The Basic Kotlin

THE BASIC KOTLIN GDG DevFest  Incheon 2017 pluulove

GDG DevFest  Incheon 2017 Android Developer GDG Korea Android Organizer
Android / Kotlin @pluulove

GDG DevFest  Incheon 2017 WHAT THE KOTLIN?

GDG DevFest  Incheon 2017 Statically typed programming language for modern
multiplatform applications 100% interoperable with Java™ and Android™

GDG DevFest  Incheon 2017

GDG DevFest  Incheon 2017 OVERVIEW

GDG DevFest  Incheon 2017 Basic fun main(args: Array<String>): Unit {
println("Hello, world!") }

println("Hello, world!") } Function Keyword

println("Hello, world!") } Function Name

println("Hello, world!") } Parameter Name

println("Hello, world!") } Parameter Type

println("Hello, world!") } Return Type

GDG DevFest  Incheon 2017 fun main(args: Array<String>): Unit { println("Hello,
world!") } Basic Return Type Unit return type can be omitted

GDG DevFest  Incheon 2017 Basic fun main(args: Array<String>) { println("Hello,
world!") }

GDG DevFest  Incheon 2017 val text: String = null val
text: String = null // Error, non-null Type Null Safe

GDG DevFest  Incheon 2017 val text: String? = null Null
Safe

Safe Nullable Keyword

Safe

GDG DevFest  Incheon 2017 val text: String? = null text
= 100.toString() Null Safe val text: String? = null text = 100.toString() // Error, Immutable Data

GDG DevFest  Incheon 2017 val text: String? = null text
= 100.toString() Null Safe Immutable

GDG DevFest  Incheon 2017 var text: String? = null text
= 100.toString() Null Safe Mutable

GDG DevFest  Incheon 2017 if (data != null && data.value
!= null) { data.value.toString(); } Null Safe (2)

GDG DevFest  Incheon 2017 data?.value?.toString() Null Safe (2)

GDG DevFest  Incheon 2017 val l: Int = if (b
!= null) b.length else -1 Null Safe (3) ~ Elvis Operator val l = b?.length ?: -1 https://kotlinlang.org/docs/reference/null-safety.html#elvis-operator

GDG DevFest  Incheon 2017 val l: Int = if (b
!= null) b.length else -1 Null Safe (3) ~ Elvis Operator val l = b?.length ?: -1 Elvis Operator https://kotlinlang.org/docs/reference/null-safety.html#elvis-operator

GDG DevFest  Incheon 2017 fun foo(node: Node): String? { val
parent = node.getParent() ?: return null val name = node.getName() ?:   throw IllegalArgumentException("name expected") // ... } Null Safe (3) ~ Elvis Operator https://kotlinlang.org/docs/reference/null-safety.html#elvis-operator

GDG DevFest  Incheon 2017 Type Inference val s: String =
"Value"

GDG DevFest  Incheon 2017 Type Inference val s = "Value"
// String val c = 'V' // Char val i = 10 // Int val l = 10L // Long val f = 10F // Float val d = 10.0 // Double val b = true // Boolean val sb = StringBuilder() // StringBuilder

GDG DevFest  Incheon 2017 Control Flow if / when /
try

GDG DevFest  Incheon 2017 Control Flow Statement No Return Value
Return Value Expression

GDG DevFest  Incheon 2017 Control Flow (if / when /
try) int a = 10; String value; if (a > 10) { value = "Over 10"; } else { value = "Under 10"; } val a = 10 val value: String if (a > 10) { value = "Over 10" } else { value = "Under 10" } Java Kotlin

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

GDG DevFest  Incheon 2017 val a = 10 val value
= if (a > 10) "Over 10" else "Under 10" Control Flow (if / when / try) Kotlin

try) String value; switch (a) { case 1: value = "one"; break; case 2: value = "two"; break; case 3: value = "three"; break; default: value = "another"; break; } val value: String when { a === 1 -> value = "one" a === 2 -> value = "two" a === 3 -> value = "three" else -> value = "another" } Java Kotlin

try) String value; switch (a) { case 1: value = "one"; break; case 2: value = "two"; break; case 3: value = "three"; break; default: value = "another"; break; } val value = when(a) { 1 -> "one" 2 -> "two" 3 -> "three" else -> "another" } Java Kotlin

GDG DevFest  Incheon 2017 when (x) { parseInt(s) -> print("s
encodes x") in 1..10 -> print("x is in the range") in validNumbers -> print("x is valid") !in 10..20 -> print("x is outside the range") else -> print("none of the above") } Control Flow (if / when / try) Kotlin

encodes x") in 1..10 -> print("x is in the range") in validNumbers -> print("x is valid") !in 10..20 -> print("x is outside the range") else -> print("none of the above") } Control Flow (if / when / try) Kotlin Expression

encodes x") in 1..10 -> print("x is in the range") in validNumbers -> print("x is valid") !in 10..20 -> print("x is outside the range") else -> print("none of the above") } Control Flow (if / when / try) Kotlin Range

encodes x") in 1..10 -> print("x is in the range") in validNumbers -> print("x is valid") !in 10..20 -> print("x is outside the range") else -> print("none of the above") } Control Flow (if / when / try) Kotlin Not in Range

encodes x") in 1..10 -> print("x is in the range") in validNumbers -> print("x is valid") !in 10..20 -> print("x is outside the range") else -> print("none of the above") } Control Flow (if / when / try) Kotlin Optional, statement / expression

GDG DevFest  Incheon 2017 Default Parameter 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); } Java

GDG DevFest  Incheon 2017 Default Parameter 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); } Java Default Default

GDG DevFest  Incheon 2017 Default Parameter fun foo(name: String, number:
Int = 42, toUpperCase: Boolean = false) = (if (toUpperCase) name.toUpperCase() else name) + number Kotlin

GDG DevFest  Incheon 2017 Example class Item { private String
type1; private int type2; private float type3; private float type4; } ▸ setter / getter ▸ hashCode ▸ equals ▸ toString

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; } GDG DevFest  Incheon 2017 Example

GDG DevFest  Incheon 2017 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 = type4; } @Override 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 == null; } @Override 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 result; } @Override public String toString() { return "Item{" + "type1='" + type1 + '\'' + ", type2=" + type2 + ", type3=" + type3 + ", type4=" + type4 + '}'; } } ӡ~~~~~~~~~~׮ ߸ࣻ ୶о/࢏ઁद ߸҃ ੘স਷   ݅݅ೞ૑ ঋ׮ Example

GDG DevFest  Incheon 2017 Data Class data class Item( var
type1: String?, var type2: Int, var type3: Float, var type4: Float)

GDG DevFest  Incheon 2017 Data Class data class Item( var
type1: String?, var type2: Int, var type3: Float, var type4: Float) Data Class Keyword

GDG DevFest  Incheon 2017 Data Class data class Item(var type1:
String?, var type2: Int, var type3: Float, var type4: Float) // Create Single variable val item = Item(1.toString(), 2, 3.toFloat(), 4.toFloat()) // Create Destructuring Declarations val (type1, type2, type3, type4) =   Item(1.toString(), 2, 3.toFloat(), 4.toFloat())

GDG DevFest  Incheon 2017 Singleton 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"); } } Java // Use A.getInstance().b()

GDG DevFest  Incheon 2017 Singleton object A { fun b()
{ println("Singleton") } } Kotlin // Use A.b()

GDG DevFest  Incheon 2017 Smart Casts if (obj is String)
{ print(obj.length) } https://kotlinlang.org/docs/reference/typecasts.html#smart-casts

{ print(obj.length) } Type Check https://kotlinlang.org/docs/reference/typecasts.html#smart-casts

{ print(obj.length) } Smart Casts https://kotlinlang.org/docs/reference/typecasts.html#smart-casts

GDG DevFest  Incheon 2017 Smart Casts when (x) { is
Int -> print(x + 1) is String -> print(x.length + 1) is IntArray -> print(x.sum()) }

Int -> print(x + 1) is String -> print(x.length + 1) is IntArray -> print(x.sum()) } Type Check

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

GDG DevFest  Incheon 2017 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() https://github.com/Kotlin/anko/blob/d5a526512b48c5cd2e3b8f6ff14b153c2337aa22/anko/library/ static/commons/src/dialogs/Toasts.kt // Use in Activity/Fragment toast("Hello World")

GDG DevFest  Incheon 2017 fun Context.toast(message: CharSequence) =   Toast.makeText(this,
message, Toast.LENGTH_SHORT).show() Extension Function

message, Toast.LENGTH_SHORT).show() Extension Function Receiver Type

message, Toast.LENGTH_SHORT).show() Extension Function Function Definition

GDG DevFest  Incheon 2017 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 }

GDG DevFest  Incheon 2017 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

GDG DevFest  Incheon 2017 Higher-Order Functions and Lambdas val list
= listOf(1, 2, 3) list.map({ x: Int -> x * 2 })

= listOf(1, 2, 3) list.map({ x: Int -> x * 2 }) list.map({ x -> x * 2 })

= listOf(1, 2, 3) list.map({ x: Int -> x * 2 }) list.map({ x -> x * 2 }) list.map() { x -> x * 2 }

= 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 }

= 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 }

GDG DevFest  Incheon 2017 Scope apply also run/with let

GDG DevFest  Incheon 2017 Scope (apply, also, run, let) Aࠗఠ
Zө૑ ޙ੗ৌਸ ٜ݅যࠇद׮

GDG DevFest  Incheon 2017 Scope (apply, also, run, let) val
result = StringBuilder().apply { for (letter in 'A'..'Z') { append(letter) } } apply ‣ this : StringBuilder() ‣ return : ഐ୹ೠ Receiver

GDG DevFest  Incheon 2017 val result = StringBuilder().also { for
(letter in 'A'..'Z') { it.append(letter) } } Scope (apply, also, run, let) also ‣ it : StringBuilder() ‣ return : ഐ୹ೠ Receiver

GDG DevFest  Incheon 2017 Scope (apply, also, run, let) val
result = StringBuilder().run { for (letter in 'A'..'Z') { append(letter) } this } run ‣ this : StringBuilder() ‣ return : Block ݃૑݄ ઴

GDG DevFest  Incheon 2017 val result = StringBuilder().let { for
(letter in 'A'..'Z') { it.append(letter) } it } Scope (apply, also, run, let) let ‣ it : StringBuilder() ‣ return : Block ݃૑݄ ઴

GDG DevFest  Incheon 2017 Scope this it self apply also
result run/with let

GDG DevFest  Incheon 2017 Collections Immutable Mutable listOf mutableListOf mapOf
hashMapOf setOf hashSetOf

GDG DevFest  Incheon 2017 Collections val numbers: MutableList<Int> = mutableListOf(1,
2, 3) val readOnlyView: List<Int> = numbers println(numbers) // prints "[1, 2, 3]" numbers.add(4) println(readOnlyView) // prints "[1, 2, 3, 4]" readOnlyView.clear() // -> does not compile https://kotlinlang.org/docs/reference/collections.html

GDG DevFest  Incheon 2017 Collections val _items = mutableListOf<String>() val
items: List<String> = _items.toList() // Convert Immutable val mutableItems = items.toMutableList() // Convert Mutable

GDG DevFest  Incheon 2017 Collections val items = listOf(1, 2,
3, 4) items.first() == 1 items.last() == 4 items.filter { it % 2 == 0 } // returns [2, 4] val rwList = mutableListOf(1, 2, 3) rwList.requireNoNulls() // returns [1, 2, 3] if (rwList.none { it > 6 }) println("No items above 6”) // prints "No items above 6" val item = rwList.firstOrNull() https://kotlinlang.org/docs/reference/collections.html

GDG DevFest  Incheon 2017 Collections Iterable MutableIterable MutableCollection MutableList MutableSet
Collection List Set ArrayList ArrayList Read-only interface Mutable interface Java classes

GDG DevFest  Incheon 2017 Type aliases data class User(val name:
String, val job: String) typealias Pluu = User println(User("Pluu", "Developer")) // User(name=Pluu, job=Developer) println(Pluu("Pluu", "Developer")) // User(name=Pluu, job=Developer)

GDG DevFest  Incheon 2017 Type aliases typealias PluuList = List<Pluu>
val list : PluuList = listOf( User("User Name", "Test1"), Pluu("Pluu Name", "Test2") ) println(list) // [User(name=User Name, job=Test1), User(name=Pluu Name, job=Test2)]

GDG DevFest  Incheon 2017 Type aliases typealias Predicate<T> = (T)
-> Boolean fun foo(p: Predicate<Int>) = p(42) fun main(args: Array<String>) { val f: (Int) -> Boolean = { it > 0 } println(foo(f)) // prints "true" val p: Predicate<Int> = { it > 0 } println(listOf(1, -2).filter(p)) // prints "[1]" }

GDG DevFest  Incheon 2017 KOTLIN FOR ANDROID

GDG DevFest  Incheon 2017 Android Studio 3.0 https://developer.android.com/kotlin/get-started.html

GDG DevFest  Incheon 2017 Android Studio 3.0 ▸ Tools >
Kotlin > Conﬁgure Kotlin in Project

GDG DevFest  Incheon 2017 Project Configuration buildscript { ext.kotlin_version =
'1.1.51' repositories { …… } dependencies { classpath ‘com.android.tools.build:gradle: 3.0.0-rc2' classpath "org.jetbrains.kotlin:kotlin- gradle-plugin:$kotlin_version" } } apply plugin: ‘kotlin-android' dependencies { compile "org.jetbrains.kotlin:kotlin- stdlib-jre7:$kotlin_version" } project build.gradle app build.gradle

GDG DevFest  Incheon 2017 Kotlin Android Extensions app build.gradle apply
plugin: 'kotlin-android-extensions' import kotlinx.android.synthetic.main.<layout>.* // kotlinx.android.synthetic.main.activity_main.*

GDG DevFest  Incheon 2017 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!") } } <TextView android:id="@+id/textView" ... /> Kotlin Android Extensions

GDG DevFest  Incheon 2017 Kotlin Android Extensions ~ Parcelable Support
public class MyParcelable implements Parcelable { private int mData; public int describeContents() { return 0; } public void writeToParcel(Parcel out, int flags) { out.writeInt(mData); } public static final Parcelable.Creator<MyParcelable> CREATOR = new Parcelable.Creator<MyParcelable>() { public MyParcelable createFromParcel(Parcel in) { return new MyParcelable(in); } public MyParcelable[] newArray(int size) { return new MyParcelable[size]; } }; private MyParcelable(Parcel in) { mData = in.readInt(); } } https://github.com/Kotlin/KEEP/blob/master/proposals/extensions/android-parcelable.md

build.gradle apply plugin: 'kotlin-android-extensions' androidExtensions { experimental = true }

@Parcelize class MyParcelable(val data: Int): Parcelable https://github.com/Kotlin/KEEP/blob/master/proposals/extensions/android-parcelable.md

GDG DevFest  Incheon 2017 CHOICE

GDG DevFest  Incheon 2017 ੺ݎಞ ‣ ۞׬ழ࠳ ‣ Functional Programming
‣ Hybrid Language о о૑ח ޙઁٜ ‣ ೠӖ ೠӖ ೠӖ

GDG DevFest  Incheon 2017 ੺ݎಞ ~ Overhead ▸ Kotlin Compiler
ী ੄೧ ࢤࢿغח ௏٘ ▸ ࢤпೞח Ѫࠁ׮ ؊ ݆਷ ௏٘о ࢤࢿ ▸ ೞ૑݅, ೙ਃदী ٜ݅যঠೞח ௏٘ ▸ ms ױਤ ର੉ ▸ Javaࠁ׮ וܽѪ਷ ಂ౟

GDG DevFest  Incheon 2017 ੺ݎಞ ~ Overhead fun test(x: Any)
{ if (x is String) { println(x.length) println(x.length) println(x.length) println(x.length) } } 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); } } Kotlin Decompile

GDG DevFest  Incheon 2017 ੺ݎಞ ~ kapt ▸ Kotlin plugin
supports annotation processors like Dagger or DBFlow. ▸ kotlinc ▶︎ Kotlin Stubs ▶︎ javac ▶︎ Final Code ▸ Clean Build ೧ঠ૑ ઁ؀۽ ز੘ೞӝب ೣ ▸ ঌ ࣻ হח ী۞

GDG DevFest  Incheon 2017 ੺ݎಞ ~ ੗߄৬੄ ੉߹਷ ࠛоמ ▸
Framework Ú Java ▸ Library Ú Java / Kotlin ▸ Your Code Ú Java / Kotlin ▸ Kotlin Compilerо Java Class Codeܳ ݅ٞ ▸ Java to Kotlin, non-null ё୓ী null ਸ ࠁյ ҃਋ …. ী۞ ߊࢤ

GDG DevFest  Incheon 2017 ൞ݎಞ ‣ Java ޙઁ ೧Ѿ ‣
Kotlin Android Extensions ‣ טযաח Kotlin ‣ Simple is Best ‣ Support Jetbrains

GDG DevFest  Incheon 2017 ൞ݎಞ ~ Java ޙઁ ೧Ѿ Java
6 2006 Java 7 2011 Java 8 2014 Android 1.0 2008 Java 7 Support 2013 Java 8 Support Jack / desugar Different for every version Java 9 ????

GDG DevFest  Incheon 2017 ൞ݎಞ ~ Java ޙઁ ೧Ѿ

GDG DevFest  Incheon 2017 https://developer.android.com/about/dashboards/index.html

GDG DevFest  Incheon 2017 ൞ݎಞ ~ טযաח Kotlin ▸ ࠶۽Ӓ
/ ߊ಴ / ҳӖ ࢠ೒ী Kotlin ࢎਊ੉ ૐо ▸ ӝઓ Java 100% ▶︎ Java (N %) + Kotlin (M %) ▸ ׮೯൤, ೠӖ۽ ੘ࢿغח Ӗٜ੉ ࢤӝҊ ੓਺ ▸ ٘٣য, ೠӖ۽ ػ ଼ 1ӂ੉ ୹द ▸ ழפ੄ ௏ౣܽ (୹द ৘੿)

GDG DevFest  Incheon 2017 Simple is Beset ▸ Delegation ▸
Data Class ▸ Singleton ▸ Null Safety ▸ Expression ▸ Destructuring Declarations ▸ Type Checks and Casts

GDG DevFest  Incheon 2017 ൞ݎಞ ~ Support Jetbrains ▸ Show
Kotlin Bytecode ▶︎ Decompile ▸ Decompile ػ Java ௏٘۽ ୓௼ оמ

GDG DevFest  Incheon 2017 Realm Report Q4 2017 Java 85.3%
Kotlin 14.7% 2017/09/25 Java 49.3% Kotlin 50.7% 2018/12/10

GDG DevFest  Incheon 2017 http://tech.lezhin.com/2017/08/03/the-case-against-kotlin

GDG DevFest  Incheon 2017 ֢য়য়য়য়য়য়۱ ೧ঠೠ׮

GDG DevFest  Incheon 2017

GDG DevFest  Incheon 2017 ଵҊ ▸ Kotlin Reference (https://kotlinlang.org/docs/reference/) ▸
Get Started with Kotlin — It is here to stay (https://medium.com/peachstudio/get-started- with-kotlin-it-is-here-to-stay-1eaac85ae6a0) ▸ Kotlin: A New Hope in a Java 6 Wasteland (https://academy.realm.io/posts/droidcon- michael-pardo-kotlin/) ▸ Kotlin੄ ࡄҗ Ӓܿ੗ (http://tech.lezhin.com/2017/08/03/the-case-against-kotlin) ▸ Beyond Kotlin - Advanced features for API Makers (https://speakerdeck.com/agiuliani/ beyond-kotlin-advanced-features-for-api-makers) ▸ Develop your next app with Kotlin - AndroidRennes 2017 (https://speakerdeck.com/agiuliani/ develop-your-next-app-with-kotlin-androidrennes-2017)

GDG DevFest  Incheon 2017 Q&A GDG Slack #android #kotlin (Slack
: http://slack.gdg.kr/)

The Basic Kotlin

The Basic Kotlin

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