Kotlin Hands-on

Develop a
weather app
with K

View Slide

Schedule
9:00 - Introduction

9:05 - Intro to Kotlin part 1

9:25 - Project presentation & setup

9:35 - Hands-on part 1 (55 minutes)

10:30 - Coﬀee break



11:55 - Final Part
#androiddev #kotlin #morningtech @ekito

View Slide

Practical notes
https://github.com/Ekito/2017-handson-kotlinAndroid
Grab your stuﬀ !

View Slide

@Baresse
Work @ ekito
Developer & Geek
Fullstack & Mobile
Laurent BARESSE
@arnogiu
Work @ ekito
Core & Gear Maker
Mobile & Cloud
Arnaud GIULIANI

View Slide

https://www.ekito.fr/careers
Join the team !

View Slide

Intro to
part 1

View Slide

« production ready »
15.02.2016

View Slide

Kotlin 1.1.1 @ 15.03.2017

View Slide

Yet another JVM
Language ?

View Slide

The new « Swift »
for Android ?

View Slide


View Slide

What’s
Kotlin ?
- Fully open source (built by Jetbrains)
- Run on Java 6+
- Static typing & type inference
- Modern language features
- 1st grade tooling

View Slide

What’s inside
Kotlin ?
- String templates
- Properties
- Lambdas
- Data class
- Smart cast
- Null safety
- Lazy property
- Default values for function
parameters
- Extension Functions
- No more ;
- Single-expression
functions
- When expression
- let, apply, use, with
- Collections
- Android Extensions Plugin

View Slide

Compare with
Same conciseness and expressive code, but
Kotlin static typing and null-safety make a big
difference.
"Some people say Kotlin has 80% the power of
Scala, with 20% of the features" *  
"Kotlin is a software engineering language in
contrast to Scala which is a computing science
language." *
Swift and Kotlin are VERY similar. Swift is LLVM
based and has C interop while Kotlin is JVM based
and has Java interop.
* Quotes from Kotlin: The Ying and Yang of Programming Languages
@
sdeleuze

View Slide

is Kotlin Android friendly ?
https://github.com/SidneyXu/AndroidDemoIn4Languages
Method counts by Language

View Slide

16
Let’s Go !

View Slide

Typing & Inference
val a: Int = 1 
val b = 1 // `Int` type is inferred
var x = 5 // `Int` type is inferred 
x += 1
Inferred values
Mutable values
val : constant value - IMMUTABLE
var : variable value - MUTABLE
USE VAL AS MUCH AS POSSIBLE !

View Slide

Safety with Optionals
var stringA: String = "foo" 
stringA = null //Compilation error - stringA is a String (non optional) 
 
var stringB: String? = "bar" // stringB is an Optional String 
stringB = null //ok
Optional value

View Slide

Late initialization, Lazy, Delegates …
// set length default value manually 
val length = if (stringB != null) stringB.length else -1 
//or with the Elvis operator 
val length = stringB?.length ?: -1
Default Value & Elvis Operator
val length = stringB.length // Compilation error - stringB can be null ! 
// use ? the safe call operator 
val length = stringB?.length //Value or null - length is type Int?
val length = stringB!!.length // Value or explicit throw NPE - length is type Int
Safe call with ?. or Explicit call with !!.

View Slide

Example
Working with optional values

View Slide

Example
Null check safety & Smart cast
Securing with default values

View Slide

Class
class User ( 
val userName: String, 
val ﬁrstName: String, 
val lastName: String, 
var location: Point? = null 
)
POJO +
- Getter
- Setter
- Constructors
public / closed by default

View Slide

Data Class
data class User ( 
val userName: String, 
val ﬁrstName: String, 
val lastName: String, 
var location: Point? = null 
)
POJO +
- Getter
- Setter
- Constructors
- toString
- hashcode
- equals
- copy

View Slide

POJO ?
Kotlin
Java

View Slide

Properties
// readonly property 
val isEmpty: Boolean 
get() = this.size == 0
Properties can be declared in constructor or in class
You can also handle getter & setter
// customer getter & setter 
var stringRepresentation: String
set(value) { 
…
}
class ApiKey(var weatherKey: String, var geocodeKey: String){ 
var debug : Boolean = false 
}

View Slide

Object Component
// singleton 
object Resource { 
val name = "Name" 
}
class StringCalculator{
// class helper 
companion object{ 
val operators = arrayOf("+","-","x","/") 
} 
}
Singleton Class
Companion Object

View Slide

Example
data class User(val name: String = "", val age: Int = 0)
val jack = User(name = "Jack", age = 1) //no new keyword 
val anotherJack = jack.copy(age = 2)
Data Class usage
A simple GSon Class

View Slide

When
when (s) { 
1 -> print("x == 1") 
2 -> print("x == 2") 
else -> { // Note the block 
print("x is neither 1 nor 2") 
} 
}
Flow Control (replace your old if blocks)
in ->
is ->
expression ->
when (x) { 
in 1..10 -> print("x is in the range") 
in validNumbers -> print("x is valid") 
!in 10..20 -> print("x is outside the range") 
else -> print("none of the above") 
}
Pattern Matching
* can match with operators : in, as, is, range …

View Slide

Example

View Slide

Collections
// immutable map 
val map = mapOf("a" to 1, "b" to 2, "c" to 3) 
for ((k, v) in map) { 
println("$k -> $v") 
}
 
map2["a"] = "my value" // direct map access with array style
// range 
for (i in 1..100) { //... }
// immutable list 
val list = listOf("a", "b", "c","aa") 
list.ﬁlter { it.startsWith("a") }
* collections operators : map, filter, take, flatMap, forEach, firstOrNull, last …

View Slide

Example
Kotlin Collection
Java 7 Collection

View Slide

InterOp
object UserSingleton{ 
fun stringify(user : User) : String{ 
val (name,age) = user 
return "[name=$name][age=$age]" 
} 
} 
 
fun WhatIsyourAge(user : User){ 
println("Your age is ${user.age}") 
} 
 
data class User (val name: String, val age : Int){ 
companion object{ 
fun sayHello(user : User){ 
println("Hello ${user.name}") 
} 
} 
}
User u = new User("toto",42); 
User.Companion.sayHello(u); 
UserUtilsKt.WhatIsyourAge(u); 
System.out.println("stringify : "+UserSingleton.INSTANCE.stringify(u));
Kotlin code
Calling Kotlin from Java

View Slide

Project presentation
& setup

View Slide

My Weather app

View Slide

Get the project
https://github.com/Ekito/2017-handson-kotlinAndroid

View Slide

Create your branch
https://github.com/Ekito/2017-handson-kotlinAndroid/blob/master/README.pdf

View Slide

MainApplication MainActivity
DailyForecastModel
DialogHelper
WeatherSDKUtil
WeatherSDK

View Slide

Hands-on
part 1

View Slide

9:00 - Introduction






11:55 - Final Part
Hands-on !

View Slide

9:00 - Introduction






11:55 - Final Part
Coffee Break !

View Slide

Intro to
part 2

View Slide

Sweet stuffs for

View Slide

Kotlin’s Android
Extensions
apply plugin: 'com.android.application'
apply plugin: ‘kotlin-android’
apply plugin: ‘kotlin-android-extensions’ // if use extensions

View Slide

Kotlin
Java
* In Fragment : onViewCreated()

View Slide

Functions
fun reformat(str: String, 
normalizeCase: Boolean = true, 
upperCaseFirstLetter: Boolean = true, 
wordSeparator: Char = ' '): String { 
 
}
Named Parameters & default values
reformat(str, true, true, '_') // old way to call 
reformat(str, wordSeparator = '_') // using default values & named params
fun String.hello(): String = "Hello " + this
val hi = "Arnaud !".hello() 
println("$hi") // Hello Arnaud !
Extension

View Slide

Lambdas
val fab = findViewById(R.id.fab) as FloatingActionButton 
fab.setOnClickListener { view -> popLocationDialog(view) }
A lambda expression or an anonymous function is a “function literal”, i.e. a function that is
not declared, but passed immediately as an expression
- A lambda expression is always surrounded by curly braces
- Its parameters (if any) are declared before -> (parameter types may be omitted),
- The body goes after -> (when present).
myNumber.split("\n").flatMap { it.split(separator) } 
.map(Integer::parseInt) 
.map(::checkPositiveNumber) 
.filter { it <= 1000 } 
.sum()
* Method references are not surrounded by curly braces

View Slide

Reactive
Programming

View Slide

Lamba expressions
Functional Programming
Reactive Streams
http://reactivex.io/documentation/operators.html
http://www.reactive-streams.org/
https://spring.io/blog/2016/06/07/notes-on-reactive-
programming-part-i-the-reactive-landscape

View Slide

Kotlin Hands-on

Kotlin Hands-on

Laurent BARESSE

More Decks by Laurent BARESSE

Other Decks in Technology

Featured

Transcript