Kotlin Everywhere Hamburg: Refactoring Legacy Code with Kotlin and Coroutines

Legacy code can be quite the challenge to manage, often resulting from untested scenarios, quick fixes, or less than successful initiatives. With few developers wanting to deal with it, it can end up with little remaining knowledge of it's inner workings.

We can take many learnings from Michael Feathers book on "Working Effectively with Legacy Code", but we can also use Kotlin migration as an effective tool to leverage the management, reduction, and removal of legacy code in our applications.

In this session, you'll learn how to get started with Kotlin in your projects, tips and tricks on how to preserve your version control history, some pitfalls when migrating from Java, and what new technologies you can make use of in your journey with Kotlin.

Transcript

1. Refactoring Legacy Code with Kotlin & Coroutines Kotlin Everywhere: Hamburg @askashdavies
2. @askashdavies
3. Java @askashdavies
4. { } @askashdavies
5. Streams ↝ @askashdavies
6. @askashdavies
7. Kotlin @askashdavies
8. Null @askashdavies
9. if (foo == null) { bar(); } @askashdavies
10. O"ensive Code < > @askashdavies
11. Urgency @askashdavies
12. Kotlin? @askashdavies
13. Kotlin @askashdavies
14. @askashdavies
15. Google IO 2018 @askashdavies
16. ! " @askashdavies
17. Google IO 2019 @askashdavies
18. Kotlin @askashdavies
19. Libraries @askashdavies
20. @askashdavies
21. @askashdavies
22. @askashdavies
23. @askashdavies
24. @askashdavies
25. @askashdavies
26. Kotlin @askashdavies
27. Idiomacy @askashdavies
28. @askashdavies
29. Idiomatic Code @askashdavies
30. Idiomatic Code • Consistent, easier to read • Less cognitive load • Less ambiguity • Function > Style @askashdavies
31. Code Style • kotlinlang.org/docs/reference/coding-conventions.html • android.github.io/kotlin-guides/style.html @askashdavies
32. Refactoring Legacy Code @askashdavies
33. ⌃⌥⇧K @askashdavies
34. @askashdavies
35. @askashdavies
36. public class BadJavaActivity extends Activity { @Inject Dependency dependency; } @askashdavies
37. General Assumptions @askashdavies
38. class BadKotlinActivity : Activity() { @Inject var dependency: Dependency? = null } @askashdavies
39. class SlightlyLessBadKotlinActivity : Activity() { @Inject internal lateinit var dependency: Dependency } @askashdavies
40. UninitializedPrope.yAccessException! @askashdavies
41. lateinit var file: File if (::file.isInitialized) { /* ... */ } @askashdavies
42. Data Classes @askashdavies
43. public class User { private String firstName; private String lastName; public User(String firstName, String lastName) { this.firstName = firstName; this.lastName = lastName; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } @Override public boolean equals(Object o) { if (this == o) { return true; } if (o == null || getClass() != o.getClass()) { return false; } User user = (User) o; return Objects.equals(firstName, user.firstName) && Objects.equals(lastName, user.lastName); } @Override public int hashCode() { return Objects.hash(firstName, lastName); } } @askashdavies
44. class User(var firstName: String?, var lastName: String?) { override fun equals(o: Any?): Boolean { if (this === o) { return true } if (o == null || javaClass != o.javaClass) { return false } val user = o as User? return firstName == user!!.firstName && lastName == user.lastName } override fun hashCode(): Int { return Objects.hash(firstName, lastName) } } @askashdavies
45. data class User(val firstName: String, val lastName: String) @askashdavies
46. data class User(val firstName: String, val lastName: String? = null) @askashdavies
47. @NotNull public final User copy(@Nullable String firstName, @Nullable String lastName) { return new User(firstName, lastName); } @askashdavies
48. Kotlin • Singleton objects • String interpolation • Elvis operator ! • Destructuring • Extension functions • Scoping functions @askashdavies
49. Maintaining History @askashdavies
50. Maintaining History • Change extension .java -> .kt • First commit • Apply Kotlin conversion • Second commit @askashdavies
51. Maintaining History Refactoring @askashdavies
52. Refactoring @askashdavies
53. Refactoring SOLID • Single-responsibility • Open-closed • Liskov substitution • Interface segregation • Dependency inversion @askashdavies
54. Refactoring Single Responsibility @askashdavies
55. Perspective @askashdavies
56. Asynchronicity @askashdavies
57. Concurrency is Hard @askashdavies
58. Thread new Thread(() -> { foo(); }).start(); @askashdavies
59. CompletableFuture CompletableFuture.supplyAsync(this::findSomeData) .thenApply(this:: intReturningMethod) .thenAccept(this::notify); @askashdavies
60. RxJava Observable .fromIterable(resourceDraft.getResources()) .flatMap(resourceServiceApiClient::createUploadContainer) .zipWith(Observable.fromIterable(resourceDraft.getResources()), Pair::create) .flatMap(uploadResources()) .toList() .toObservable() .flatMapMaybe(resourceCache.getResourceCachedItem()) .defaultIfEmpty(Resource.getDefaultItem()) .flatMap(postResource(resourceId, resourceDraft.getText(), currentUser, resourceDraft.getIntent())) .observeOn(AndroidSchedulers.mainThread()) .subscribeOn(Schedulers.io()) .subscribe( resource -> repository.setResource(resourceId, resource, provisionalResourceId), resourceUploadError(resourceId, resourceDraft, provisionalResourceId) ); @askashdavies
61. @askashdavies
62. What If? @askashdavies
63. Coroutines @askashdavies
64. fun main() { GlobalScope.launch { delay(1000L) println("World!") } println("Hello,") Thread.sleep(2000L) } // Hello, // World! @askashdavies
65. fun main() { GlobalScope.launch { delay(1000L) println("World!") } println("Hello,") Thread.sleep(2000L) } // Hello, // World! @askashdavies
66. fun main() { GlobalScope.launch { delay(1000L) println("World!") } println("Hello,") Thread.sleep(2000L) } // Hello, // World! @askashdavies
67. ⚖ Stability @askashdavies
68. @askashdavies
69. @Annotations ( ! Here be dragons) @askashdavies
70. Annotations @ExperimentalCoroutinesApi // ⚠ @askashdavies
71. Annotations @ExperimentalCoroutinesApi // ⚠ @FlowPreview // ⚠ @askashdavies
72. Annotations @ExperimentalCoroutinesApi // ⚠ @FlowPreview // ⚠ @ObsoleteCoroutinesApi // ⚠ @askashdavies
73. Annotations @ExperimentalCoroutinesApi // ⚠ @FlowPreview // ⚠ @ObsoleteCoroutinesApi // ⚠ @InternalCoroutinesApi // ☠ @askashdavies
74. Annotations @Experimental @askashdavies
75. ! Coroutines @askashdavies
76. ! Native (rst-pa-y library @askashdavies
77. E"cient @askashdavies
78. ! Easy-to-use @askashdavies
79. ! suspend fun @askashdavies
80. ! Suspend fun main() { GlobalScope.launch { delay(1000L) println("World!") } println("Hello,") Thread.sleep(2000L) } // Hello, // World! @askashdavies
81. ! Suspend fun main() { GlobalScope.launch { doWorld() println("Hello,") Thread.sleep(2000L) } } suspend fun doWorld() { delay(1000L) println("World!") } // Hello, // World! @askashdavies
82. ! Suspend fun main() { GlobalScope.launch { doWorld() println("Hello,") Thread.sleep(2000L) } } suspend fun doWorld() { withContext(Dispatchers.IO) { delay(1000L) println("World!") } } // Hello, // World! @askashdavies
83. Dispatchers @askashdavies
84. Dispatchers • Default • IO • Main • Android (Main Thread Dispatcher) • JavaFx (Application Thread Dispatcher) • Swing (Event Dispatcher Thread) • Unconfined @askashdavies
85. Testing @Test fun testFoo() = runBlockingTest { val actual = foo() // ... } suspend fun foo() { delay(1_000) // ... } @askashdavies
86. Fu#her Reading • Google Codelab: Refactoring to Kotlin https://codelabs.developers.google.com/codelabs/java-to-kotlin/ • KotlinX Coroutine Test https://github.com/Kotlin/kotlinx.coroutines/tree/master/kotlinx-coroutines-test • Sean McQuillan: Coroutines + Testing = https://www.droidcon.com/media-detail?video=352671106 • Ash Davies: RxJava & Coroutines: A Practical Analysis v3 https://speakerdeck.com/ashdavies/rxjava-and-coroutines-a-practical-analysis- v3 @askashdavies
87. Thanks! @askashdavies