Kotlin, Start? Start! (pluu) Android Developer GDG Korea Android Organizer

Transcription

1 Kotlin, Start? Start! (pluu) Android Developer GDG Korea Android Organizer

2 Agenda Kotlin Overview Kotlin??

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10 Basic fun main(args: Array<String>): Unit { println("hello, world!")

11 Basic Function Keyword fun main(args: Array<String>): Unit { println("hello, world!")

12 Basic Function Name fun main(args: Array<String>): Unit { println("hello, world!")

13 Basic Parameter Name fun main(args: Array<String>): Unit { println("hello, world!")

14 Basic Parameter Type fun main(args: Array<String>): Unit { println("hello, world!")

15 Basic Return Type fun main(args: Array<String>): Unit { println("hello, world!")

16 Basic Function Definition fun main(args: Array<String>): Unit { println("hello, world!")

17 Basic Unit return type can be omitted fun main(args: Array<String>): Unit { println("hello, world!")

18 Basic fun main(args: Array<String>) { println("hello, world!")

19 Null Safe val text: String = null // Error, non-null Type

20 Null Safe val text: String? = null

21 Null Safe Nullable Keyword val text: String? = null

22 Null Safe val text: String? = null text = 100.toString() // Error, Immutable Data

23 Null Safe Immutable Keyword val text: String? = null text = 100.toString()

24 Null Safe Mutable Keyword var text: String? = null text = 100.toString()

25 Null Safe if (data!= null && data.value!= null) { data.value.tostring()

26 Null Safe data?.value?.tostring()

27 Control Flow if / when / try

28 Control Flow statement No Return Value expression Return Value

29 Expression ( if / when / try ) Java int val a = 10; String val value: value; String Kotlin if (a > 10) { value = = "Over 10"; else { value = = "Under 10";

30 Expression ( if / when / try ) Java int a = 10; String value; if (a > 10) { value = "Over 10"; else { value = "Under 10"; Kotlin val a = 10 val value: String if (a > 10) { value = "Over 10" else { value = "Under 10"

31 Expression ( if / when / try ) Java int a = 10; String value; if (a > 10) { value = "Over 10"; else { value = "Under 10"; Kotlin val a = 10 val value = if (a > 10) { "Over 10" else { "Under 10"

32 Expression ( if / when / try ) Java int a = 10; String value; if (a > 10) { value = "Over 10"; else { value = "Under 10"; Kotlin val a = 10 val value = if (a > 10) "Over 10" else "Under 10"

33 Expression ( if / when / try ) Kotlin val a = 10 val value = if (a > 10) "Over 10" else "Under 10"

34 Expression ( if / when / try ) Java String value; if (a == 1) { value = "one"; else if (a == 2) { value = "two"; else if (a == 3) { value = "three"; else { value = "another"; Kotlin val value: String if (a === 1) { value = "one" else if (a === 2) { value = "two" else if (a === 3) { value = "three" else { value = "another"

35 Expression ( if / when / try ) Java String value; if (a == 1) { value = "one"; else if (a == 2) { value = "two"; else if (a == 3) { value = "three"; else { value = "another"; Kotlin val value: String when { a === 1 -> value = "one" a === 2 -> value = "two" a === 3 -> value = "three" else -> value = "another"

36 Expression ( if / when / try ) Java String value; if (a == 1) { value = "one"; else if (a == 2) { value = "two"; else if (a == 3) { value = "three"; else { value = "another"; Kotlin val value = when(a) { 1 -> "one" 2 -> "two" 3 -> "three" else -> "another"

37 Expression ( if / when / try ) Kotlin when (x) { parseint(s) -> print("s encodes x") in > print("x is in the range") in validnumbers -> print("x is valid")!in > print("x is outside the range") else -> print("none of the above")

38 Expression ( if / when / try ) Kotlin when (x) { Expression parseint(s) -> print("s encodes x") in > print("x is in the range") in validnumbers -> print("x is valid")!in > print("x is outside the range") else -> print("none of the above")

39 Expression ( if / when / try ) Kotlin when (x) { Range parseint(s) -> print("s encodes x") in > print("x is in the range") in validnumbers -> print("x is valid")!in > print("x is outside the range") else -> print("none of the above")

40 Expression ( if / when / try ) Kotlin when (x) { parseint(s) -> print("s encodes x") in > print("x is in the range") Not In Range in validnumbers -> print("x is valid")!in > print("x is outside the range") else -> print("none of the above")

41 Expression ( if / when / try ) Kotlin when (x) { parseint(s) -> print("s encodes x") in > print("x is in the range") in validnumbers -> print("x is valid") Optional, statement / expression!in > print("x is outside the range") else -> print("none of the above")

42 Default Parameter Java public String foo(string name, int number, boolean touppercase) { return (touppercase? name.touppercase() : name) + number; public String foo(string name, int number) { return foo(name, number, false); public String foo(string name, boolean touppercase) { return foo(name, 42, touppercase); public String foo(string name) { return foo(name, 42);

43 Default Parameter Java public String foo(string name, int number, boolean touppercase) { return (touppercase? name.touppercase() : name) + number; Default : false public String foo(string name, int number) { return foo(name, number, false); public String foo(string name, boolean touppercase) { return foo(name, 42, touppercase); Default : 42 public String foo(string name) { return foo(name, 42);

44 Default Parameter fun foo(name: String, number: Int = 42, touppercase: Boolean = false) = (if (touppercase) name.touppercase() else name) + number

45 Default Parameter fun foo(name: String, number: Int = 42, touppercase: Boolean = false) = (if (touppercase) name.touppercase() else name) + number

46 Example setter / getter hashcode equals tostring class Item { private String type1; private int type2; private float type3; private float type4;

47 public String gettype1() { return type1; Example class Item { private String type1; private int type2; private float type3; private float type4; public Item(String type1, int type2, float type3, float type4) { this.type1 = type1; this.type2 = type2; this.type3 = type3; this.type4 = type4;

48 class Item { private String type1; private int type2; private float type3; private float type4; public Item(String type1, int type2, float type3, float type4) { this.type1 = type1; this.type2 = type2; this.type3 = type3; this.type4 = type4; public String gettype1() { return type1; public void settype1(string type1) { this.type1 = type1; public int gettype2() { return type2; public void settype2(int type2) { this.type2 = type2; public float gettype3() { return type3; public void settype3(float type3) { this.type3 = type3; public float gettype4() { return type4; public void settype4(float type4) { this.type4 = public boolean equals(object o) { if (this == o) return true; if (o == null getclass()!= o.getclass()) return false; Item item = (Item) o; if (type2!= item.type2) return false; if (Float.compare(item.type3, type3)!= 0) return false; if (Float.compare(item.type4, type4)!= 0) return false; return type1!= null? type1.equals(item.type1) : item.type1 == public int hashcode() { int result = type1!= null? type1.hashcode() : 0; result = 31 * result + type2; result = 31 * result + (type3!= +0.0f? Float.floatToIntBits(type3) : 0); result = 31 * result + (type4!= +0.0f? Float.floatToIntBits(type4) : 0); return public String tostring() { return "Item{" + "type1='" + type1 + '\'' + ", type2=" + type2 + ", type3=" + type3 + ", type4=" + type4 + ''; Field? setter / getter hashcode equals tostring

49 Data Class data class Item( var type1: String?, var type2: Int, var type3: Float, var type4: Float)

50 Data Class data Keyword data class Item( var type1: String?, var type2: Int, var type3: Float, var type4: Float)

51 Data Class equals() / hashcode() tostring() componentn() functions copy() // Destructuring Declarations val jane = User("Jane", 35) val (name, age) = jane println("$name, $age years of age") // prints "Jane, 35 years of age"

52 Singleton Class Java public class A { private static final A instance = new A(); private A() { public static A getinstance() { return instance; public void b() { System.out.println("Singleton"); Custom Method

53 Object Class object A { fun b() { println("singleton") // Use A.b()

54 Object Class object A { fun b() { Object declarations println("singleton")

55 Type Inference val s: String = "Value"

56 Type Inference val s = "Value" val c = 'V' val i = 10 val l = 10L val f = 10F val d = 10.0 val b = true val sb = StringBuilder() // String // Char // Int // Long // Float // Double // Boolean // StringBuilder

57 Smart Casts if (obj is String) { print(obj.length)

58 Smart Casts if (obj is String) { print(obj.length) Type Check

59 Smart Casts if (obj is String) { print(obj.length) Smart Casts

60 Smart Casts when (x) { is Int -> print(x + 1) is String -> print(x.length + 1) is IntArray -> print(x.sum())

61 Smart Casts when (x) { is Int -> print(x + 1) is String -> print(x.length + 1) Type Check is IntArray -> print(x.sum())

62 Smart Casts when (x) { is Int -> print(x + 1) is String -> print(x.length + 1) Smart Casts is IntArray -> print(x.sum())

63 Smart Casts when (x) { is Int -> print(x + 1) is String -> print(x.length + 1) is IntArray -> print(x.sum()) Type Check

64 Smart Casts when (x) { is Int -> print(x + 1) is String -> print(x.length + 1) is IntArray -> print(x.sum()) Smart Casts

65 Smart Casts when (x) { is Int -> print(x + 1) is String -> print(x.length + 1) is IntArray -> print(x.sum()) Type Check

66 Smart Casts when (x) { is Int -> print(x + 1) is String -> print(x.length + 1) is IntArray -> print(x.sum()) Smart Casts

67 Extension Function inline fun Fragment.toast(message: CharSequence): Unit = activity.toast(message) fun Context.toast(message: CharSequence) = Toast.makeText(this, message, Toast.LENGTH_SHORT).show() // Use in Activity/Fragment toast("hello World") commons/src/dialogs/toasts.kt

68 Extension Function fun Context.toast(message: CharSequence) = Toast.makeText(this, message, Toast.LENGTH_SHORT).show()

69 Extension Function fun Context.toast(message: CharSequence) = Toast.makeText(this, message, Toast.LENGTH_SHORT).show() Receiver Type

70 Extension Function fun Context.toast(message: CharSequence) = Toast.makeText(this, message, Toast.LENGTH_SHORT).show() Function Definition

71 Extension Function fun Context.toast(message: CharSequence) = Toast.makeText(this, message, Toast.LENGTH_SHORT).show() Function Body

72 Higher-Order Functions and Lambdas fun <T, R> List<T>.map(transform: (T) -> R): List<R> { val result = arraylistof<r>() for (item in this) result.add(transform(item)) return result

73 Higher-Order Functions and Lambdas fun <T, R> List<T>.map(transform: (T) -> R): List<R> { val result = arraylistof<r>() for (item in this) result.add(transform(item)) return result Function Type

74 Higher-Order Functions and Lambdas val list = listof(1, 2, 3) list.map({ x: Int -> x * 2 )

75 Higher-Order Functions and Lambdas val list = listof(1, 2, 3) list.map({ x: Int -> x * 2 ) list.map({ x -> x * 2 )

76 Higher-Order Functions and Lambdas val list = listof(1, 2, 3) list.map({ x: Int -> x * 2 ) list.map({ x -> x * 2 ) list.map() { x -> x * 2

77 Higher-Order Functions and Lambdas val list = listof(1, 2, 3) list.map({ x: Int -> x * 2 ) list.map({ x -> x * 2 ) list.map() { x -> x * 2 list.map { x -> x * 2

78 Higher-Order Functions and Lambdas val list = listof(1, 2, 3) list.map({ x: Int -> x * 2 ) list.map({ x -> x * 2 ) list.map() { x -> x * 2 list.map { x -> x * 2 list.map { it * 2

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80 1. Kotlin? / / / Functional Programming Hybrid Language Best Practices

81 2.

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83 3. Function Programming FP (ex, Predicate, High-Order Function)

84 3. FP.

85 3. FP. Groovy Lazy Lambda Clojure Pure Function Dispatch Reduce High-Order Function Monad Scala Currying

86 4. Overhead Kotlin Compiler ms Java

87 4. Overhead Kotlin fun test(x: Any) { if (x is String) { println(x.length) println(x.length) println(x.length) println(x.length) Decompile public static final void test(@notnull Object x) { Intrinsics.checkParameterIsNotNull(x, "x"); if (x instanceof String) { int var1 = ((String)x).length(); System.out.println(var1); var1 = ((String)x).length(); System.out.println(var1); var1 = ((String)x).length(); System.out.println(var1); var1 = ((String)x).length(); System.out.println(var1);

88 5. kapt Kotlin plugin supports annotation processors like Dagger or DBFlow. apply plugin: 'kotlin-kapt' kotlinc Kotlin Stubs javac Final Code Clean Build

89 6. Framework Library Your Code Java Java / Kotlin Java / Kotlin Kotlin Compiler Java Class Code Java to Kotlin, non-null null.

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91 1. Java Java Java Java Java 9???? Android Java 7 Support 2013 Java 8 Support Jack / desugar Different for every version

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94 2. Kotlin Android Extensions Kotlin Android Extensions View Binding, ViewHolder (1.1.4), Parcelable (1.1.4) Extension Function Lazy Anko

95 2. Kotlin Android Extensions import kotlinx.android.synthetic.main.activity_main.* class MyActivity : Activity() { override fun oncreate(savedinstancestate: Bundle?) { super.oncreate(savedinstancestate) setcontentview(r.layout.activity_main) textview.settext("hello, world!") Kotlin Android Extensions <TextView android:id="@+id/textview"... />

96 2. Kotlin Android Extensions apply plugin: 'kotlin-android-extensions' import kotlinx.android.synthetic.main.<layout>.* // kotlinx.android.synthetic.main.activity_main.*

97 3. Kotlin GitHub (2017/09/20 ) Stars : 5 Language : 30

98 3. Kotlin / / Kotlin Java 100% Java (N %) + Kotlin (M %),, 1 ( )

99 4. Simple is Best Delegation Data Class Singleton Null Safety Expression Destructuring Declarations Type Checks and Casts

100 5. Code Scope val person = Person().apply { name = "Pluu" age = 1 money = 1 phone = " " // More

101 5. Code Scope val person = Person().apply { name = "Pluu" age = 1 money = 1 phone = " " // More apply Calls the specified function [block] with `this` value as its receiver and returns `this` value.

102 5. Code Scope val person = Person().apply {

103 6. IntelliJ Show Kotlin Bytecode Decompile Decompile Java

104 Preferred / Used Kotlin

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107 Any.kt

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111 2017 Kotlin ( 3~4 ) GDG Kotlin Kotlin (Kotlin Reference, Twitter, Medium, Qiita) Kotlin ( )

112 , best practice

113 Action Item! Kotlin X, Kotlin Convert Java File to Kotlin File Show Kotlin Bytecode

114 Kotlin Reference ( Get Started with Kotlin It is here to stay ( Kotlin: A New Hope in a Java 6 Wasteland ( droidcon-michael-pardo-kotlin/) Kotlin (

115 Q&A GDG Slack #android #kotlin (Slack :