This document introduces Kotlin, a statically typed programming language that runs on the Java Virtual Machine (JVM). It summarizes Kotlin's key features like concise syntax, null safety, interoperability with Java, and extension functions. The document also provides examples of Kotlin code for functions, properties, lambdas, and higher-order functions. It describes how Kotlin can be used for Android development and introduces libraries like Anko that simplify common Android tasks.

1. Kotlin in Action
A concise way to code Android Projects
in a smarter way
© 2016

2. What is Kotlin?
...it’s just another language…
● Created by Jetbrains
● Statically typed
● Lightweight
● Running on JVM

3. Old fashion Android Coding
● Android supports only Java6(ish)
● The verbosity of Java is annoying (i.e. a lot of boilerplate code)
● The Billion Dollar Mistake (aka Null Reference)

4. Why Kotlin?
● Concise: Reduce the boilerplate code, no ceremonies, no decorations
● Safe: It’s a Null Safety language
● Versatile: Write Android, Front end and Server Side applications
● Interoperable: Write Kotlin and Java code in the same project

5. Kotlin Language

6. The Language
fun getAvg(a: Int, b: Int): Int {
return (a + b) / 2
}
fun getAvg(a: Int, b: Int) = (a + b) / 2
val number: Int = 0
val stringArray = ArrayList<String>()
var average: Float? = null

7. Extension Functions
Simply way to extend a class adding new functions
fun Context.toast(message: CharSequence, duration: Int = Toast.LENGTH_SHORT) {
Toast.makeText(this, message, duration).show()
}
…
toast("Hello Folks!")

8. Extension Functions
fun MutableList<Int>.swap(index1: Int, index2: Int) {
val tmp = this[index1] // 'this' corresponds to the list
this[index1] = this[index2]
this[index2] = tmp
}
fun <T> MutableList<T>.swap(index1: Int, index2: Int) {
val tmp = this[index1] // 'this' corresponds to the list
this[index1] = this[index2]
this[index2] = tmp
}

9. Extension Functions
fun ImageView.loadImage(url: String) {
Glide.with(context)
.load(url)
.diskCacheStrategy(DiskCacheStrategy.ALL)
.fitCenter()
.into(this)
}

10. Lambda Expression Syntax
val sum : (Int, Int) -> Int = {x: Int, y: Int -> x + y}
val sum = { x: Int, y: Int -> x + y }
val notEmpty: (String) -> Boolean = { !it.isEmpty() }
val notEmpty = { it: String -> !it.isEmpty() }

11. Higher-Order Functions and Lambdas
A function that takes functions as parameters, or returns a function
fun getId(id: Int, func: (Int) -> String): String {
return func(id)
}
val hereMyID = getId(101478, { x -> "Here My Id: $x" })

12. Lazy Initialization
var mySdk : Sdk? = null
mySdk = Sdk()
Sdk mySdk = null;
mySdk = new Sdk();
Java Kotlin
lateinit var mySdk : Sdk
mySdk = Sdk()

13. Lazy Initialization
Kotlin
class JavaClass {
Sdk mySdk;
final Sdk getSdk() {
if (mySdk == null) {
mySdk = new Sdk();
}
return mySdk;
}
}
val mySdk : Sdk by lazy { getSdk() }
protected fun getSdk() = Sdk()
Java
val mySdk : Sdk by lazy { Sdk() }

14. Kotlin Android Extensions Library
Java:
recyclerView = (RecyclerView)findViewById(R.id.recycler_view);
Kotlin:
recyclerView = findViewById(R.id.recycler_view) as RecyclerView
Kotter Knife:
val recyclerView by bindView<RecyclerView>(R.id.recycler_view)
Extensions Library: just import
import kotlinx.android.synthetic.main.my_layout.*

15. Android Extensions Library
Pros:
● Compile time check
● No casts
● Less error prone.
● No libraries in your build.gradle (less methods!) (Butterknife is 342)
● Can import Views from different flavors

16. Anko
Anko is a DSL (Domain-specific language) written in Kotlin to simplify the
programmatically creation of UI.
Much more:
● Intents
● Fragments
● Services
● Configuration qualifiers
● Dialogs and toasts
● Asynchronous tasks
● Logging
● Using SQLite
● Extending Anko

17. val intent = Intent(this, javaClass<SomeActivity>())
intent.putExtra("id", 5)
intent.putExtra("name", "John")
startActivity(intent)
startActivity(Intent(this, SomeActivity::class.java).
putExtra("id", 5).putExtra("name", "John"))
startActivity<SomeActivity>("id" to 5, "name" to "John")
Anko - Intents
Kotlin i.e. 1
Kotlin i.e. 2
Kotlin with Anko

18. async {
// Long background task
uiThread {
result.text = "Done"
}
}
val executor = Executors.newScheduledThreadPool(4)
async(executor) {
// Some task
}
Anko - AsyncTask

19. class SomeActivity : Activity(), AnkoLogger {
private fun someMethod() {
info("London is the capital of Great Britain")
debug(5) // .toString() method will be executed
warn(null) // "null" will be printed
wtf(“Oh, No!”)
}
}
Anko - Logger

20. Kotlin Configuration

21. Configuration
● JDK7
● Android Studio
Preferences -> Plugin - > Install JetBrain Plugins -> Kotlin

22. Configuration
Create a New Project
Tools -> Kotlin -> Configure Kotlin in Project

23. build.gradle (Module :app)
buildscript {
dependencies {
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
}
}
apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
android {
…
…
…
}

24. Kotlin by Examples

25. API: http://thecatapi.com
Endpoint: /api/images/get?format=xml&results_per_page=10
The Amazing Android App for Funny Cats
<response>
<data>
<images>
<image>
<url>
http://24.media.tumblr.com/tumblr_llees8B3V31qbe5pxo1_500.jpg
</url>
<id>9j6</id>
<source_url>http://thecatapi.com/?id=9j6</source_url>
</image>
<image>
<url>
http://25.media.tumblr.com/tumblr_m4g9rvBP441qz6jrko1_400.jpg
</url>
<id>a1k</id>
<source_url>http://thecatapi.com/?id=a1k</source_url>
</image>
</images>
</data>
</response>

26. Ciro Rizzo Enzo Belli
Senior Application Developer @QVC Senior Android Developer @YoYoWallet
@JackRix
http://www.cirorizzo.net/
@enzobelli
© 2016
https://kotlinlang.org/
https://github.com/cirorizzo/KShows
https://github.com/cirorizzo/JShows