Presentation for Android Developers about why they should consider using Kotlin. Key features of the language are discussed in comparison with Java. #LanguageChoiceMatters http://blog.jimbaca.com

1. Jim Baca
@desertjim
http://blog.jimbaca.com
Kotlin
Carlsbad Caverns

2. AI Story Time

4. #LanguageChoiceMatters

5. Kotlin
• Nov 8, 2010
• JVM Language Summit
• Productive
• No Compatibility Compromises
• Compilation Speed
• Feb 14, 2016
• JS

6. My Favorite Things

7. Precap
• syntax
• null safety
• smart casting
• extension functions
• delegation
• sealed classes
• DSL

8. How
• Concise
• Convenient
• Focus

9. Color Legend
Java Kotlin

10. Basic Syntax
var a: Int = 1000
final Integer b = 500
Integer a = 1000
val b: Int = 500
boolean, float, int, char etc

11. a.toString();
Null
Integer a = null;
💥

12. a.toString();
Null
Integer a = null;
💥

13. Null Checks
var book: Book = null 🖥⚠
var book: Book? = null
var book: Book? = Book()

14. Safe Call Operator
book?.title
book?.getTitle(locale :String)

15. Null !!
val publisher: Publisher = book!!.publisher

16. !! Operator
val publisher: Publisher = book!!.publisher

17. Null && Safe Chaining
if(book != null && book.getPublisher() != null &&…){
…
}
book?.publisher?.address

18. let
var book: Book = …
book?.let {
toast(“Hello, ${it.authors}!”)
}

19. let
Hello,[Author(firstName=Jim,
lastName=Baca), Author(firstName=John,
lastName=Bekas)]

20. Elvis Operator
var address = book?.publisher?.address
var address = book?.publisher?.address ?:
"3300 N Interstate 35, Austin, TX"

21. Late Init
class MainActivity : AppCompatActivity() {
lateinit var book : Book
override fun onCreate(savedInstanceState: Bundle?)
{
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
book.edition
}
}
⚠ 💥
lateinit property book has not been initialized

22. Smart Casting

23. Reduced Casting

24. Smart Casting
if (x instanceof String) {
print(((String) x).length());
}
if (!(x instanceof String)) {
return;
}
print(((String) x).length());
if (x is String) {
print(x.length)
}
if (x !is String)
return
print(x.length)

25. Smart Casting
if (x !is String || x.length == 0) return
if (x is String && x.length > 0)
when (x) {
is Int -> print(x + 1)
is String -> print(x.length + 1)
is IntArray -> print(x.sum())
}

26. Nullable Casting
var first: Book? = current as? Book
(current as Book).let{
it.author
}

27. Fun
fun double(x: Int): Int {
return 2 * x
}
fun double(x: Int): Int = 2 * x
fun double(x: Int) = 2 * x

28. Optionals
fun add(x: Int, y: Int = 1, z: Int = 2): Int {
return x + y + z
}
add(5)
add(5, z = 5)

29. Syntax
fun logIt(tag:String, value: String?): Unit {
if (tag != null && value != null)
Log.e(tag, value)
else
Log.e(tag, "nothing")
}

30. Syntax
fun logIt(tag:String, value: String?){
if (tag != null && value != null)
Log.e(tag, value)
else
Log.e(tag, "nothing")
}

31. Interface
interface Book {
val author: String
val title: String
get() = “Wizard of Oz"
fun printAuthor() {
print(author)
}
}
class TechBook : Book {
override val author: String = "Howard Lee"
}

32. Interface Conflicts
interface A {
fun foo() { print("A") }
}
interface B {
fun foo() { print("B") }
fun bar() { print("bar") }
}
class D : A, B {
// foo?
}

33. Interface Conflicts
interface A {
fun foo() { print("A") }
}
interface B {
fun foo() { print("B") }
fun bar() { print("bar") }
}
class D : A, B {
override fun foo() {
super<A>.foo()
super<B>.foo()
}

34. Extension Functions
int verticalLineThickness = TypedValue.COMPLEX_UNIT_DIP;
DisplayMetrics metrics = context.getResources().getDisplayMetrics();
float lineWidth = TypedValue.applyDimension(type, value, metrics);
int fontTitleSize = TypedValue.COMPLEX_UNIT_SP;
float titleSize = TypedValue.applyDimension(type, value, metrics);
int fontSubtitleSize = TypedValue.COMPLEX_UNIT_SP;
float subtitleSize = TypedValue.applyDimension(type, value, metrics);

35. Extension Functions
fun View.applyDimension(
value: Float,
type : Int = TypedValue.COMPLEX_UNIT_DIP
): Float{
val metrics = getResources().getDisplayMetrics()
val resultPix = TypedValue.applyDimension(type, value, metrics)
return resultPix
}

36. Extension Functions
class CustomView : View {
constructor(context: Context?) : super(context){
initialize()
}
…
fun initialize(){
val verticalLineThickness = applyDimension(5f)
val horizontalLineThickness = applyDimension(10f)
val paddingBetweenItems = applyDimension(15f)
val fontTitleSize = applyDimension(32f, TypedValue.COMPLEX_UNIT_SP)
val subtitleSize = applyDimension(14f, TypedValue.COMPLEX_UNIT_SP)
}
}

37. Extension Functions
fun TextView.setTextSize(value: Float,
type: Int = TypedValue.COMPLEX_UNIT_SP):
Float {
val res = getResources()
val metrics = res.getDisplayMetrics()
val resultPix = TypedValue.applyDimension(
type, value, metrics)
return resultPix
}
public void setTextSize(int unit, float size)

38. Extension Functions
Conflicts
fun TextView.setTextSize(value: Float,
type: Int = TypedValue.COMPLEX_UNIT_SP):
Float {
val res = getResources()
val metrics = res.getDisplayMetrics()
val resultPix = TypedValue.applyDimension(
type, value, metrics)
return resultPix
}
setTextSize(15.8f)
public void setTextSize(float size)

39. Extension Functions
• operator fun <K, V> Map<K, V>.iterator():
Iterator<Map.Entry<K, V>> = entrySet().iterator()
• operator fun <K, V> Map.Entry<K,
V>.component1() = getKey()
• operator fun <K, V> Map.Entry<K,
V>.component2() = getValue()

40. Nullable Receiver
fun Any?.toString(): String {
if (this == null) return "null"
return toString()
}
V/Test: null
var book: Book? = null
Log.v("Test", book.toString())

41. Destructuring Declarations

42. Returning Multiple Items

43. Returning Multiple Items
for ((key, value) in map) {
// do something with the key and the value
}

44. Returning Multiple Items
val (authors, datePublished) = getBook()
val authors = book.component1()
val datePublished = book.component2()
componentN() 🔑 operator
data class 🎉

45. data class
data class Book(
var authors: ArrayList<Author>,
var publication: Date,
var title: String,
var publisher: Publisher,
var isbn: String,
var asin: String,
var bookCover: Uri
)
public class Book {
ArrayList<Author> authors;
Date publication;
String title;
Publisher publisher;
String isbn;
String asin;
Uri bookCover;
public ArrayList<Author> getAuthors() {
return authors;
}
public void setAuthors(
ArrayList<Author> authors) {
this.authors = authors;
}
public Date getPublication() {
return publication;
}
. . .
BARF

46. Sealed Classes
V. Enums
• Restricted Type
• Multiple Instances
• State

47. Sealed Classes
sealed class Book {
class Ebook(val site: String) : Book()
class Paper(val edition: String) : Book()
object NotABook : Book()
}
fun meta(book: Book): String? = when(book) {
is Book.Ebook -> book.site
is Book.Paper -> book.edition
Book.NotABook -> null
}

48. Inheritance Hell

49. Inheritance Hell
Fragment
Web Socket
Fragment
List Fragment

50. Inheritance Hell
Fragment
Web Socket
Fragment
List Fragment
Detail
Fragment
RxLifeCycle❤
Fragment

51. Inheritance Hell
Fragment
Web Socket
Fragment
List Fragment
Detail
Fragment
RxLifeCycle
Fragment

52. Inheritance Hell
Fragment
Web Socket
Fragment
List Fragment
Detail
Fragment
RxLifeCycle
Fragment

53. Inheritance Hell
Fragment
Web Socket
Fragment
List Fragment
Detail
Fragment
RxLifeCycle
Fragment
Modified List
Fragment

54. Inheritance Hell
Fragment
Web Socket
Fragment
List Fragment
Detail
Fragment
RxLifeCycle
Fragment
Modified List
Fragment

55. Inheritance Heaven
Fragment
List Fragment
Web Socket
Shared List
Logic
Detail
Fragment
RxLifeCycle
Fragment
Modified List
Fragment

56. Class Delegation
interface Base {
void print()
}
class BaseImpl extends Base {
int x;
public BaseImpl(int x){
this.x = x;
}
@Override
void print() {
print(x);
}
}
class Derived extends Base{
Base delegate;
@Override
void print(){
delegate.print();
}
void setDelegate(Base b){
delegate = b;
}
}
BaseImpl imp = new BaseImp(10);
Derived derived = new Derived();
derived.setDelegate(imp);
derived.print();

57. Class Delegation
interface Base {
fun print()
}
class BaseImpl(val x: Int) : Base {
override fun print() { print(x) }
}
class Derived(b: Base) : Base by b
val b = BaseImpl(10)
Derived(b).print()

58. Delegated Properties
class Example {
var p: String by Delegate()
}

59. Delegated Properties
class Delegate {
operator fun getValue(thisRef: Any?, property: KProperty<*>): String {
return "$thisRef, delegated '${property.name}' to me!"
}
operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {
println("$value = '${property.name} in $thisRef.'")
}
}

60. Delegated Properties
val e = Example()
println(e.p)
Example@33a17727, delegated ‘p’ to me!
e.p = "NEW"
NEW = ‘p’ in Example@33a17727

61. Anko

62. DSL
val activity = this
val layout = LinearLayout(activity)
layout.orientation = LinearLayout.VERTICAL
val name = EditText(activity)
val button = Button(activity)
button.text = "Say Hello"
button.setOnClickListener {
Toast.makeText(activity, "Hello, ${name.text}!",
Toast.LENGTH_SHORT).show()
}
layout.addView(name)
layout.addView(button)

63. DSL
verticalLayout {
val name = editText()
button("Say Hello") {
onClick { toast("Hello, ${name.text}!") }
}
}

64. DSL
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/
apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<EditText
android:id="@+id/name"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
<Button
android:id="@+id/clicked"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</LinearLayout>

65. DSL
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
verticalLayout {
val name = editText()
button("Say Hello") {
onClick { toast("Hello, ${name.text}!") }
}
}
}
}
setContentView 👀

66. Kotlin Setup
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"

67. Kotlin Setup
apply plugin: 'kotlin-android'
compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"

68. Resources
• ⌥Ctrl ⇧ Shift ⌘ Cmd K
• blog.jetbrains.com/kotlin/2016/03/kotlins-android-
roadmap
• github.com/kotlin/kotlin-koans
• try.kotlinlang.org
• github.com/antoniolg/bandhook-kotlin
• github.com/jetbrains/kotlin-examples

69. FAQ
• Compatibility
• Support
• 20 K

70. The Numbers
Proguard Java Kotlin
File Size 726 KB 778 KB
Dex Count 4894 4894
Java Kotlin
File Size 1.2 MB 1.6 MB
Dex Count 16174 23107

71. Recap
• syntax
• null safety
• smart casting
• extension functions
• delegation
• sealed classes
• DSL

72. #LanguageChoiceMatters
@AustinDroids @Evernote🏢@HotSchedules🍕
@desertjim
blog.jimbaca.com