Hey Kotlin, How it works?

package com.cwdoh.devfest2017

class Gugu { fun print() { for (i in 1..9) { for (j in 1..9) { print("$i * $j = ${i * j}") } } } }

🤩😲😘😍

package com.cwdoh.devfest2017

class Session { val speaker = "cwdoh" val title: String = "Kotlin: How it works" var room: Int? = null

fun description() = "$speaker's talk: '$title' at room $room" }

package com.cwdoh.devfest2017

class Session { val speaker = "cwdoh" val title: String = "Kotlin: How it works" var room: Int? = null

fun description() = "$speaker's talk: '$title' at room $room" }

class Session { var name = "cwdoh" }

public final class Session { @NotNull private String name = "cwdoh";

@NotNull public final String getName() { return this.name; }

public final void setName(@NotNull String var1) { Intrinsics.checkParameterIsNotNull(var1, "<set-?>"); this.name = var1; } }

class Session { val name = "cwdoh" }

public final class Session { @NotNull private final String name = "cwdoh";

@NotNull public final String getName() { return this.name; } }

class Session { val speaker = "cwdoh"

fun description() { val talks = "$speaker's talks" println(talks) } }

public final class Session { @NotNull private final String speaker = "cwdoh";

@NotNull public final String getSpeaker() { return this.speaker; }

public final void description() { String talks = "" + this.speaker + "'s talks"; System.out.println(talks); } }

package com.cwdoh.devfest2017

class Session { val speaker = "cwdoh" val title: String = "Kotlin: How it works" var room: Int? = null

fun description() = "$speaker's talk: '$title' at room $room" }

class Session { var name: String = "cwdoh" }

public final class Session { @NotNull private String name = "cwdoh";

@NotNull public final String getName() { return this.name; }

public final void setName(@NotNull String var1) { Intrinsics.checkParameterIsNotNull(var1, "<set-?>"); this.name = var1; } }

public static void checkParameterIsNotNull(Object value, String paramName) { if (value == null) { throwParameterIsNullException(paramName); } }

class Session { fun hello(name: String) = "hello, " + name }

public final class Session { @NotNull public final String hello(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); return "hello, " + name; } }

public static void checkParameterIsNotNull(Object value, String paramName) { if (value == null) { throwParameterIsNullException(paramName); } }

class Session { fun hello(name: String) = "hello, " + name fun print() { val name: String = "cwdoh" print(hello(name)) } }

public final class Session { @NotNull public final String hello(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); return "hello, " + name; }

public final void print() { String name = "cwdoh"; String var2 = this.hello(name); System.out.print(var2); } }

class Session { fun hello(name: String) = "hello, " + name

fun print() { val name: String? = null print(hello(name!!)) } }

public final class Session { @NotNull public final String hello(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); return "hello, " + name; }

public final void print() { String name = (String)null; Intrinsics.throwNpe(); String var2 = this.hello(name); System.out.print(var2); } }

NullPointerException? 😎

package com.cwdoh.devfest2017

class Session { val speaker = "cwdoh" val title: String = "Kotlin: How it works" var room: Int? = null

fun description() = "$speaker's talk: '$title' at room $room" }

class Session { val speaker = "cwdoh" val title: String = "Kotlin: How it works" var room: Int? = null

fun description() = "$speaker's talk: '$title' at room $room" }

public final class Session { @NotNull private final String speaker = "cwdoh"; @NotNull private final String title = "Kotlin: How it works"; @Nullable private Integer room;

…

@NotNull public final String description() { return "" + this.speaker + "'s talk: ‘" + this.title + "' at room " + this.room; } }

// access flags 0x11 public final description()Ljava/lang/String; @Lorg/jetbrains/annotations/NotNull;() // invisible L0 LINENUMBER 8 L0 NEW java/lang/StringBuilder DUP INVOKESPECIAL java/lang/StringBuilder.<init> ()V LDC "" INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; ALOAD 0 GETFIELD com/cwdoh/devfest2017/Session.speaker : Ljava/lang/String; INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; LDC "'s talk: '" INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; ALOAD 0 GETFIELD com/cwdoh/devfest2017/Session.title : Ljava/lang/String; INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; LDC "' at room " INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder; ALOAD 0 GETFIELD com/cwdoh/devfest2017/Session.room : Ljava/lang/Integer; INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/Object;)Ljava/lang/StringBuilder; INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String; ARETURN

class NotOpenedClass open class OpenedClass

public final class NotOpenedClass { }

public class OpenedClass { }

interface Interface open class OpenClass class ChildClass: OpenClass(), Interface

fun test() { val child = ChildClass() }

public final class ChildClass extends OpenClass implements Interface {}

public interface Interface {}

public class OpenClass {}

public final class SimpleClassKt { public static final void test() { new ChildClass(); } }

class Person1 constructor(name: String) class Person2(name: String)

public final class Person1 { public Person1(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); super(); } }

public final class Person2 { public Person2(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); super(); } }

class Person constructor(val name: String)

public final class Person { @NotNull private final String name;

@NotNull public final String getName() { return this.name; }

public Person(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); super(); this.name = name; } }

class Person constructor(val name: String) { val greetings: String init { greetings = "hello, $name” } }

public final class Person { @NotNull private String greetings; @NotNull private final String name;

@NotNull public final String getGreetings() { return this.greetings; }

@NotNull public final String getName() { return this.name; }

public Person(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); super(); this.name = name; this.greetings = "hello, " + this.name; } }

class Person constructor(val name: String) { val greetings: String var age: Int = null

constructor(name: String, age: Int): this(name) { this.age = age }

init { greetings = "hello, $name” } }

public final class Person { @NotNull private final String greetings; private int age; …

public Person(@NotNull String name) { Intrinsics.checkParameterIsNotNull(name, "name"); super(); this.name = name; this.age = ((Number)null).intValue(); this.greetings = "hello, " + this.name; }

public Person(@NotNull String name, int age) { Intrinsics.checkParameterIsNotNull(name, "name"); this(name); this.age = age; } }

open class Parent { private val a = println("Parent.a")

constructor(arg: Unit=println("Parent primary constructor arg")) { println("Parent primary constructor") }

init { println("Parent.init") }

private val b = println("Parent.b") }

class Child : Parent { val a = println("Child.a")

init { println("Child.init 1") }

constructor(arg: Unit=println("Child primary constructor arg")) : super() { println("Child primary constructor") }

val b = println("Child.b")

constructor(arg: Int, arg2:Unit= println("Child secondary constructor arg")): this() { println("Child secondary constructor") }

init { println("Child.init 2") } }

fun main(args: Array<String>) { Child(1) }

Child secondary constructor arg Child primary constructor arg Parent primary constructor arg Parent.a Parent.init Parent.b Parent primary constructor Child.a Child.init 1 Child.b Child.init 2 Child primary constructor Child secondary constructor

class Props { var size: Int = 0

val isEmpty: Boolean get() = this.size == 0 }

public final class Props { private int size;

public final int getSize() { return this.size; }

public final void setSize(int var1) { this.size = var1; }

public final boolean isEmpty() { return this.size == 0; } }

class Props { var age: Int = 0 set(value: Int) { age = if (value < 0) 0 else value } }

public final class Props { private int age;

public final int getAge() { return this.age; }

public final void setAge(int value) { this.setAge(value < 0? 0:value); } }

class Props { var age: Int = 0 private set }

public final class Props { private int age;

public final int getAge() { return this.age; }

private final void setAge(int var1) { this.age = var1; } }

class MainActivity : AppCompatActivity() { private var mWelcomeTextView: TextView? = null

override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main)

mWelcomeTextView = findViewById(R.id.msgView) as TextView } }

class MainActivity : AppCompatActivity() { private lateinit var mWelcomeTextView: TextView override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main)

mWelcomeTextView = findViewById(R.id.msgView) as TextView } }

class MainActivity : AppCompatActivity() { private val mWelcomeTextView: TextView override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // Where am I????? // mWelcomeTextView = // findViewById(R.id.msgView) as TextView } }

class MainActivity : AppCompatActivity() { private val messageView : TextView by lazy { // following code will be executed at first access findViewById(R.id.message_view) as TextView }

override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) }

fun onSayHello() { messageView.text = "Hello" } }

class Delegate { operator fun getValue( thisRef: Any?, property: KProperty<*> ): String { // do something // return value }

operator fun setValue( thisRef: Any?, property: KProperty<*>, value: String ) { // do something // assign } }

class Demo { val myName : String by lazy { "John" } }

public final class Demo { // $FF: synthetic field static final KProperty[] $$delegatedProperties = new KProperty[]{ … };

@NotNull private final Lazy myName$delegate;

@NotNull public final String getMyName() { Lazy var1 = this.myName$delegate; KProperty var3 = $$delegatedProperties[0]; return (String)var1.getValue(); }

public Demo() { this.myName$delegate = LazyKt.lazy((Function0)null.INSTANCE); } }

class Demo { val myName : String by lazy { getNameFromPreference() }} initializerdelegate

myName

Lazy<T>

getValue()

{ getNameFromPreference() }initializer

class Demo { val myName : String by lazy { getNameFromPreference() }}

myName

Lazy<T>

getValue() UNINITIALIZED_VALUE

{ getNameFromPreference() }initializer

class Demo { val myName : String by lazy { getNameFromPreference() }}

myName

Lazy<T>

getValue() “John”

{ getNameFromPreference() }initializer

class Demo { val myName : String by lazy { getNameFromPreference() }}

myName

Lazy<T>

getValue() “John”

initializer null

class Demo { val myName : String by lazy { getNameFromPreference() }}

class MainActivity : AppCompatActivity() { private val messageView : TextView by lazy { // I’ll be initialized lazily at first access findViewById(R.id.message_view) as TextView }

override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) }

fun onSayHello() { messageView.text = "Hello" } }

val messageView: TextView by lazy { findViewById(R.id.message_view) as TextView }

property delegate

interface Base { fun printX() }

class BaseImpl(val x: Int) : Base { override fun printX() { print(x) } }

interface A { fun hello(): String }

class B : A { override fun hello() = "Hello!!" }

class C : A by B()

public interface A { @NotNull String hello(); }

public final class B implements A { @NotNull public String hello() { return "Hello!!"; } }

public final class C implements A { // $FF: synthetic field private final B $$delegate_0 = new B();

@NotNull public String hello() { return this.$$delegate_0.hello(); } }

fun String.hello() : String { return "Hello, $this" }

fun main(args: Array<String>) { val whom = "cwdoh" println(whom.hello()) }

// Result Hello, cwdoh

open class C class D: C() fun C.foo() = "c" fun D.foo() = "d" fun printFoo(c: C) { println(c.foo()) } class Demo { fun run() { printFoo(D()) } }

public class C {} public final class D extends C {}

public final class SimpleClassKt { @NotNull public static final String foo(@NotNull C $receiver) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); return "c"; }

@NotNull public static final String foo(@NotNull D $receiver) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); return "d"; }

public static final void printFoo(@NotNull C c) { Intrinsics.checkParameterIsNotNull(c, "c"); String var1 = foo(c); System.out.println(var1); } }

public final class Demo { public final void run() { SimpleClassKt.printFoo((C)(new D())); } }

class Person { fun hello() { println("hello!") } }

fun Person.hello() { println(" ?!!") }

fun main(args: Array<String>) { Person().hello() }

// Result hello!

public final class Person { public final void hello() { String var1 = "hello!"; System.out.println(var1); } }

public final class SimpleClassKt { public static final void hello(@NotNull Person $receiver) { Intrinsics.checkParameterIsNotNull( $receiver, "$receiver"); String var1 = " ?!!"; System.out.println(var1); }

public static final void main(@NotNull String[] args) { Intrinsics.checkParameterIsNotNull(args, "args"); (new Person()).hello(); } }

class D { fun bar() { println("D.bar()") } }

class C { fun baz() { println("C.bar()") } fun D.foo() { bar() // calls D.bar baz() // calls C.baz } fun caller(d: D) { d.foo() } }

public final class C { public final void baz() { String var1 = "C.bar()"; System.out.println(var1); }

public final void foo(@NotNull D $receiver) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); $receiver.bar(); this.baz(); }

public final void caller(@NotNull D d) { Intrinsics.checkParameterIsNotNull(d, "d"); this.foo(d); } }

public final class D { public final void bar() { String var1 = "D.bar()"; System.out.println(var1); } }

data class Length(var centimeters: Int = 0)

var Length.meters: Float get() { return centimeters / 100.0f } set(meters: Float) { this.centimeters = (meters * 100.0f).toInt() }

data class Length(var centimeters: Int = 0)

var Length.meters: Float get() { return centimeters / 100.0f }

set(meters: Float) { this.centimeters = (meters * 100.0f).toInt() }

public final class Length { private int centimeters; ...}

public final class ExtensionsKt { public static final float getMeters( @NotNull Length $receiver) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); return (float)$receiver.getCentimeters() / 100.0F; }

public static final void setMeters( @NotNull Length $receiver, float meters) { Intrinsics.checkParameterIsNotNull($receiver, "$receiver"); $receiver.setCentimeters((int)(meters * 100.0F)); }

...}

fun Any?.toString(): String { if (this == null) return “null"

return toString() }

public final class SimpleClassKt { @NotNull public static final String toString(@Nullable Object $receiver) { return $receiver == null? "null":$receiver.toString(); } }

fun Any?.toString(): String { println("Extension is called.") if (this == null) return "null" return toString() }

fun main(args: Array<String>) { val var1 : Any? = null println(var1.toString())

val str1 : String? = null println(str1.toString())

var str2 : String? = "hello" println(str2.toString())

var str3 : String = "world" println(str3.toString()) }

public final class SimpleClassKt { @NotNull public static final String toString(@Nullable Object $receiver) { String var1 = "Extension is called."; System.out.println(var1); return $receiver == null?"null":$receiver.toString(); }

public static final void main(@NotNull String[] args) { Intrinsics.checkParameterIsNotNull(args, “args");

Object var1 = null; String str1 = toString(var1); System.out.println(str1);

str1 = (String)null; String str2 = toString(str1); System.out.println(str2);

str2 = "hello"; String str3 = toString(str2); System.out.println(str3);

str3 = "world"; String var5 = str3.toString(); System.out.println(var5); } }

Extension is called. null Extension is called. null Extension is called. hello world

fun sing() { println("We will we will rock you") println("(Sing it!)") println("We will we will rock you") }

fun beatbox() { println("pv zk bschk pv zk") }

fun ensemble() { sing() beatbox() sing() beatbox() }

public final class SimpleClassKt { public static final void sing() { String var0 = "We will we will rock you"; System.out.println(var0); var0 = "(Sing it!)"; System.out.println(var0); var0 = "We will we will rock you"; System.out.println(var0); }

public static final void beatbox() { String var0 = "pv zk bschk pv zk"; System.out.println(var0); }

public static final void ensemble() { sing(); beatbox(); sing(); beatbox(); } }

fun sing() { println("We will we will rock you") println("(Sing it!)") println("We will we will rock you") }

fun beatbox() { println("pv zk bschk pv zk") }

fun ensemble() { sing() beatbox() sing() beatbox() }

public final class SimpleClassKt { public static final void sing() { String var1 = "We will we will rock you"; … }

public static final void beatbox() { … }

public static final void ensemble() { String var0 = "We will we will rock you"; System.out.println(var0); var0 = "(Sing it!)"; System.out.println(var0); var0 = "We will we will rock you"; System.out.println(var0); beatbox(); var0 = "We will we will rock you"; System.out.println(var0); var0 = "(Sing it!)"; System.out.println(var0); var0 = "We will we will rock you"; System.out.println(var0); beatbox(); } }

fun log(message: () -> String) { println(message()) }

fun test() { log { "Lorem ipsum dolor sit amet, consectetur ..." } }

public final class SimpleClassKt { public static final void log(@NotNull Function0 message) { Intrinsics.checkParameterIsNotNull(message, "message"); Object var1 = message.invoke(); System.out.println(var1); }

public static final void test() { log((Function0)null.INSTANCE); } }

inline fun trace(message: String) {}

fun doSomething() { print("I'm doing something!") trace("doSomething() is doing something!") }

public final class SimpleClassKt { public static final void trace(@NotNull String message) { Intrinsics.checkParameterIsNotNull(message, "message"); }

public static final void doSomething() { String var0 = "I'm doing something!"; System.out.print(var0); var0 = "doSomething() is doing something!"; } }

inline fun log(message: () -> String) { println(message()) }

fun test() { log { "Lorem ipsum dolor sit amet, consectetur ..." } }

public final class SimpleClassKt { public static final void log(@NotNull Function0 message) { Intrinsics.checkParameterIsNotNull(message, "message"); Object var2 = message.invoke(); System.out.println(var2); }

public static final void test() { String var0 = "Lorem ipsum dolor sit amet, consectetur ..."; System.out.println(var0); } }

inline fun trace(message: ()-> String) {}

fun doSomething() { trace { val receiver = "nurimaru" val sender = "cwdoh" "$sender wanna give $receiver big thank you for good tips." } }

public final class SimpleClassKt { public static final boolean isDebug() { return true; }

public static final void trace(@NotNull Function0 message) { Intrinsics.checkParameterIsNotNull(message, "message"); }

public static final void doSomething() { } }

https://goo.gl/2Tyx4B