Is Kotlin Right For You? - Cream City Code 2018

Sure Java pays the bills for some of us, but there’s no reason why we can’t have fun developing again. Kotlin, developed by JetBrains, has been catching on lately because of its functional nature, null safety, type inference, full interoperability with Java, cross-platform support, and ease of use with Android and Spring. Is this something you and your team should considering spending time to learn?

In this session we will go over what Kotlin is, what problems it solves, and what makes it stand out from other JVM languages. You’ll come away with enough knowledge to decide if this is something you and your team should consider adopting.

Transcript

1. Is Kotlin Right For You? Cream City Code 2018 2018-10-13 Todd Ginsberg @ToddGinsberg Principal Software Developer
3. @ToddGinsberg Who Is This Person? Todd Ginsberg Principal Software Developer @Netspend (a payments company in Austin, TX) Java developer since 1995 Kotlin developer since 2016 Chicago Java User Group Community Director and CFO
4. @ToddGinsberg What’s in a Name? By Editors of Open Street Map - Open Street Map, CC BY-SA Kotlin Island
5. @ToddGinsberg But First… I Java
6. @ToddGinsberg Agenda 1.What is Kotlin? 2.Syntax and Code 3.Community 4.Summary / Wrap-up 5.Q & A
7. @ToddGinsberg What Is Kotlin?
8. @ToddGinsberg What Is Kotlin? Statically typed JVM language, developed by JetBrains Released under Apache 2.0 license JVM 6 or 8 bytecode Also targets ECMAScript 5.1 LLVM compiler can compile to native
9. @ToddGinsberg Major Features 100% interoperable with Java Very easy to learn Fantastic IDE support Large, positive community
10. @ToddGinsberg Major Features Designed to avoid entire classes of defects Null-safe 176,000+ issues on GitHub! 12,171 duplicates on Stack Overflow! Type Inference More than diamond operator or local var (thanks Java 10!)
11. @ToddGinsberg Supported on Android Beep! You can use Kotlin now! - 2017
12. @ToddGinsberg Recommended on Android Beep! Prefer Kotlin over Java! - 2018
13. @ToddGinsberg Spring Framework Support Kotlin is fully supported in Spring Framework 5 Kotlin is an option on start.spring.io Spring @NotNull annotations == Better Kotlin nullability support Comprehensive Kotlin documentation and examples
14. @ToddGinsberg Supported in Gradle
15. @ToddGinsberg Kotlin Adoption MAR 2017 Assess NOV 2017 Trial MAY 2018 Adopt ThoughtWorks Technology Radar
16. @ToddGinsberg Syntax
17. @ToddGinsberg Variables and Values var place: String = "Chicago" place = "Illinois" // OK! val name: String = "Todd" name = "Emma" // Compile Error!
18. @ToddGinsberg Type Inference val d: Int = 2 val description: String = "Todd has $d doughnuts"
19. @ToddGinsberg val d = 2 val description = "Todd has $d doughnuts" Type Inference
20. @ToddGinsberg Equality val name1 = "EXAMPLE" val name2 = "example" // Structural Equality name1 == name2.toUpperCase() // True! // Referential Equality name1 === name2 // False! // Unfortunately… name1 ==== name2 // Compiler Error L
21. @ToddGinsberg Raw Strings val json = "{\n\"name\": \"Todd\"\n}” val json = """ { "name": "Todd" } """
22. @ToddGinsberg Null Safety // Guaranteed to never be null val name: String = "Todd" // May be null val salary: Int? = null
23. @ToddGinsberg var city: String? = "Chicago" // Not allowed, might be null! city.toUpperCase() // Safe traversal city?.toUpperCase() Null-safe Traversal
24. @ToddGinsberg val lowest : Int? = listOf(1, 2, 3).min() val lowest : Int = listOf(1, 2, 3).min() ?: 0 Elvis
25. @ToddGinsberg Combine Safe-Traversal and Elvis println( city?.toUpperCase() ?: ”UNKNOWN” )
26. @ToddGinsberg val lowest: Int? = listOf(1, 2, 3).min() val lowest: Int = listOf(1, 2, 3).min()!! val lowest: Int = emptyList<Int>().min()!! // KotlinNullPointerException! L Manual Override
27. @ToddGinsberg Null Safety Remember the names! ?. == Safe Traversal ?: == Elvis !! == Hold My Beer
28. @ToddGinsberg Expressions – if val status = if (code == 42) { "Success" } else { "Fail" }
29. @ToddGinsberg Expressions – try/catch val number = try { code.toInt() } catch (e: NumberFormatException) { 0 }
30. @ToddGinsberg Expressions – When val result = when(x) { 0 -> "x is 0” in 1..10 -> "x is between 1 and 10” in someSet -> "x is in someSet” parseString(s) -> "the same as parseString” else -> "x doesn't match anything" }
31. @ToddGinsberg when (x) { is Int -> print(x % 2 == 0) is String -> print(x.length + 1) is IntArray -> print(x.sum()) } if(x != null) { println(x.toString()) } Smart Casting
32. @ToddGinsberg Classes class Entity : SomeInterface { // ... }
33. @ToddGinsberg Classes - Inheritance open class Entity : SomeInterface { // ... } class Customer : Entity() { // ... }
34. @ToddGinsberg Properties class Customer(var name: String) { var state: String? = null } val c = Customer("Todd") c.state = "IL" println("${c.name} from ${c.state}") // "Todd from IL"
35. @ToddGinsberg Properties – Set class Customer(var name: String) { var state: String? = null set(value) { field = value?.toUpperCase() } }
36. @ToddGinsberg Properties – Set class Customer(var name: String) { var state: String? = null private set(value) { field = value?.toUpperCase() } }
37. @ToddGinsberg Properties – GET class Customer(var name: String) { var state: String? = null get() { return field?.toUpperCase() } }
38. @ToddGinsberg Property Delegation class Country { val gdp: Int = slowCalculation() } class Country { val gdp: Int by lazy { slowCalculation() } }
39. @ToddGinsberg Class Delegation // Java class MyJavaImpl implements HugeInterface { private final HugeInterface backing; public MyJavaImpl(HugeInterface hi) { backing = hi; } // IMPLEMENT EVERYTHING }
40. @ToddGinsberg Class Delegation // Java class MyJavaImpl extends SomeImplementation { // Implement Some }
41. @ToddGinsberg Class Delegation // Kotlin class MyImpl(h: HugeInterface) : HugeInterface by h { // Implement Some }
42. @ToddGinsberg Let’s Write a POJO! public class Person { public String firstName; public String lastName; }
43. @ToddGinsberg Let’s Write a POJO! public class Person { private String firstName; private String lastName; public String getFirstName() { return firstName; } public void setFirstName(final String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(final String lastName) { this.lastName = lastName; } }
44. @ToddGinsberg Let’s Write a POJO! public class Person { private String firstName; private String lastName; public Person() { } public Person(final String firstName, final String lastName) { this.firstName = firstName; this.lastName = lastName; } public String getFirstName() { return firstName; } public void setFirstName(final String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(final String lastName) { this.lastName = lastName; } }
45. @ToddGinsberg Let’s Write a POJO! import java.util.Objects; public class Person { private String firstName; private String lastName; public Person() { } public Person(final String firstName, final String lastName) { this.firstName = firstName; this.lastName = lastName; } public String getFirstName() { return firstName; } public void setFirstName(final String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(final String lastName) { this.lastName = lastName; } @Override public boolean equals(final Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; final Person person = (Person) o; return Objects.equals(firstName, person.firstName) && Objects.equals(lastName, person.lastName); } @Override public int hashCode() { return Objects.hash(firstName, lastName); } }
46. @ToddGinsberg Let’s Write a POJO! import java.util.Objects; public class Person { private String firstName; private String lastName; public Person() { } public Person(final String firstName, final String lastName) { this.firstName = firstName; this.lastName = lastName; } public String getFirstName() { return firstName; } public void setFirstName(final String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(final String lastName) { this.lastName = lastName; } @Override public boolean equals(final Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; final Person person = (Person) o; return Objects.equals(firstName, person.firstName) && Objects.equals(lastName, person.lastName); } @Override public int hashCode() { return Objects.hash(firstName, lastName); } @Override public String toString() { return "Person{" + "firstName='" + firstName + '\'' + ", lastName='" + lastName + '\'' + '}'; } }
47. @ToddGinsberg Data Classes To The Rescue! data class Person(val firstName: String, val lastName: String) • Getters (and Setters for vars) as Properties • toString() • hashCode() and equals() • And…
48. @ToddGinsberg Copying Data Classes val me = Person("Todd", "Ginsberg") val emma = me.copy(firstName = "Emma") // Person(”Emma", "Ginsberg")
49. @ToddGinsberg Destructuring Data Classes val me = Person("Todd", "Ginsberg") val (first, last) = me // first == “Todd” last == “Ginsberg”
50. @ToddGinsberg FUNctions! fun generateRandomNumber(): Int { return 4 } fun generateRandomNumber(): Int = 4 fun generateRandomNumber() = 4
51. @ToddGinsberg FUNctions – Default Values fun random(offset: Int = 0): Int = offset + 4 random() // 4 random(1) // 5
52. @ToddGinsberg FUNctions – Named Parameters fun combine(first: Int, second: Int): Int = first + second combine(1, 2) // 3 combine(first = 1, second = 2) // 3 combine(second = 2, first = 1) // 3
53. @ToddGinsberg FUNctions – Named & Default fun combine(first: Int, second: Int, third: Int = 0): Int = first + second + third combine(1, 2) // 3 combine(second = 2, first = 1, third = 3) // 6
54. @ToddGinsberg FUNction Names @Test fun `Replicants have a four year lifespan!`() { // ... } @Test fun replicantsHaveAFourYearLifespan() { // ... }
55. @ToddGinsberg fun measureTimeMillis(block: () -> Unit): Long { val start = System.currentTimeMillis() block() return System.currentTimeMillis() - start } val time = measureTimeMillis { someSlowQuery() } High Order FUNctions
56. @ToddGinsberg Extension FUNctions // Java public static boolean isEven(int i) { return i % 2 == 0; } // Kotlin fun Int.isEven(): Boolean = this % 2 == 0 2.isEven() // True!
57. @ToddGinsberg The use Extension // Java try (DatabaseConnection conn = getConnection()) { // ... } // Kotlin getConnection().use { conn -> // ... }
58. @ToddGinsberg The apply Extension // Expression and Statements val p = Person() p.name = "Todd" p.age = 21 // Single Expression val p = Person().apply { name = "Todd" age = 21 }
59. @ToddGinsberg One More Thing On FUNctions… Functions are final by default. Arguments are always final. Functions can be defined in a file, outside of a class. Functions can be defined within another function. Kotlin supports tail recursive functions.
60. @ToddGinsberg What About Checked Exceptions? NO
61. @ToddGinsberg listOf(1, 2, 3, 4) .filter { x -> x % 2 == 0 } .map { y -> y * 2 } // List[4, 8] Lambdas
62. @ToddGinsberg Lambdas listOf(1, 2, 3, 4) .filter { it % 2 == 0 } .map { it * 2 } // List[4, 8]
63. @ToddGinsberg Lambdas Are Closures val ints = listOf(1, 2, 3, 4) var sum = 0 ints.forEach { sum += it } println(sum) // 10
64. @ToddGinsberg Type Aliases fun doSomethingWithMap( ops: Map<SomeType, List<String>> ) { ops.entries // ... }
65. @ToddGinsberg Type Aliases typealias Operations = Map<SomeType, List<String>> fun doSomethingWithMap(ops: Operations) { ops.entries // … }
66. @ToddGinsberg Import Aliases import java.util.Date import java.sql.Date
67. @ToddGinsberg Import Aliases import java.util.Date as UtilDate import java.sql.Date as SqlDate
68. @ToddGinsberg Import Aliases import java.util.Date as SqlDate import java.sql.Date as UtilDate
69. @ToddGinsberg Reified Generics // Ugly val log = Logger.getLogger(Metrics::class.java) // What I want val log = loggerOf<Metrics>()
70. @ToddGinsberg Community
71. @ToddGinsberg Community Resources https://kotlinlang.slack.com • 17,300+ members • Get answers and chat with people who work with the language • Welcoming and helpful • Language authors hang out here Stack Overflow • Actually get meaningful answers • Not uncommon to get many useful answers • Language authors here as well
72. @ToddGinsberg Community KΛTEGORY funKTionale Λrrow
73. @ToddGinsberg Try Kotlin! https://play.kotlinlang.org
74. @ToddGinsberg Learn Kotlin! https://bit.ly/GoogleKotlinClass
75. @ToddGinsberg Learn Kotlin!
76. @ToddGinsberg Fun == Fun Kotlin Thanks, Stack Overflow!
77. @ToddGinsberg Summary
78. @ToddGinsberg Why Kotlin is Right For Me I write far less code. The code I write is more expressive and clear. I avoid whole classes of defects. Allows me to write in a more functional style. Writing Kotlin, for me, is more fun. Plays well with the tools I already use (Spring, IDEA, Gradle)
79. @ToddGinsberg Is Kotlin is Right For You?
80. Than You! @ToddGinsberg https://todd.ginsberg.com todd@ginsberg.com