Kotlin – the future of android

Kotlin – The Future of Android
DJ RAUSCH
ANDROID ENGINEER @ MOKRIYA

Kotlin – The Future of Android
What is Kotlin?
◦ Kotlin is a statically typed JVM language developed by Jetbrains. Jetbrains also develops IntelliJ IDEA,
which Android Studio is based off of.
◦ Kotlin compiles to Java bytecode, so it runs everywhere Java does.
◦ Kotlin has first class Java interoperability
◦ Use Java classes in Kotlin
◦ Use Kotlin classes in Java

Variable Comparison
JAVA KOTLIN
val type: Int
val color = 1
var size: Int
var foo = 20
final int type;
final int color = 1;
int size = 0;
int foo = 20;

Null Comparison
JAVA KOTLIN
String person = null;
if (person != null) {
int length = person.length();
}
var person: String? = null
var personNonNull: String = ""
var length = person?.length
var lengthNonNull = personNonNull.length

Strings
JAVA
String firstName = "DJ";
String lastName = "Rausch";
String welcome = "Hi " + firstName
+ " " + lastName;
String nameLength = "You name is “
+ (firstName.length() +
lastName.length())
+ " letters";
KOTLIN
val firstName = "DJ"
val lastName = "Rausch"
val welcome = "Hello $firstName
$lastName"
val nameLength = "Your name is
${firstName.length +
lastName.length}
letters"

Switch
JAVA KOTLIN
String gradeLetter = "";
int grade = 92;
switch (grade) {
case 0:
gradeLetter = "F";
break;
//...
case 90:
gradeLetter = "A";
break;
}
var grade = 92
var gradeLetter = when(grade){
in 0..59->"f"
in 60..69->"d"
in 70..79->"c"
in 80..89->"b"
in 90..100->"a"
else -> "N/A"
}

Loops
JAVA KOTLIN
for(int i = 0; i<10; i++){}
for(int i = 0; i<10; i+=2){}
for(String name:names){}
for (i in 0..9) {}
for (i in 0..9 step 2){}
for(name in names){}

Collections
JAVA KOTLIN
List<Integer> numbers
= Arrays.asList(1, 2, 3);
final Map<Integer, String> map
= new HashMap<>();
map.put(1, "One");
map.put(2, "Two");
map.put(3, "Three");
val numbers = listOf(1, 2, 3)
var map = mapOf(
1 to "One",
2 to "Two",
3 to "Three")

Collections Continued
JAVA KOTLIN
for (int number : numbers) {
System.out.println(number);
}
for (int number : numbers) {
if (number > 5) {
System.out.println(number);
}
}
numbers.forEach {
println(it)
}
numbers.filter { it > 5 }
.forEach { println(it) }

Enums
JAVA KOTLIN
public enum Size {
XS(1),S(2),M(3),L(4),XL(5);
private int sizeNumber;
private Size(int sizeNumber) {
this.sizeNumber =
sizeNumber;
}
public int getSizeNumber() {
return sizeNumber;
}
}
enum class Size(val sizeNumber: Int){
XS(1),S(2),M(3),L(4),XL(5)
}

Casting and Type Checking
JAVA KOTLIN
Object obj = "";
if(obj instanceof String){}
if(!(obj instanceof String)){}
String s = (String) obj;
val obj = ""
if (obj is String) { }
if (obj !is String) { }
val s = obj as String
val s1 = obj

Data Class
data class Color(val name:String, val hex: String)
val c = Color("Blue","#000088")
val hexColor = c.hex

Elvis Operator
var name: String? = null
val length = name?.length ?: 0

Extensions
fun Int.asMoney(): String {
return "$$this"
}
val money = 100.asMoney()

Infix Functions
infix fun Int.times(x: Int): Int {
return this * x;
}
val result = 2 times 3

Destructing Declarations
val c = Color("Blue", "#000088")
val (name, hex) = c
println(name) //Prints Blue
println(hex) //Prints #000088

Lazy
val name: String by lazy {
"DJ Rausch"
}

Coroutines
val deferred = (1..1000000).map { n ->
async(CommonPool) {
delay(1000)
n
}
}
runBlocking {
val sum = deferred.sumBy { it.await() }
println(sum)
}
https://kotlinlang.org/docs/tutorials/coroutines-basic-jvm.html

Android Extensions
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_kotlin.*
class KotlinActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_kotlin)
kt_hello_text_view.text = "Hello World!"
}
}

Android Extensions Continued
((TextView)this._$_findCachedViewById(id.kt_hello_text_view)).setText((CharSequence)"Hello World!");
public View _$_findCachedViewById(int var1) {
if(this._$_findViewCache == null) {
this._$_findViewCache = new HashMap();
}
View var2 = (View)this._$_findViewCache.get(Integer.valueOf(var1));
if(var2 == null) {
var2 = this.findViewById(var1);
this._$_findViewCache.put(Integer.valueOf(var1), var2);
}
return var2;
}

Anko
Anko is a Kotlin library which makes Android application development faster and easier. It makes
your code clean and easy to read, and lets you forget about rough edges of the Android SDK for
Java.
Anko consists of several parts:
Anko Commons: a lightweight library full of helpers for intents, dialogs, logging and so on;
Anko Layouts: a fast and type-safe way to write dynamic Android layouts;
Anko SQLite: a query DSL and parser collection for Android SQLite;
Anko Coroutines: utilities based on the kotlinx.coroutines library.

Anko - Intents
startActivity<MainActivity>()
startActivity<MainActivity>("id" to 1)

Anko – Toasts
toast("Hello ${name.text}")
toast(R.string.app_name)
longToast("LOOOONNNNGGGGG")

Anko – Dialogs
alert("Hello ${name.text}","Are you awesome?"){
yesButton {
toast("Well duh")
}
noButton {
toast("Well at least DJ is awesome!")
}
}

Anko – Progress Dialog
val dialog = progressDialog(message = "Please wait a bit…", title = "Fetching data")
indeterminateProgressDialog(message = "Loading something...", title = "LOADING")

Anko – Selector
val teams = listOf("University of Arizona", "Oregon", "ASU", "UCLA")
selector("Who won the Pac 12 Basketball Tournament in 2017?", teams, { _, i ->
//Do something
})

Anko – Layouts
class AnkoActivityUI : AnkoComponent<AnkoActivity> {
override fun createView(ui: AnkoContext<AnkoActivity>) = ui.apply {
verticalLayout {
padding = dip(20)
val name = editText()
button("Say Hello (Toast)") {
onClick {
toast("Hello ${name.text}")
}
}
}
}
}

Anko – Layouts Continued
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
AnkoActivityUI().setContentView(this)
}

Anko – Sqlite
fun getUsers(db: ManagedSQLiteOpenHelper): List<User> = db.use {
db.select("Users")
.whereSimple("family_name = ?", "Rausch")
.doExec()
.parseList(UserParser)
}

Java Kotlin Interoperability
For the most part, it just works!

Java in Kotlin
public class JavaObject {
private String name;
private String otherName;
public JavaObject(String name, String otherName) {
this.name = name;
this.otherName = otherName;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getOtherName() {
return otherName;
}
public void setOtherName(String otherName) {
this.otherName = otherName;
}
}

Java in Kotlin Continued
val javaObject = JavaObject("Hello", "World")
println(javaObject.name)
println(javaObject.otherName)

Kotlin in Java
data class KotlinObject(var name: String, var otherName: String)

Kotlin in Java Continued
KotlinObject kotlinObject = new KotlinObject("Hello", "World");
System.out.println(kotlinObject.getName());
System.out.println(kotlinObject.getOtherName());

Moving to Kotlin
•Very simple moving to Kotlin
•Android Studio can convert files for you
• You may need to fix a few errors it creates.

Kotlin EVERYWHERE
•Android
•Server
•Javascript
•Native

Kotlin Server (Ktor)
fun main(args: Array<String>) {
embeddedServer(Netty, 8080) {
routing {
get("/") {
call.respondText("Hello, World!", ContentType.Text.Html)
}
}
}.start(wait = true)
}

Kotlin Javascript
fun main(args: Array<String>) {
val message = "Hello JavaScript!"
println(message)
}

Kotlin Javascript Continued
if (typeof kotlin === 'undefined') {
throw new Error("Error loading module 'JSExample_main'. Its dependency 'kotlin' was not found. Please, check whether 'kotlin' is loaded prior to 'JSExample_main'.");
}
var JSExample_main = function (_, Kotlin) {
'use strict';
var println = Kotlin.kotlin.io.println_s8jyv4$;
function main(args) {
var message = 'Hello JavaScript!';
println(message);
}
_.main_kand9s$ = main;
main([]);
Kotlin.defineModule('JSExample_main', _);
return _;
}(typeof JSExample_main === 'undefined' ? {} : JSExample_main, kotlin);

Kotlin Native
•Will eventually allow for Kotlin to run practically anywhere.
• iOS, embedded platforms, etc
•Still early days
• https://github.com/JetBrains/kotlin-native

Questions?
Slides will be on my website soon™
https://djraus.ch
djrausch

Kotlin – the future of android

Kotlin – the future of android

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