1. Intro [kotlin-workshop]

Part of https://github.com/jetBrains/kotlin-workshop.

Covers:
- Introduction to Kotlin
- Java to Kotlin converter
- Extension functions

Similar talk might be found here: https://www.youtube.com/watch?v=nrzov-GpWBc.

Transcript

1. Svetlana Isakova Kotlin
2. - modern - pragmatic - Android-friendly Kotlin Programming Language 2017 - official on Android
3. project started Timeline 2010 Feb 2016 Mar 2017 Nov 2017 Kotlin 1.0 Kotlin 1.1 Kotlin 1.2 … …
4. Pragmatic - tooling - Java interop
5. From
6. has good tooling
7. - completion - navigation - refactorings - inspections …
8. can be easily mixed with Java code
9. *.java *.class *.dex compiled to Java bytecode *.kt
10. Kotlin code Java code You can have Java & Kotlin code in one project
11. You can gradually add Kotlin to your existing app
12. Android-friendly
13. Android Studio is based on IntelliJ IDEA
14. just another library for your app rxjava-2.1.2 kotlin-stdlib-1.1.4 6315 10212
15. No Kotlin SDK …just JDK + extensions small runtime jar easy Java interop
16. Gradle & Kotlin Writing Gradle build scripts and plugins in Kotlin
17. try.kotlinlang.org
18. Kotlin Koans
20. J2K converter
21. public class Person {
 private final String name;
 private final int age;
 
 public Person(String name, int age) {
 this.name = name;
 this.age = age;
 }
 
 public String getName() {
 return name;
 }
 
 public int getAge() {
 return age;
 }
 }
22. - equals - hashCode - toString 
 data 
 class Person(val name: String, val age: Int)
23. public class Person {
 private final String name;
 private final int age;
 
 public Person(String name, int age) {
 this.name = name;
 this.age = age;
 }
 
 public String getName() {
 return name;
 }
 
 public int getAge() {
 return age;
 }
 } 
 class Person( val name: String, val age: Int ) person.name person.getName()
24. 
 class Person( val name: String, val age: Int ) person.getName()
25. public class Person {
 private final String name;
 private final int age;
 
 public Person(String name, int age) {
 this.name = name;
 this.age = age;
 }
 
 public String getName() {
 return name;
 }
 
 public int getAge() {
 return age;
 }
 } person.name
26. public void updateWeather(int degrees) {
 String description;
 Colour colour;
 if (degrees < 5) {
 description = "cold";
 colour = BLUE;
 } else if (degrees < 23) {
 description = "mild";
 colour = ORANGE;
 } else {
 description = "hot";
 colour = RED;
 }
 // ...
 } enum Colour { BLUE, ORANGE, RED, /*...*/; }
27. fun updateWeather(degrees: Int) {
 val description: String
 val colour: Colour
 if (degrees < 5) {
 description = "cold"
 colour = BLUE
 } else if (degrees < 23) {
 description = "mild"
 colour = ORANGE
 } else {
 description = "hot"
 colour = RED
 }
 // ...
 }
28. fun updateWeather(degrees: Int) {
 val (description: String, colour: Colour) =
 if (degrees < 5) {
 Pair("cold", BLUE)
 } else if (degrees < 23) {
 Pair("mild", ORANGE)
 } else {
 Pair("hot", RED)
 } // ...
 }
29. fun updateWeather(degrees: Int) {
 val (description, colour) =
 if (degrees < 5) {
 Pair("cold", BLUE)
 } else if (degrees < 23) {
 Pair("mild", ORANGE)
 } else {
 Pair("hot", RED)
 } // ...
 }
30. fun updateWeather(degrees: Int) {
 val (description, colour) = when {
 degrees < 5 -> Pair("cold", BLUE)
 degrees < 23 -> Pair("mild", ORANGE)
 else -> Pair("hot", RED)
 } // ...
 }
31. fun updateWeather(degrees: Int) {
 val (description, colour) = when {
 degrees < 5 -> "cold" to BLUE
 degrees < 23 -> "mild" to ORANGE
 else -> "hot" to RED
 }
 }
32. val (description, colour) = when {
 degrees < 5 -> "cold" to BLUE
 degrees < 23 -> "mild" to ORANGE
 else -> "hot" to RED
 } String description;
 Colour colour; if (degrees < 5) {
 description = "cold";
 colour = BLUE;
 } else if (degrees < 23) {
 description = "mild";
 colour = ORANGE;
 } else {
 description = "hot";
 colour = RED;
 }
33. Extension Functions
34. fun String.lastChar() = get(length - 1) this can be omitted Extension Functions fun String.lastChar() = this.get(this.length - 1)
35. import com.example.util.lastChar import com.example.util.* Extension Functions val c: Char = "abc".lastChar() fun String.lastChar() = get(length - 1)
36. fun String.lastChar() = get(length - 1) Calling Extension Functions from Java code StringExtensions.kt char c = StringExtensionsKt.lastChar("abc"); JavaClass.java import static StringExtensionsKt.lastChar; char c = lastChar("abc");
37. No. Because it’s a regular static method under the hood. fun String.lastChar() = get(length - 1) Extension Functions Is it possible to call a private member of String here?
38. Kotlin library: extensions on collections • filter • map • reduce • count • find • any • flatMap • groupBy • …
39. infix fun <A, B> A.to(that: B) = Pair(this, that) "ANSWER".to(42) "hot" to RED mapOf(0 to "zero", 1 to "one") The to extension function
40. Extensions for Android Toast.makeText(this, "Thank you!”, Toast.LENGTH_SHORT).show() Activity extension function on Activity toast("Thank you!") this.toast("Thank you!")
41. this.startActivity<NewActivity>("ANSWER" to 42) val intent = Intent(this, NewActivity::class.java)
 intent.putExtra("ANSWER", 42)
 startActivity(intent) Extensions for Android
42. Copyright © 2017 https://github.com/JetBrains/kotlin-workshop