Life is great and everything will be OK, Kotlin is here

A presentation at Google I/O in May 2017 in Mountain View, CA, USA by Jake Wharton

+Christina Lee @RunChristinaRun +Jake Wharton @JakeWharton Kotlin is here Life is great and everything will be OK

MainActivity.java public class MainActivity extends
Activity {
@Override
protected void onCreate ( Bundle savedInstanceState ) {
super . onCreate ( savedInstanceState );
} 1
} 2

MainActivity.java public class MainActivity extends
Activity {
@Override
protected void onCreate ( Bundle savedInstanceState ) {
super . onCreate ( savedInstanceState );
} 1
} 2

MainActivity.java public class MainActivity extends
Activity {
@Override
protected void onCreate ( Bundle savedInstanceState ) {
super . onCreate ( savedInstanceState );
} 1
} 2

MainActivity.java public class MainActivity extends
Activity {
@Override
protected void onCreate (@Nullable Bundle savedInstanceState ) {
super . onCreate ( savedInstanceState );
} 1
} 2
@Nullable

MainActivity.java public class MainActivity extends
Activity {
@Override
protected void onCreate (@Nullable Bundle savedInstanceState ) {
super . onCreate ( savedInstanceState );
} 1
} 2

MainActivity.kt class MainActivity :
Activity () {
override fun onCreate ( savedInstanceState: Bundle ? ) {
super . onCreate ( savedInstanceState ) } 1
} 2

MainActivity.kt class MainActivity :
Activity () {
override fun onCreate ( savedInstanceState: Bundle ? ) {
super . onCreate ( savedInstanceState ) } 1
} 2

MainActivity.kt class MainActivity :
Activity () {
override fun onCreate ( savedInstanceState: Bundle ? ) {
super . onCreate ( savedInstanceState ) } 1
} 2

TextView.java public float getAlpha () {
// Retrieve value...
}

TextView.java public float getAlpha () {
// Retrieve value...
}
public void setAlpha ( float alpha ) {
// Set value...
}

TextView.java public float getAlpha () {
// Retrieve value...
}
public void setAlpha ( float alpha ) {
// Set value...
} TextView tv
// ...
Log . d ( "MainActivity" ,
"Alpha: "
tv . getAlpha ());
tv . setAlpha ( 0f ); MainActivity.java

TextView.java public float getAlpha () {
// Retrieve value...
}
public void setAlpha ( float alpha ) {
// Set value...
} MainActivity.kt val tv
// ...
Log . d ( "MainActivity" ,
"Alpha: "
tv . alpha )
tv . alpha
0f

TextView.java public float getAlpha () {
// Retrieve value...
} 1
public void setAlpha ( float alpha ) {
// Set value...
} 2
MainActivity.kt val tv
// ...
Log . d ( "MainActivity" ,
"Alpha: "
tv . alpha )
tv . alpha
0f

TextView.java public float getAlpha () {
// Retrieve value...
} 1
public void setAlpha ( float alpha ) {
// Set value...
} 2
MainActivity.kt val tv
// ...
Log . d ( "MainActivity" ,
"Alpha: "
tv . alpha )
tv . alpha
0f

TextView.java public float getAlpha () {
// Retrieve value...
} 1
public void setAlpha ( float alpha ) {
// Set value...
} 2
MainActivity.kt val tv
// ...
Log . d ( "MainActivity" ,
"Alpha: "
tv . alpha )
tv . alpha
0f

MainActivity.java LinearLayout views
= // ...
for ( int i = 0 ; i < views . getChildCount ();
i ++ ) {
View view
= views . getChildAt ( i ); // TODO do something with view
}

MainActivity.kt val views = // ... for ( index in 0 until views . childCount ) {
val view
views . getChildAt ( index )
// TODO do something with view
}

MainActivity.kt val views = // ... for ( index in 0 until views . childCount ) {
val view
views . getChildAt ( index )
// TODO do something with view
} 1

MainActivity.kt val views = // ... for ( index in 0 until views . childCount ) {
val view
views . getChildAt ( index )
// TODO do something with view
} 1

MainActivity.kt val views = // ... for ( index in 0 until views . childCount ) {
val view
views . getChildAt ( index )
// TODO do something with view
}

MainActivity.kt val views = // ... for ( index in 0 until views . childCount ) { Z
val view
views . getChildAt ( index )
// TODO do something with view
} 1 ViewGroups.kt fun ViewGroup . forEach ( action: ( View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( getChildAt ( index )) } 2
} 3 .
Each
->

MainActivity.kt val views = // ... views . forEach { Z view
->
// TODO do something with view
} 1
ViewGroups.kt fun ViewGroup . forEach ( action: ( View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( getChildAt ( index )) } 2
} 3 val = views.getChildAt(i)

MainActivity.kt val views = // ... views . forEach { Z view
->
// TODO do something with view
} 1
ViewGroups.kt fun ViewGroup . forEach ( action: ( View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( getChildAt ( index )) } 2
} 3

MainActivity.kt val views = // ... views . forEach { Z view
->
// TODO do something with view
} 1
ViewGroups.kt fun ViewGroup . forEach ( action: ( View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( getChildAt ( index )) } 2
} 3

MainActivity.kt val views = // ... views . forEach { Z view
->
// TODO do something with view
} 1
ViewGroups.kt fun ViewGroup . forEach ( action: ( View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( getChildAt ( index )) } 2
} 3

MainActivity.kt val views = // ... views . forEach { Z view
->
// TODO do something with view
} 1
ViewGroups.kt fun ViewGroup . forEach ( action: ( View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( getChildAt ( index )) } 2
} 3

MainActivity.kt val views = // ... views . forEach { Z view
->
// TODO do something with view
} 1
ViewGroups.kt inline fun ViewGroup . forEach ( action: ( View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( getChildAt ( index )) } 2
} 3 inline

MainActivity.kt val views = // ... views . forEach { Z view
->
// TODO do something with view
} 1
ViewGroups.kt inline fun ViewGroup . forEach ( action: ( View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( getChildAt ( index )) } 2
} 3

MainActivity.kt val views = // ... views . forEach { Z view
-> /* ... */ } 1 views . forEachIndexed {
index , view
-> /* ... */ } 1
ViewGroups.kt inline fun ViewGroup . forEach ( action: ( View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( getChildAt ( index )) } 2
} 3 inline fun ViewGroup . forEachIndexed ( action: ( Int , View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( index , getChildAt ( index )) } } // TODO do something with view

MainActivity.kt val views = // ... views . forEach { Z view
-> /* ... */ } 1 views . forEachIndexed {
index , view
-> /* ... */ } 1
ViewGroups.kt inline fun ViewGroup . forEach ( action: ( View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( getChildAt ( index )) } 2
} 3 inline fun ViewGroup . forEachIndexed ( action: ( Int , View ) -> Unit ) {
for ( index in 0 until childCount ) {
action ( index , getChildAt ( index )) } } // TODO do something with view

MainActivity.kt val views = // ... // TODO do something with view ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )

MainActivity.kt val views = // ...
val first
views [ 0 ]
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index ) // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ]
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index ) // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ]
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index ) // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= first
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child ) // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= first
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child ) // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= first views += first
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child ) // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= first views += first
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child ) // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= first views += first if ( first in views ) doSomething ()
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1 // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= first views += first if ( first in views ) doSomething ()
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1 // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= first views += first if ( first in views ) doSomething ()
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1 // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= first views += first if ( first in views ) doSomething ()
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1 // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= fir st views += fi rst if ( first in views ) doSomething ()
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1 // TODO do something with view

MainActivity.kt val views = // ...
val first
views.get ( 0 ) views . minusAssign ( first )
views . plusAssign ( first )
if ( views . contains ( first )) doSomething ()
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1 // TODO do something with view
in

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= fir st views += fi rst if ( first in views ) doSomething ()
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1 // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= fir st views += fi rst if ( first in views ) doSomething () Log . d ( "MainActivity" , "View count: ${ views . size } " )
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1
val ViewGroup . size : Int
get () = childCount // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= fir st views += fi rst if ( first in views ) doSomething () Log . d ( "MainActivity" , "View count: ${ views . size } " )
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1
val ViewGroup . size : Int
get () = childCount // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= fir st views += fi rst if ( first in views ) doSomething () Log . d ( "MainActivity" , "View count: ${ views . size } " )
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1
val ViewGroup . size : Int
get () = childCount // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= fir st views += fi rst if ( first in views ) doSomething () Log . d ( "MainActivity" , "View count: ${ views . size } " )
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1
val ViewGroup . size : Int
get () = childCount // TODO do something with view

MainActivity.kt val views = // ...
val first
views [ 0 ] views -= fir st views += fi rst if ( first in views ) doSomething () Log . d ( "MainActivity" , "View count: ${ views . size } " )
ViewGroups.kt operator fun ViewGroup . get ( index: Int ) : View ?
getChildAt ( index )
operator fun ViewGroup . minusAssign ( child: View ) = removeView ( child )
operator fun ViewGroup . plusAssign ( child: View ) = addView ( child )
operator fun ViewGroup . contains ( child: View ) = indexOfChild ( child ) != - 1
val ViewGroup . size : Int
get () = childCount // TODO do something with view

MainActivity.kt val views = // ... // TODO do something with view ViewGroups.kt fun ViewGroup . children () = object : Iterable < View
{
override fun iterator () = object : Iterator < View
{
var index
= 0
override fun hasNext () = index
< childCount
override fun next () = getChildAt ( index ++) } }

MainActivity.kt val views = // ...
for ( view
in views . children ()) { // TODO do something with view
} 1
ViewGroups.kt fun ViewGroup . children () = object : Iterable < View
{
override fun iterator () = object : Iterator < View
{
var index
= 0
override fun hasNext () = index
< childCount
override fun next () = getChildAt ( index ++) } 2
} 3 // TODO do something with view

MainActivity.kt val views = // ...
for ( view
in views . children ()) { // TODO do something with view
} 1
val visibleHeight
views . children () . filter { it . visibility
View . VISIBLE
}
. sumBy { it . measuredHeight }
ViewGroups.kt fun ViewGroup . children () = object : Iterable < View
{
override fun iterator () = object : Iterator < View
{
var index
= 0
override fun hasNext () = index
< childCount
override fun next () = getChildAt ( index ++) } 2
} 3 // TODO do something with view

MainActivity.kt val views = // ...
for ( view
in views . children ()) { // TODO do something with view
}
val visibleHeight
views . children () . filter { it . visibility
View . VISIBLE
}
. sumBy { it . measuredHeight }
ViewGroups.kt fun ViewGroup . children () = object : Iterable < View
{
override fun iterator () = object : Iterator < View
{
var index
= 0
override fun hasNext () = index
< childCount
override fun next () = getChildAt ( index ++) } } // TODO do something with view

MainActivity.java Trace . beginSection ( sectionName );
expensiveCalculation ();
Trace . endSection () ;

MainActivity.java Trace . beginSection ( sectionName );
expensiveCalculation ();
Trace . endSection () ; Traces.kt inline fun
trace ( sectionName: String , body: () -> Unit )
{
Trace . beginSection ( sectionName )
try {
body () } 2 finally {
Trace . endSection () } 3
} 4

Traces.kt inline fun
trace ( sectionName: String , body: () -> Unit )
{ Z
Trace . beginSection ( sectionName )
try {
body () } 2 finally {
Trace . endSection () } 3
} 4 MainActivity.kt trace ( "foo" ) {
expensiveCalculation () } 1

Traces.kt inline fun < T
trace ( sectionName: String , body: () -> T ) :
T
{ Z
Trace . beginSection ( sectionName )
try {
return body () } 2 finally {
Trace . endSection () } 3
} 4
Unit MainActivity.kt trace ( "foo" ) {
expensiveCalculation () } 1
< T
T
T
return

Traces.kt inline fun < T
trace ( sectionName: String , body: () -> T ) :
T
{ Z
Trace . beginSection ( sectionName )
try {
return body () } 2 finally {
Trace . endSection () } 3
} 4 MainActivity.kt val result
trace ( "foo" ) {
expensiveCalculation () } 1 val result
< T
T
T
return

Traces.kt inline fun < T
trace ( sectionName: String , body: () -> T ) :
T
{ Z
Trace . beginSection ( sectionName )
try {
return body () } 2 finally {
Trace . endSection () } 3
} 4 MainActivity.kt val result
trace ( "foo" ) {
expensiveCalculation () } 1

MainActivity.java SQLiteDatabase db = // ... db . beginTransaction (); try {
db . delete ( "users" ,
"first_name = ?" ,
new
String [] { "jake" }); } finally {
db . endTransaction (); } 1

MainActivity.java SQLiteDatabase db = // ... db . beginTransaction (); try {
db . delete ( "users" ,
"first_name = ?" ,
new
String [] { "jake" });
db . setTransactionSuccessful (); } finally {
db . endTransaction (); } 1

SQLiteDatabase db = // ... db . beginTransaction (); try {
db . delete ( "users" ,
"first_name = ?" ,
new
String [] { "jake" });
db . setTransactionSuccessful (); } finally {
db . endTransaction (); } 1 Databases .kt inline fun SQLiteDatabase . transaction ( body: () -> Unit ) {
beginTransaction ()
try {
body ()
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1

MainActivity.kt val db = // ... db . transaction
{ 4
db . delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: () -> Unit ) {
beginTransaction ()
try {
body () X
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1 SQLiteDatabase
db.beginTransaction(); try new String[] { } db.setTransactionSuccessful(); finally { db.endTransaction(); }1

MainActivity.kt val db = // ... db . transaction
{ 4
db . delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: () -> Unit ) {
beginTransaction ()
try {
body () X
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1

MainActivity.kt val db = // ... db . transaction
{ 4
db . delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: () -> Unit ) {
beginTransaction ()
try {
body () X
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1

MainActivity.kt val db = // ... db . transaction
{ 4
db . delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: ( SQLiteDatabase ) -> Unit ) {
beginTransaction ()
try {
body () X
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1
SQLiteDatabase

MainActivity.kt val db = // ... db . transaction
{ 4
db . delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: ( SQLiteDatabase ) -> Unit ) {
beginTransaction ()
try {
body ( this ) X
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1
SQLiteDatabase
body ( this ) X

MainActivity.kt val db = // ... db . transaction
{ 4
it . delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: ( SQLiteDatabase ) -> Unit ) {
beginTransaction ()
try {
body ( this )
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1
it . delete
SQLiteDatabase
body ( this ) X

MainActivity.kt val db = // ... db . transaction
{ 4
it . delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: ( SQLiteDatabase ) -> Unit ) {
beginTransaction ()
try {
body ( this ) F
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1

MainActivity.kt val db = // ... db . transaction
{ 4
it . delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: ( SQLiteDatabase ) -> Unit ) {
beginTransaction ()
try {
body ( this ) F
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1

MainActivity.kt val db = // ... db . transaction
{ 4
it . delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: ( SQLiteDatabase ) -> Unit ) {
beginTransaction ()
try {
body ( this ) F
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1

MainActivity.kt val db = // ... db . transaction
{ 4
it . delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: SQLiteDatabase .() -> Unit ) {
beginTransaction ()
try {
body ( this ) F
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1
SQLiteDatabase .() -> Unit

MainActivity.kt val db = // ... db . transaction
{ 4
it . delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: SQLiteDatabase .() -> Unit ) {
beginTransaction ()
try {
body ()
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1
SQLiteDatabase .() -> Unit
body
() F

it. MainActivity.kt val db = // ... db . transaction
{ 4
delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" ) ) } 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: SQLiteDatabase .() -> Unit ) {
beginTransaction ()
try {
body ()
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1 delete
SQLiteDatabase .() -> Unit
body
() F

MainActivity.kt val db = // ... db . transaction
{ 4
delete ( "users" ,
"first_name = ?" , arrayOf ( "jake" )) G
} 3
Databases .kt inline fun SQLiteDatabase . transaction ( body: SQLiteDatabase .() -> Unit ) {
beginTransaction ()
try {
body ()
setTransactionSuccessful () } finally {
endTransaction () } 2
} 1 1

MainActivity.kt = // ... "jake" Databases.kt inline fun SQLiteDatabase.transaction(body: SQLiteDatabase.() -> Unit) { beginTransaction() try { body() setTransactionSuccessful() } finally { endTransaction() }2
}1 1 class UserPersistence ( private val db: SQLiteDatabase ) {
fun deleteByFirstName ( name: String ) {
db . transaction {
delete ( "users" , "first_name = ?" , arrayOf ( name )) G
} 3
} } UserPersistence.kt

MainActivity.kt = // ... "jake" Databases.kt inline fun SQLiteDatabase.transaction(body: SQLiteDatabase.() -> Unit) { beginTransaction() try { body() setTransactionSuccessful() } finally { endTransaction() }2
}1 1 class UserPersistence ( private val db: SQLiteDatabase ) {
fun deleteByFirstName ( name: String ) {
db . transaction {
delete ( "users" , "first_name = ?" , arrayOf ( name )) G
} 3
} } UserPersistence.kt

class UserPersistence ( private val db: SQLiteDatabase ) {
fun deleteByFirstName ( name: String ) {
db . transaction {
delete ( "users" , "first_name = ?" , arrayOf ( name )) G
} 3
} 2
} 1 UserPersistence.kt

class UserPersistence ( private val db: SQLiteDatabase ) {
private val
deleteByFirstName
db . compileStatement (
"DELETE FROM users WHERE first_name = ?" )
fun deleteByFirstName ( name: String ) {
db . transaction {
deleteByFirstName . bindString ( 1 , name )
deleteByFirstName . execute ()
} 3
} 2
} 1 UserPersistence.kt
delete(" ", " , arrayOf ( ))G

sssssssssssss class UserPersistence ( private val db: SQLiteDatabase ) {
private val
deleteByFirstName
db . compileStatement (
"DELETE FROM users WHERE first_name = ?" )
fun deleteByFirstName ( name: String ) {
db . transaction {
deleteByFirstName . bindString ( 1 , name )
deleteByFirstName . execute ()
} 3
} 2
} 1 UserPersistence.kt

sssssssssssss class UserPersistence ( private val db: SQLiteDatabase ) {
private val deleteByFirstName
by lazy {
db . compileStatement ( "DELETE FROM users WHERE first_name = ?" ) }
fun deleteByFirstName ( name: String ) {
db . transaction {
deleteByFirstName . bindString ( 1 , name )
deleteByFirstName . execute ()
} 3
} 2
} 1 UserPersistence.kt

sssssssssssss class UserPersistence ( private val db: SQLiteDatabase ) {
private val deleteByFirstName
by lazy {
db . compileStatement ( "DELETE FROM users WHERE first_name = ?" ) } X
fun deleteByFirstName ( name: String ) {
db . transaction {
deleteByFirstName . bindString ( 1 , name )
deleteByFirstName . execute ()
} 3
} 2
} 1 UserPersistence.kt

private val deleteByFirstName
by lazy {
db . compileStatement ( "DELETE FROM users WHERE first_name = ?" ) } X

private val deleteByFirstName
by lazy {
db . compileStatement ( "DELETE FROM users WHERE first_name = ?" ) } X private val name
by Delegates . observable ( "jane" ) { old , new , prop ->
println ( "Name changed from $ old to $ new " ) }

private val deleteByFirstName
by lazy {
db . compileStatement ( "DELETE FROM users WHERE first_name = ?" ) } X private val name
by Delegates . observable ( "jane" ) { old , new , prop ->
println ( "Name changed from $ old to $ new " ) }
private val address
by Delegates . notNull < String
()

private val deleteByFirstName
by lazy {
db . compileStatement ( "DELETE FROM users WHERE first_name = ?" ) } X private val name
by Delegates . observable ( "jane" ) { old , new , prop ->
println ( "Name changed from $ old to $ new " ) }
private val address
by Delegates . notNull < String
()
private val nameView
by bindView < TextView
( R . id . name )

private val deleteByFirstName
by lazy {
db . compileStatement ( "DELETE FROM users WHERE first_name = ?" ) } X private val name
by Delegates . observable ( "jane" ) { old , new , prop ->
println ( "Name changed from $ old to $ new " ) }
private val address
by Delegates . notNull < String
()
private val nameView
by bindView < TextView
( R . id . name )

class MyListener : TransitionListener {
override fun onTransitionEnd ( transition: Transition ) { }
override fun onTransitionResume ( transition: Transition ) { }
override fun onTransitionPause ( transition: Transition ) { }
override fun onTransitionCancel ( transition: Transition ) { }
override fun onTransitionStart ( transition: Transition ) { } Y
} X

class MyListener : TransitionListener {
override fun onTransitionStart ( transition: Transition ) { } Y
} X

class MyListener : TransitionListener {
override fun onTransitionStart ( transition: Transition ) { } Y
} X
object EmptyTransitionListener : TransitionListener {
override fun onTransitionEnd ( transition: Transition ) {}
override fun onTransitionResume ( transition: Transition ) {}
override fun onTransitionPause ( transition: Transition ) {}
override fun onTransitionCancel ( transition: Transition ) {}
override fun onTransitionStart ( transition: Transition ) {} }

class MyListener : TransitionListener {
override fun onTransitionStart ( transition: Transition ) { } Y
} X
object EmptyTransitionListener : TransitionListener {
override fun onTransitionEnd ( transition: Transition ) {}
override fun onTransitionResume ( transition: Transition ) {}
override fun onTransitionPause ( transition: Transition ) {}
override fun onTransitionCancel ( transition: Transition ) {}
override fun onTransitionStart ( transition: Transition ) {} }

class MyListener : TransitionListener { T
override fun onTransitionStart ( transition: Transition ) { } Y
} X
object EmptyTransitionListener : TransitionListener {
override fun onTransitionEnd ( transition: Transition ) {}
override fun onTransitionResume ( transition: Transition ) {}
override fun onTransitionPause ( transition: Transition ) {}
override fun onTransitionCancel ( transition: Transition ) {}
override fun onTransitionStart ( transition: Transition ) {} } G

class MyListener : TransitionListener by EmptyTransitionListener { T
override fun onTransitionStart ( transition: Transition ) { } Y
} X
object EmptyTransitionListener : TransitionListener {
override fun onTransitionEnd ( transition: Transition ) {}
override fun onTransitionResume ( transition: Transition ) {}
override fun onTransitionPause ( transition: Transition ) {}
override fun onTransitionCancel ( transition: Transition ) {}
override fun onTransitionStart ( transition: Transition ) {} } G

class MyListener : TransitionListener by EmptyTransitionListener { T
override fun onTransitionStart ( transition: Transition ) { } Y
} X
object EmptyTransitionListener : TransitionListener {
override fun onTransitionEnd ( transition: Transition ) {}
override fun onTransitionResume ( transition: Transition ) {}
override fun onTransitionPause ( transition: Transition ) {}
override fun onTransitionCancel ( transition: Transition ) {}
override fun onTransitionStart ( transition: Transition ) {} } G

class PaymentRobot {
fun amount ( value: Long ) { // TODO Espresso interactions
}
fun recipient ( value: String ) { // TODO Espresso interactions
}
fun send () { // TODO Espresso interactions
} } PaymentRobot.kt

@Test
fun sendMoney () {
PaymentRobot (). apply {
amount ( 4_00 )
recipient ( "foo@example.com" )
send ()
} } PaymentTest.kt

class PaymentRobot {
fun amount ( value: Long ) { // TODO Espresso interactions
}
fun recipient ( value: String ) { // TODO Espresso interactions
}
fun send () { // TODO Espresso interactions
} }
PaymentRobot.kt

class PaymentRobot {
fun amount ( value: Long ) { // TODO Espresso interactions
}
fun recipient ( value: String ) { // TODO Espresso interactions
}
fun send () { // TODO Espresso interactions
} }
PaymentRobot.kt fun payment ( body: PaymentRobot .() -> Unit ) = PaymentRobot (). apply ( body )

class PaymentRobot {
fun amount ( value: Long ) { // TODO Espresso interactions
}
fun recipient ( value: String ) { // TODO Espresso interactions
}
fun send () { // TODO Espresso interactions
} }
PaymentRobot.kt fun payment ( body: PaymentRobot .() -> Unit ) = PaymentRobot (). apply ( body )

@Test
fun sendMoney () {
PaymentRobot (). apply { T
amount ( 4_00 )
recipient ( "foo@example.com" )
send ()
} T
} G
PaymentTest.kt
p

@Test
fun sendMoney () {
payment { T
amount ( 4_00 )
recipient ( "foo@example.com" )
send ()
} T
} G
PaymentTest.kt

sealed class Payloads { } G

sealed class Payloads {
data class Favorite ( val favorited: Boolean ) : Payloads () } G

sealed class Payloads {
data class Favorite ( val favorited: Boolean ) : Payloads ()
data class Retweet ( val retweeted: Boolean ) : Payloads () } G

sealed class Payloads {
data class Favorite ( val favorited: Boolean ) : Payloads ()
data class Retweet ( val retweeted: Boolean ) : Payloads ()
data class CountUpdate (
val favorites: Long ,
val retweets: Long ,
val replies: Long ) : Payloads () } G

override fun onBindViewHolder ( holder: TweetViewHolder ,
position: Int , payloads: List < Any
) {
} 1

override fun onBindViewHolder ( holder: TweetViewHolder ,
position: Int , payloads: List < Any
) {
payloads . forEach {
} 2
} 1

override fun onBindViewHolder ( holder: TweetViewHolder ,
position: Int , payloads: List < Any
) {
payloads . forEach {
when ( it ) {
}
3
} 2
} 1

override fun onBindViewHolder ( holder: TweetViewHolder ,
position: Int , payloads: List < Any
) {
payloads . forEach {
when ( it ) {
is Favorite -> holder . favoriteIcon . isActivated
= it . favorited
}
3
} 2
} 1

override fun onBindViewHolder ( holder: TweetViewHolder ,
position: Int , payloads: List < Any
) {
payloads . forEach {
when ( it ) {
is Favorite -> holder . favoriteIcon . isActivated
= it . favorited
}
3
} 2
} 1

override fun onBindViewHolder ( holder: TweetViewHolder ,
position: Int , payloads: List < Any
) {
payloads . forEach {
when ( it ) {
is Favorite -> holder . favoriteIcon . isActivated
= it . favorited
}
3
} 2
} 1 sealed class Payloads {
data class Favorite ( val favorited: Boolean ) : Payloads ()
data class Retweet ( val retweeted: Boolean ) : Payloads ()
data class CountUpdate (
val favorites: Long ,
val retweets: Long ,
val replies: Long ) : Payloads () } G

override fun onBindViewHolder ( holder: TweetViewHolder ,
position: Int , payloads: List < Any
) {
payloads . forEach {
when ( it ) {
is Favorite -> holder . favoriteIcon . isActivated
= it . favorited
}
3
} 2
} 1

override fun onBindViewHolder ( holder: TweetViewHolder ,
position: Int , payloads: List < Any
) {
payloads . forEach {
when ( it ) {
is Favorite -> holder . favoriteIcon . isActivated
= it . favorited
is Retweet -> holder . retweetIcon . isActivated
= it . retweeted
}
3
} 2
} 1

override fun onBindViewHolder ( holder: TweetViewHolder ,
position: Int , payloads: List < Any
) {
payloads . forEach {
when ( it ) {
is Favorite -> holder . favoriteIcon . isActivated
= it . favorited
is Retweet -> holder . retweetIcon . isActivated
= it . retweeted
is CountUpdate -> {
holder . apply {
favoriteCount . text
= it . favorites . toString ()
retweetCount . text
= it . retweets . toString ()
replyCount . text
= it . replies . toString ()
} 5
} 4
}
3
} 2
} 1

It takes great salesmanship to convince a customer to buy something from you that isn't built or isn't finished.
Fred Wilson

Step 3 Step 2 Step 1

Step 1 Step 3 You Step 2

Step 3 Management Step 2 Step 1

Team Step 3 Step 2 Step 1

You Get excited.

Never doubt that a small group of thoughtful, committed citizens can change the world; indeed,   it's the only thing   that ever has.
Margaret Mead (Def. not talking about tech)

Be enthusiastic

Adoption is work. If you want it, you need to earn it.

Management Be persuasive.

I call it my billion- dollar mistake . Sir Charles Antony Richard Hoare

One of the most feared expressions in modern times is 'The computer is down.'
Norman Ralph Augustine

Jake Wharton
@JakeWharton Ty p e s y s t e m s a r e a f o r m o f t e s t s . I d e c l a r e a n e x p e c t e d
type and the tests (aka compiler) validates the actual ones. 6:43 PM - 11 Jan 2017 74 Follow 16

Team Do the work.

Ellen Shapiro
@designatednerd My style: “I’m the idiot who went down the rabbit hole first, and I’m here to tell you which path leads to fluffy bunnies vs. angry moles.” 14 Mar Ellen Shapiro
@designatednerd My favorite bit of any talk I give is talking about the dumb shit I did so the audience doesn’t do it. Makes the hair pulled out worth it. 4:56 PM - 14 Mar 2017 1 Follow

Define success

http://blog.danlew.net/

On-boarding should be a first class citizen

Show up

What’s next? Kotlin documentation and koans
https://kotlinlang.org/
Android Kotlin documentation
https://developer.android.com/kotlin/index.html
Kotlin In Action
Dimitry Jemerov, Svetlana Isakova

+Christina Lee @RunChristinaRun #KotlinIsHere Thank you!
+Jake Wharton @JakeWharton

Jake Wharton
@jakewharton

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Using Kotlin for Android development has grown in popularity over the past few years and is now officially supported by Google. If you are not already using Kotlin you might be wondering why and how to adopt it. In the first part of this talk, Jake will cover advancing the usage and design patterns of the language for Android development to solve larger problems. In the second part, Christina will share her experience using Kotlin in production, from mistakes to successes, and help you answer questions your team/company might ask about adopting it.

Presented with Christina Lee

Video