Kotlin Features (GDG Ajah Kotlin Everywhere 2019)

As part of the Kotlin/Everywhere community-led events, aimed at exposing Kotlin as a programming language, this talk was created to explain Kotlin's unique/productivity-boosting features.

In this talk, you will get an overview of the Kotlin programming language - its syntax, and its unique features that helps to boost one's productivity while coding.

Transcript

1. Kotlin Features An overview of its syntax, unique language features and productivity boosters
2. Chizoba Ogbonna (@techietoby) Software Lead, Android at Carbon (formerly Paylater)
3. Variables
4. val var
5. val var
6. val var
7. val name: String var name: String
8. val name: String = “techietoby” var name: String = “techietoby”
9. val (immutable /read-only) var (mutable)
10. val name: String = “techietoby” name = “Chizoba” Val cannot be reassigned
11. val name : String = “techietoby” val name = “techietoby” Type inference
12. val count = 5 println(“Total count: $count”) String Templates
13. lateinit var count: Int count = 5 lateinit
14. var count: Int? = null // success var count: Int = null // error Null safety
15. var name: String = “Chizoba” //This can't be null name = null var pictureUrl: String? = “some url” //You can keep a null here pictureUrl = null var age = 100 //The compiler assumes non-null age = null fun returnLength(notNull: String): Int { return notNull.length } returnLength(name) returnLength(pictureUrl)
16. var name: String = “Chizoba” //This can't be null name = null var pictureUrl: String? = “some url” //You can keep a null here pictureUrl = null var age = 100 //The compiler assumes non-null age = null fun returnLength(notNull: String): Int { return notNull.length } returnLength(name) returnLength(pictureUrl)
17. var name: String = “Chizoba” //This can't be null name = null var pictureUrl: String? = “some url” //You can keep a null here pictureUrl = null var age = 100 //The compiler assumes non-null age = null fun returnLength(notNull: String): Int { return notNull.length } returnLength(name) returnLength(pictureUrl)
18. var name: String = “Chizoba” //This can't be null name = null var pictureUrl: String? = “some url” //You can keep a null here pictureUrl = null var age = 100 //The compiler assumes non-null age = null fun returnLength(notNull: String): Int { return notNull.length } returnLength(name) returnLength(pictureUrl)
19. var name: String = “Chizoba” //This can't be null name = null var pictureUrl: String? = “some url” //You can keep a null here pictureUrl = null var age = 100 //The compiler assumes non-null age = null fun returnLength(notNull: String): Int { return notNull.length } returnLength(name) returnLength(pictureUrl)
20. var name: String = “Chizoba” //This can't be null name = null var pictureUrl: String? = “some url” //You can keep a null here pictureUrl = null var age = 100 //The compiler assumes non-null age = null fun returnLength(notNull: String): Int { return notNull.length } returnLength(name) returnLength(pictureUrl)
21. var name: String = “Chizoba” //This can't be null name = null var pictureUrl: String? = “some url” //You can keep a null here pictureUrl = null var age = 100 //The compiler assumes non-null age = null fun returnLength(notNull: String): Int { return notNull.length } returnLength(name) returnLength(pictureUrl)
22. var name: String = “Chizoba” //This can't be null name = null var pictureUrl: String? = “some url” //You can keep a null here pictureUrl = null var age = 100 //The compiler assumes non-null age = null fun returnLength(notNull: String): Int { return notNull.length } returnLength(name) returnLength(pictureUrl)
23. var name: String = “Chizoba” //This can't be null name = null var pictureUrl: String? = “some url” //You can keep a null here pictureUrl = null var age = 100 //The compiler assumes non-null age = null fun returnLength(notNull: String): Int { return notNull.length } returnLength(name) returnLength(pictureUrl)
24. var name: String = “Chizoba” //This can't be null name = null var pictureUrl: String? = “some url” //You can keep a null here pictureUrl = null var age = 100 //The compiler assumes non-null age = null fun returnLength(notNull: String): Int { return notNull.length } returnLength(name) returnLength(pictureUrl) Null safety
25. val date: ChronoLocalDate? = LocalDate.now() if (date != null) { println(date.isLeapYear) } if (date != null && date.isLeapYear) { println("It's a leap year!") } if (date is LocalDate) { val month = date.monthValue println(month) }
26. val date: ChronoLocalDate? = LocalDate.now() if (date != null) { println(date.isLeapYear) } if (date != null && date.isLeapYear) { println("It's a leap year!") } if (date is LocalDate) { val month = date.monthValue println(month) }
27. val date: ChronoLocalDate? = LocalDate.now() if (date != null) { println(date.isLeapYear) } if (date != null && date.isLeapYear) { println("It's a leap year!") } if (date is LocalDate) { val month = date.monthValue println(month) }
28. val date: ChronoLocalDate? = LocalDate.now() if (date != null) { println(date.isLeapYear) } if (date != null && date.isLeapYear) { println("It's a leap year!") } if (date is LocalDate) { val month = date.monthValue println(month) } Smart Casts
29. Functions
30. Function definition fun [functionName]:[ReturnType] { }
31. fun multiply(a: Int, b: Int) { return a * b } : Int
32. fun multiply(a: Int, b: Int) { return a * b }
33. fun multiply(a: Int, b: Int) = return a * b
34. fun printName(prefix: String = “Mr”, name: String) { println(“$prefix name”) } Default Arguments
35. “Default Arguments are useful in method overloading”
36. fun printNameWithTitle(prefix: String = “Mr”, name: String) { println(“$prefix name”) } Named Arguments printNameWithTitle(name = “Chizoba”)
37. Scope Functions
38. let val isUserAnEngineer = user?.let { it.occupation.contains(“engineer”, ignoreCase = true) }
39. let val isUserAnEngineer = user.let { checkIfUserisAnEngineer(it) }
40. run user.run { this.name = “techietoby” this.occupation = “twitter addict” }
41. run user.run { name = “techietoby” occupation = “twitter addict” }
42. with instead of: println(“${user.name} is ${user.age}” years old) with(user) { println(“$name is $age years old") }
43. apply user.apply { this.name = “Chizoba” this.occupation = “Software Engineer” }
44. apply user.apply { name = “Chizoba” occupation = “Software Engineer” }
45. apply val currentUser = user.apply { name = “Chizoba” occupation = “Software Engineer” }
46. also val currentUser = User(“Chizoba”, “Software Engineer”) .also { Log.i(TAG, “$it.name logged in”) }
47. Classes
48. Class definition class[className]([Constructor]) { }
49. class User(val id: Int, var name: String) class Company
50. class User(val id: Int, var name: String) class Company
51. fun main() { val company = Company() val user = User(1, “chizoba@gmail.com") user.email = "toby@gmail.com" } class User(val id: Int, var name: String) class Company
52. Special classes
53. Data classes data Class User(val id: Int, val name: String)
54. Data classes val newUser = user.copy(); val newUser = user.copy(10); val newUser = user.copy(name = “techietoby”);
55. Data classes val newUser = user.copy(); val newUser = user.copy(10); val newUser = user.copy(name = “techietoby”);
56. Data classes val newUser = user.copy(); val newUser = user.copy(10); val newUser = user.copy(name = “techietoby”);
57. Data classes val newUser = user.copy(); val newUser = user.copy(10); val newUser = user.copy(name = “techietoby”);
58. Sealed classes sealed class NetworkResponse data class Success(val result: String): NetworkResponse() data class Failure(val error: Error): NetworkResponse()
59. Sealed classes sealed class NetworkResponse data class Success(val result: String): NetworkResponse() data class Failure(val error: Error): NetworkResponse()
60. Sealed classes sealed class NetworkResponse data class Success(val result: String): NetworkResponse() data class Failure(val error: Error): NetworkResponse()
61. Sealed classes sealed class NetworkResponse data class Success(val result: String): NetworkResponse() data class Failure(val error: Error): NetworkResponse()
62. Sealed classes viewModel.data.observe(this, Observer<NetworkResponse> { data -> data ?: return@Observer // skip nulls when(data) { is Success -> showResult(data.result) // smart cast to Success is Failure -> showError(data.error) // smart cast to Failure } })
63. Object keyword
64. object as a declaration object User { fun delete() { … } } fun main() { User.delete() }
65. object as an expression view.setOnClickListener(object: View.OnClickListener { // override methods })
66. Companion object class ProfileActivity : AppCompatActivity() { companion object { fun start(activity: Activity) { startActivity(Intent(activity, ProfileActivity::class.java)) } } } Class HomeActivity: AppCompatActivity() { … ProfileActivity.start(this) }
67. - https://kotlinlang.org/docs/reference/ - https://play.kotlinlang.org Resources
68. Thank you!