Jake Wharton A Builder's Intro to Kotlin
A presentation at Gradle Summit in June 2017 in Palo Alto, CA, USA by Jake Wharton
Jake Wharton A Builder's Intro to Kotlin
Kotlin?
Why Kotlin?
Plugin Author
Plugin Author Buildscript Author
Plugin Author Buildscript Author App Developer
val firstName: String = "Jake" val lastName: String? = null
val firstName: String = "Jake" val lastName: String? = null
val firstName: String = "Jake" val lastName: String? = null
val firstName: String = "Jake" val lastName: String? = null
val firstName: String = "Jake" val lastName: String? = null
val firstName = "Jake" val lastName: String? = null
class User {
public String getName() {
// ...
}
public void setName(String name) {
// ...
} }
// ^^^ Java
class User {
public String getName() {
// ...
} X
public void setName(String name) {
// ...
} Y } Z
// ^^^ Java vvv Kotlin
val user = User() println ( "Name is "
class User {
public String getName() {
// ...
} X
public void setName(String name) {
// ...
} Y } Z
// ^^^ Java vvv Kotlin
val user = User() println ( "Name is "
class User {
public String getName() {
// ...
} X
public void setName(String name) {
// ...
} Y } Z
// ^^^ Java vvv Kotlin
val user = User() println ( "Name is ${ user. name } " ) X
class User {
public String getName() {
// ...
} X
public void setName(String name) {
// ...
} Y } Z
// ^^^ Java vvv Kotlin
val user = User() println ( "Name is $ user " ) X
class User {
public String getName() {
// ...
} X
public void setName(String name) {
// ...
} Y } Z
// ^^^ Java vvv Kotlin
val user = User() println ( "Name is $ user " ) X
class User {
"Jake" }
// ^^^ Kotlin
class User {
"Jake" }
// ^^^ Kotlin vvv Java User user = new User(); System. out .println( "Name is "
class User {
"Jake" }
// ^^^ Kotlin vvv Java User user = new User(); System. out .println( "Name is "
class User {
"Jake" }
// ^^^ Kotlin vvv Java User user = new User(); System. out .println( "Name is "
user.setName( "Jane" );
class User {
"Jake" }
// ^^^ Kotlin vvv Java User user = new User(); System. out .println( "Name is "
user.setName( "Jane" );
val user = User()
val user = User() user = User()
val user = User() user = User()
var currentUser = User() currentUser = User()
fun Date.isTuesday(): Boolean {
2 }
fun Date.isTuesday(): Boolean {
2 }
val epoch = Date( 1970 , 0 , 0 ) if (epoch. isTuesday ()) {
println ( "The epoch was a Tuesday." ) } else {
println ( "The epoch was not a Tuesday." ) }
fun Date.isTuesday(): Boolean {
2 }
val epoch = Date( 1970 , 0 , 0 ) if (epoch. isTuesday ()) {
println ( "The epoch was a Tuesday." ) } else {
println ( "The epoch was not a Tuesday." ) }
fun Date.isTuesday(): Boolean {
2 }
val epoch = Date( 1970 , 0 , 0 ) if (epoch. isTuesday ()) {
println ( "The epoch was a Tuesday." ) } else {
println ( "The epoch was not a Tuesday." ) } // ^^^ Kotlin vvv Java DateKt. isTuesday (date)
val executor = Executors.newSingleThreadExecutor(); executor. execute { B println ( "Background thread!" ) } X
val executor = Executors.newSingleThreadExecutor();
val foo = Foo() executor. execute (foo::printIt)
class Foo {
fun printIt() { B
println(
"Background thread!" ) } X
}
val executor = Executors.newSingleThreadExecutor();
val foo = Foo() executor. execute (foo::printIt)
class Foo {
fun printIt() { B
println(
"Background thread!" ) } X
}
fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
// ... }
fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
// ... }
fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
// ... } A
val items = listOf ( 1 , 2 , 3 ) val odds = items. filter ( { item -> item % 2 != 0 } ) B
fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
// ... } A
val items = listOf ( 1 , 2 , 3 ) val odds = items. filter ( { item -> item % 2 != 0 } ) B
fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
// ... } A
val items = listOf ( 1 , 2 , 3 ) val odds = items. filter ( { it % 2 != 0 } ) B
fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
// ... } A
val items = listOf ( 1 , 2 , 3 ) val odds = items. filter () B { it % 2 != 0 }
fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
// ... } A
val items = listOf ( 1 , 2 , 3 ) val odds = items. filter { it % 2 != 0 }
fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
// ... } A
val items = listOf ( 1 , 2 , 3 ) val oddList = items. filter { it % 2 != 0 }
val oddSet = items. filterTo(mutableListOf()) { it % 2 != 0 }
fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
// ... } A
val items = listOf ( 1 , 2 , 3 ) val odds = items. filter { it % 2 != 0 }
inline fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
// ... } A
val items = listOf ( 1 , 2 , 3 ) val odds = items. filter { it % 2 != 0 }
inline fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
val destination = mutableListOf < T
()
for (item in this ) {
if (predicate(item)) destination.add(item) } B
return destination } A
val items = listOf ( 1 , 2 , 3 ) val odds = items. filter { it % 2 != 0 } val destination = mutableListOf <
() for (item in
) {
if ( item ) destination.add(item) } G
destination
inline fun < T
List< T .filter(predicate: ( T ) -> Boolean): List< T {
val destination = mutableListOf < T
()
for (item in this ) {
if (predicate(item)) destination.add(item) } B
return destination } A
val items = listOf ( 1 , 2 , 3 ) val destination = mutableListOf <Int>() for (item in items ) {
if (item % 2 != 0 ) destination.add(item) } G
val odds = destination
filter
it
fun < T
List< T .filterIsInstance(c: Class< T ): List< T {
val destination = mutableListOf < T
() for (item in this ) {
if (c.isInstance(item)) destination.add(item)
}
return destination } A
fun < T
List< T .filterIsInstance(c: Class< T ): List< T {
val destination = mutableListOf < T
() for (item in this ) {
if (c.isInstance(item)) destination.add(item) } G
return destination } A
fun < T
List< T .filterIsInstance(): List< T {
val destination = mutableListOf < T
() for (item in this ) {
if (item in
T ) destination.add(item) } G
return destination } A
c: Class<T>
c.isInstance(
)
fun < T
List< T .filterIsInstance(): List< T {
val destination = mutableListOf < T
() for (item in this ) {
if (item in
T ) destination.add(item) } G
return destination } A
inline fun < T
List< T .filterIsInstance(): List< T {
val destination = mutableListOf < T
() for (item in this ) {
if (item in
T ) destination.add(item) } G
return destination } A
inline fun < reified T
List< T .filterIsInstance(): List< T {
val destination = mutableListOf < T
() for (item in this ) {
if (item in
T ) destination.add(item) } G
return destination } A
inline fun < reified T
List< T .filterIsInstance(): List< T {
val destination = mutableListOf < T
() for (item in this ) {
if (item in
T ) destination.add(item) } G
return destination } A
inline fun < reified T
List< T .filterIsInstance(): List< T {
val destination = mutableListOf < T
() for (item in this ) {
if (item in
T ) destination.add(item)
}
return destination } A val list = listOf ( 1 , 2f , 3 , 4f ) val ints = list. filterIsInstance <Int>()
inline fun < reified T
List< T .filterIsInstance(): List< T {
val destination = mutableListOf < T
() for (item in this ) {
if (item in
T ) destination.add(item)
}
return destination } A val list = listOf ( 1 , 2f , 3 , 4f ) val ints = list. filterIsInstance <Int>()
ALOAD 7
INSTANCEOF java/lang/Integer IFEQ L8 ALOAD 5
ALOAD 7
INVOKEINTERFACE java/util/Collection.add (Ljava/lang/Object;)Z
class User { D
"Jake" } A
class User(name: String) { D
val name = name } A
"
Jake"
class User( val
name : String) { } A
class User( val
name : String)
class User( val
name : String)
val jake = User( "Jake" ) println ( "Hello, $ jake !" )
class User( val
name : String)
val jake = User( "Jake" ) println ( "Hello, $ jake !" )
Hello, User@3a71f4dd !
data class User( val
name : String)
val jake = User( "Jake" ) println ( "Hello, $ jake !" )
Hello, User@3a71f4dd !
@3a71f4dd data class User( val
name : String)
val jake = User( "Jake" ) println ( "Hello, $ jake !" )
Hello, User(name=Jake) !
data class User( val
name : String)
val jake = User( "Jake" ) println ( "Hello, $ jake !" )
Hello, User(name=Jake) !
class UserPersisence(db: SqlDatabase) {
private val deleteByName
= db.createStatement( "DELETE FROM user WHERE name = ?" )
fun delete(name: String) {
deleteByName .bind( 1 , name)
deleteByName .execute() } }
class UserPersisence(db: SqlDatabase) {
private val deleteByName
= db.createStatement( "DELETE FROM user WHERE name = ?" )
fun delete(name: String) {
deleteByName .bind( 1 , name)
deleteByName .execute() } B
} A
class UserPersisence(db: SqlDatabase) {
private val deleteByName by lazy {
db.createStatement( "DELETE FROM user WHERE name = ?" )
} C
fun delete(name: String) {
deleteByName .bind( 1 , name)
deleteByName .execute() } B
} A
val deleteByName by lazy {
db.createStatement( "DELETE FROM user WHERE name = ?" ) } C
val deleteByName by lazy {
db.createStatement( "DELETE FROM user WHERE name = ?" ) } C var name by Delegates.observable( "Jane" ) { prop, old, new ->
println ( "Name changed from $ old to $ new " ) }
val deleteByName by lazy {
db.createStatement( "DELETE FROM user WHERE name = ?" ) } C var name by Delegates.observable( "Jane" ) { prop, old, new ->
println ( "Name changed from $ old to $ new " ) }
var address by Delegates.notNull<String>()
val deleteByName by lazy {
db.createStatement( "DELETE FROM user WHERE name = ?" ) } C var name by Delegates.observable( "Jane" ) { prop, old, new ->
println ( "Name changed from $ old to $ new " ) }
var address by Delegates.notNull<String>() val nameView by bindView <TextView>(R. id . name )
val deleteByName by lazy {
db.createStatement( "DELETE FROM user WHERE name = ?" ) } C var name by Delegates.observable( "Jane" ) { prop, old, new ->
println ( "Name changed from $ old to $ new " ) }
var address by Delegates.notNull<String>() val nameView by bindView <TextView>(R. id . name )
fun main( vararg args: String) = runBlocking<Unit> {
val jobs = List ( 100_000 ) {
launch(CommonPool) {
delay( 1000L )
print ( "." )
} }
jobs.forEach { it.join() } }
Plugin Author Buildscript Author App Developer
App Developer
Plugin Author
Buildscript Author
apply plugin : 'org.jetbrains.kotlin.jvm'
apply plugin : 'org.jetbrains.kotlin.jvm' src/ main/ java/ Fizz.java Buzz.java
apply plugin : 'org.jetbrains.kotlin.jvm' src/ main/ java/ Fizz.java Buzz.kt
*.java *.kt
*.java *.kt kotlinc
*.java *.kt kotlinc
*.java *.kt kotlinc javac
*.java *.kt kotlinc javac
*.java *.kt kotlinc javac
kotlin-stdlib *.java *.kt kotlinc javac
kotlin-stdlib *.java *.kt kotlinc javac
kotlin-stdlib *.java *.kt kotlinc javac
project(':some-library')
apply plugin : 'org.jetbrains.kotlin.jvm'
apply plugin : 'org.jetbrains.kotlin.jvm'
apply plugin : 'org.jetbrains.kotlin.android '
apply plugin : 'org.jetbrains.kotlin.jvm'
apply plugin : 'org.jetbrains.kotlin.android'
apply plugin : 'kotlin2js '
apply plugin : 'org.jetbrains.kotlin.jvm'
apply plugin : 'org.jetbrains.kotlin.android'
apply plugin : 'kotlin2js'
apply plugin : 'konan'
apply plugin : 'org.jetbrains.kotlin.jvm'
apply plugin : 'org.jetbrains.kotlin.android'
apply plugin : 'kotlin2js'
apply plugin : 'konan'
or apply plugin : 'org.jetbrains.kotlin.platform.common ' apply plugin : 'org.jetbrains.kotlin.platform.jvm ' apply plugin : 'org.jetbrains.kotlin.platform.js ' apply plugin : 'konan'
Plugin Author Buildscript Author App Developer
Buildscript Author
Plugin Author
App Developer
apply plugin : 'org.jetbrains.kotlin.jvm' apply plugin : 'org.jetbrains.kotlin.kapt' sourceCompatibility = JavaVersion. VERSION_1_8 targetCompatibility = JavaVersion. VERSION_1_8 dependencies { compile deps. kotlin .stdLibJre8 compile deps. javaPoet
compile deps. autoCommon
compileOnly deps. autoService
kapt deps. autoService
testCompile deps. junit
testCompile deps. truth
testCompile deps. compileTesting
}
apply plugin : 'org.jetbrains.kotlin.jvm' apply plugin : 'org.jetbrains.kotlin.kapt' sourceCompatibility = JavaVersion. VERSION_1_8 targetCompatibility = JavaVersion. VERSION_1_8 dependencies { compile deps. kotlin .stdLibJre8 compile deps. javaPoet
compile deps. autoCommon
compileOnly deps. autoService
kapt deps. autoService
testCompile deps. junit
testCompile deps. truth
testCompile deps. compileTesting
}
apply( plugin : 'org.jetbrains.kotlin.jvm' ) X
apply plugin : 'org.jetbrains.kotlin.kapt' sourceCompatibility = JavaVersion. VERSION_1_8 targetCompatibility = JavaVersion. VERSION_1_8 dependencies { compile deps. kotlin .stdLibJre8 compile deps. javaPoet
compile deps. autoCommon
compileOnly deps. autoService
kapt deps. autoService
testCompile deps. junit
testCompile deps. truth
testCompile deps. compileTesting
}
apply( singletonMap ( 'plugin' , 'org.jetbrains.kotlin.jvm' )) X
apply plugin : 'org.jetbrains.kotlin.kapt' sourceCompatibility = JavaVersion. VERSION_1_8 targetCompatibility = JavaVersion. VERSION_1_8 dependencies { compile deps. kotlin .stdLibJre8 compile deps. javaPoet
compile deps. autoCommon
compileOnly deps. autoService
kapt deps. autoService
testCompile deps. junit
testCompile deps. truth
testCompile deps. compileTesting
}
apply( singletonMap ( 'plugin' , 'org.jetbrains.kotlin.jvm' )) X
apply plugin : 'org.jetbrains.kotlin.kapt' sourceCompatibility = JavaVersion. VERSION_1_8 targetCompatibility = JavaVersion. VERSION_1_8 dependencies { compile deps. kotlin .stdLibJre8 compile deps. javaPoet
compile deps. autoCommon
compileOnly deps. autoService
kapt deps. autoService
testCompile deps. junit
testCompile deps. truth
testCompile deps. compileTesting
}
apply( singletonMap ( 'plugin' , 'org.jetbrains.kotlin.jvm' )) X
apply plugin : 'org.jetbrains.kotlin.kapt' sourceCompatibility = JavaVersion. VERSION_1_8 targetCompatibility = JavaVersion. VERSION_1_8 dependencies { compile deps. kotlin .stdLibJre8 compile deps. javaPoet
compile deps. autoCommon
compileOnly deps. autoService
kapt deps. autoService
testCompile deps. junit
testCompile deps. truth
testCompile deps. compileTesting
}
apply( singletonMap ( 'plugin' , 'org.jetbrains.kotlin.jvm' )) X
apply plugin : 'org.jetbrains.kotlin.kapt' sourceCompatibility = JavaVersion. VERSION_1_8 targetCompatibility = JavaVersion. VERSION_1_8 dependencies { compile deps. kotlin .stdLibJre8 compile(deps. javaPoet )
compile deps. autoCommon
compileOnly deps. autoService
kapt deps. autoService
testCompile deps. junit
testCompile deps. truth
testCompile deps. compileTesting
}
apply( singletonMap ( 'plugin' , 'org.jetbrains.kotlin.jvm' )) X
apply plugin : 'org.jetbrains.kotlin.kapt' sourceCompatibility = JavaVersion. VERSION_1_8 targetCompatibility = JavaVersion. VERSION_1_8 dependencies { compile deps. kotlin .stdLibJre8 compile(deps. javaPoet )
compile deps. autoCommon
compileOnly deps. autoService
kapt deps. autoService
testCompile deps. junit
testCompile deps. truth
testCompile deps. compileTesting
}
android { // ...
testOptions {
unitTests.all {
systemProperty( 'robolectric.dependency.repo.id' , 'example-nexus' ) systemProperty( 'robolectric.dependency.repo.url' ,
'https://nexus.example.com/content/groups/public' )
} }
}
android { // ...
testOptions {
unitTests.all {
systemProperty( 'robolectric.dependency.repo.id' , 'example-nexus' ) systemProperty( 'robolectric.dependency.repo.url' ,
'https://nexus.example.com/content/groups/public' )
} }
}
android { // ...
testOptions {
unitTests.all {
systemProperty( 'robolectric.dependency.repo.id' , 'example-nexus' ) systemProperty( 'robolectric.dependency.repo.url' ,
'https://nexus.example.com/content/groups/public' ) } }
apply plugin : 'org.jetbrains.kotlin.jvm' apply plugin : 'org.jetbrains.kotlin.kapt' sourceCompatibility = JavaVersion. VERSION_1_8 targetCompatibility = JavaVersion. VERSION_1_8 dependencies { compile deps. kotlin .stdLibJre8 compile deps. javaPoet
compile deps. autoCommon
compileOnly deps. autoService
kapt deps. autoService
testCompile deps. junit
testCompile deps. truth
testCompile deps. compileTesting
} A java build.gradle
apply {
plugin( 'org.jetbrains.kotlin.jvm' )
plugin( 'org.jetbrains.kotlin.kapt' )
} java {
sourceCompatibility = JavaVersion. VERSION_1_8
targetCompatibility = JavaVersion. VERSION_1_8
}
dependencies { compile(deps. kotlin .stdLibJre8)
compile(deps. javaPoet )
compile(deps. autoCommon )
compileOnly(deps. autoService )
kapt(deps. autoService )
testCompile(deps. junit )
testCompile(deps. truth )
testCompile(deps. compileTesting )
} A build.gradle.kts
apply {
plugin( 'org.jetbrains.kotlin.jvm' )
plugin( 'org.jetbrains.kotlin.kapt' )
} java {
sourceCompatibility = JavaVersion. VERSION_1_8
targetCompatibility = JavaVersion. VERSION_1_8
}
dependencies { compile(deps. kotlin .stdLibJre8)
compile(deps. javaPoet )
compile(deps. autoCommon )
compileOnly(deps. autoService )
kapt(deps. autoService )
testCompile(deps. junit )
testCompile(deps. truth )
testCompile(deps. compileTesting )
} A build.gradle.kts
apply {
plugin( 'org.jetbrains.kotlin.jvm' )
plugin( 'org.jetbrains.kotlin.kapt' )
} java {
sourceCompatibility = JavaVersion. VERSION_1_8
targetCompatibility = JavaVersion. VERSION_1_8
}
dependencies { compile(deps. kotlin .stdLibJre8)
compile(deps. javaPoet )
compile(deps. autoCommon )
compileOnly(deps. autoService )
kapt(deps. autoService )
testCompile(deps. junit )
testCompile(deps. truth )
testCompile(deps. compileTesting )
} A build.gradle.kts
apply {
plugin( 'org.jetbrains.kotlin.jvm' )
plugin( 'org.jetbrains.kotlin.kapt' )
} java {
sourceCompatibility = JavaVersion. VERSION_1_8
targetCompatibility = JavaVersion. VERSION_1_8
}
dependencies { compile(deps. kotlin .stdLibJre8)
compile(deps. javaPoet )
compile(deps. autoCommon )
compileOnly(deps. autoService )
kapt(deps. autoService )
testCompile(deps. junit )
testCompile(deps. truth )
testCompile(deps. compileTesting )
} A build.gradle.kts
apply {
plugin( 'org.jetbrains.kotlin.jvm' )
plugin( 'org.jetbrains.kotlin.kapt' )
} java {
sourceCompatibility = JavaVersion. VERSION_1_8
targetCompatibility = JavaVersion. VERSION_1_8
}
dependencies { compile(deps. kotlin .stdLibJre8)
compile(deps. javaPoet )
compile(deps. autoCommon )
compileOnly(deps. autoService )
kapt(deps. autoService )
testCompile(deps. junit )
testCompile(deps. truth )
testCompile(deps. compileTesting )
} A build.gradle.kts
apply {
plugin( 'org.jetbrains.kotlin.jvm' )
plugin( 'org.jetbrains.kotlin.kapt' )
} java {
sourceCompatibility = JavaVersion. VERSION_1_8
targetCompatibility = JavaVersion. VERSION_1_8
}
dependencies { compile(deps. kotlin .stdLibJre8)
compile(deps. javaPoet )
compile(deps. autoCommon )
compileOnly(deps. autoService )
kapt(deps. autoService )
testCompile(deps. junit )
testCompile(deps. truth )
testCompile(deps. compileTesting )
} A build.gradle.kts
Plugin Author Buildscript Author App Developer
Plugin Author
Buildscript Author
App Developer
class My Plugin : Plugin<Project> {
override fun apply(project: Project) {
// ...
} B
} A
import org.gradle.kotlin.dsl.* class My Plugin : Plugin<Project> {
override fun apply(project: Project) {
// ...
} B
} A
kotlin-stdlib *.java *.kt kotlinc javac
kotlin-stdlib *.java *.kt kotlinc javac
apply plugin : 'your-gradle-plugin'
jakewharton jakewharton jakewharton twitter.com/ github.com/ .com A Builder's Intro to Kotlin
