotations.initMocks(this)
37. SIMULATING when(preferences.hasSession()).thenReturn(loggedIn);
38. SIMULATING `when`(preferences.hasSession()).thenReturn(loggedIn)
39. SIMULATING whenever(preferences.hasSession()).thenReturn(loggedIn)
40. VERIFY WITH CAPTORS verify(screen).updateScreen(captor.capture()); ScreenUpdate update = captor.getValue();
41. VERIFY WITH CAPTORS verify(screen).updateScreen(capture(captor)) val update = captor.value
42. VERIFY WITH CAPTORS @Captor lateinit var captor: KArgumentCaptor<ScreenUpdate>
43. VERIFY WITH CAPTORS @Captor lateinit var captor: KArgumentCaptor<ScreenUpdate> verify(screen).updateScreen(captor.capture()) val update = captor.lastValue
44. VERIFY WITH CAPTORS TOTALLY SHOULD HAVE BEEN ARGUMENTKAPTOR… JUS’ SAYIN’ @Captor lateinit var captor: KArgumentCaptor<ScreenUpdate> verify(screen).updateScreen(captor.capture()) val update = captor.lastValue
45. MOCKS AND NULLABLE /** Matches any object, excluding nulls. */ inline fun <reified T : Any> any() = Mockito.any(T::class.java) ?: createInstance<T>() /** Matches anything, including nulls. */ inline fun <reified T : Any> anyOrNull(): T = Mockito.any<T>() ?: createInstance<T>()
46. CONVERTING CODE
47. CONVERTING CODE ⌘⌥⇧K Ctrl+Alt+⇧+K
48. CONVERTING CODE
49. CONVERTING CODE
50. CONVERSION CREEP
51. NULLPOINTEREXCEPTION
52. KOTLINNULLPOINTEREXCEPTION
53. CONSIDER NULLABILITY WHEN IMPLEMENTING A JAVA INTERFACE private val passwordActionListener = TextView.OnEditorActionListener { _: TextView, _: Int, _: KeyEvent -> login(password()) }
54. CONSIDER NULLABILITY WHEN IMPLEMENTING A JAVA INTERFACE private val passwordActionListener = TextView.OnEditorActionListener { _: TextView, _: Int, _: KeyEvent -> login(password()) }
55. CONSIDER NULLABILITY WHEN IMPLEMENTING A JAVA INTERFACE private val passwordActionListener = TextView.OnEditorActionListener { _: TextView, _: Int, _: KeyEvent -> login(password()) }
56. CONSIDER NULLABILITY WHEN IMPLEMENTING A JAVA INTERFACE ! ! ! ! ! ! ! ! private val passwordActionListener = TextView.OnEditorActionListener { _: TextView, _: Int, _: KeyEvent -> login(password()) }
57. CONSIDER NULLABILITY WHEN IMPLEMENTING A JAVA INTERFACE private val passwordActionListener = TextView.OnEditorActionListener { _: TextView, _: Int, _: KeyEvent? -> login(password()) } "
58. CONVERTING CODE class VerifyActivity: BaseActivity<VerifyPresenter>, VerifyScreen { override val message: String = getString(R.string.verify_error)
59. CONVERTING CODE class VerifyActivity: BaseActivity<VerifyPresenter>, VerifyScreen { override val message: String get() = getString(R.string.verify_error)
60. USE VERSION CONTROL EFFECTIVELY AND YOUR TEAM WILL ❤ YOU
61. $ VERSION HISTORY
62. VERSION CONTROL CONVERSION AS ONE COMMIT
63. VERSION CONTROL MERGE CONVERSIONS QUICKLY
64. VERSION CONTROL SHARE WHAT YOU LEARNED
65. SHARE WHAT YOU LEARNED VERSION CONTROL
66. SHARE WHAT YOU LEARNED VERSION CONTROL
67. VERSION CONTROL LEAVE IN RETURN TYPES WHEN IT MAKES SENSE
68. VERSION CONTROL private fun showPrompt(confirmed: Boolean) = zip(flipper().confirmDrinkingAgeEnabled(), just(confirmed) { enabled, confirmed -> enabled && (!confirmed) }
69. VERSION CONTROL private fun showPrompt(confirmed: Boolean): Observable<Boolean> = zip(flipper().confirmDrinkingAgeEnabled(), just(confirmed) { enabled, confirmed -> enabled && (!confirmed) }
70. ANDROIDANNOTATIONS AUTOVALUE BUTTERKNIFE LOMBOK DAGGER CUSTOM ANNOTATION PROCESSOR
71. KAPT KAY - AY - PEE - TEE
72. KAPT VS LOMBOK A TRUE STORY
73. IMMUTABILITY? private Item addNameToItem(Item item, Name other) { ItemBuilder builder = item.toBuilder() builder.name(other.getName()); return builder.build() }
74. IMMUTABILITY? private Item addNameToItem(Item item, Name other) { ItemBuilder builder = item.toBuilder() builder.name(other.getName()); return builder.build() } private fun addNameToItem(item: Item, other: Name): Item { return item.copy(name = other.name) }
75. WHAT WOULD WE CHANGE?
76. DON’T JUST START WITH TESTS
77. CONVERT UTIL CLASSES EARLY
78. @file:JvmName("ViewUtil") @JvmName("showView") fun View.show(visible: Boolean) { visibility = if (visible) VISIBLE else GONE }
79. DO WHAT WORKS FOR YOUR TEAM
82. THANK YOU WE’RE HIRING Amal Kakaiya @K4KYA Maria Neumayer @marianeum
83. LINKS ▸ Christina Lee & Jake Wharton - Kotlin is here, Life is great and everything will be OK: https://youtu.be/fPzxfeDJDzY ▸ Mockito Kotlin: https://github.com/nhaarman/mockito-kotlin ▸ Kotlin Koans: https://kotlinlang.org/docs/tutorials/koans.html