Niektóre rzeczy trzeba dobrze przyprawić żeby były lepsze ... tak samo jest z pisaniem aplikacji na Androida. Jako programiści zaczynamy mieć czasami dość Javy i chcielibyśmy się przerzucić na coś lepszego i czytelniejszego. Takim rozwiązaniem może okazać się Kotlin. O zaletach języka i o tym jak może ułatwić pracę z Androidem dowiecie się podczas tego wykładu.

2. otlin - Let's ketchup it
Author: Michał Szczepanik

3. About me

4. Dream on

5. Frist Law of Software Quality
E=mc2
Error=(more code)2

8. otlin
• created by JetBrains
• open sourced :)
• statically typed programming language
• runs on JVM
• can be compiled to JavaScript source code
• works on Spring Boot

9. Modern & Pragmatic
concise
expressive
safe & fast
can be easily mixed with

10. Let’s have fun with Hello
fun main(args : Array<String>) {
val scope = "world"
println("Hello, $scope!")
}

11. How to start ?

12. Lang syntax
fun sum(a: Int, b: Int): Int {
return a + b
}
fun sum(a: Int, b: Int) = a + b

13. Diffs
classes, funs are final by default
primitive type
== works like java’s .equals()

14. Lambdas
val sum: (Int, Int) -> Int = {x: Int, y: Int -> x+y}
val sum = {x: Int, y: Int -> x + y}
fun apply(i: Int, f: (Int) -> Int) = f(i)
apply(9, {x -> x + 60})
apply(9) {x -> x + 60}

15. Lambdas
firstName.validateWith { !it.notEmpty }
lastName.validateWith { !it.notEmpty }
val notEmpty: (String) -> Boolean = { !it.notEmpty }
firstName.validateWith(notEmpty)
lastName.validateWith(notEmpty)

16. Null
Pointer

17. Null Safety
(Nullable types and Non-Null Types)
var a: String = "abc"
a = null // compilation error
var b: String? = "abc"
b = null // ok

18. Null Safety
if(b != null){
return b.lenght()
}
b?.lenght()
b!! //NPE
val l = b?.length() ?: 0

20. Extension Functions
fun Activity.toast( msg: CharSequence,
dtn: Int = Toast.LENGTH_SHORT){
Toast.makeText(this, msg, dtn)
}
toast("Short Toast!!")
toast("Long Toast!!", Toast.LENGTH_LONG)

21. Default & Named Arguments
fun reformat( str: String,
normalizeCase: Boolean = true,
upperCaseFirstLetter: Boolean = true,
divideByCamelHumps: Boolean = false,
wordSeparator: Char = ' ') {
...
}
reformat(str)
reformat(str, upperCaseFirstLetter = false )

22. Singleton
public object TheSingleton {
public fun drink() {
...
}
}
TheSingleton.drink()

23. Extension Function Expresions
db.beginTransaction();
try {
db.delete("user", "name = ?", new String[] {"Michael"});
db.setTransactionSuccessful();
} finally {
db.endTransaction();
}

24. Extension Function Expresions
fun SQLiteDatabase.inTransaction(func: () -> Unit){
beginTransaction()
try {
func()
setTransactionSuccessful()
} finally {
endTransaction()
}
}
db.inTransaction {
db.delete("user", "name = ?", new String[] {"Michael"})
}

25. Extension Function Expresions
inline fun SQLiteDatabase.inTransaction(
func: SQLiteDatabase.() -> Unit){
beginTransaction()
try {
func()
setTransactionSuccessful()
} finally {
endTransaction()
}
}
db.inTransaction {
delete("user", "name = ?", new String[] {"Michael"})
}

26. Kotlin Android Extensions
(Goodbye findViewById)
<Button
android:id="@+id/click_me_button"
/>
class KotlinActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?)
{
...
click_me_button.setOnClickListener {....}
...
}
}

27. Kotlin Android Extensions
(startActivity)
val intent = Intent(this, javaClass<NewActivity>())
intent.putExtra("VALUE", 1)
intent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP)
startActivity(intent)
startActivity(intentFor<NewActivity>("VALUE" to 1).singleTop())
startActivity<NewActivity>("VALUE" to 1)

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

29. Write executable specifications
@Test
public void testCalculateTaxRate() {
TaxRateCalc calculator = new TaxRateCalc();
Integer value = calculator.calculateRate(200, 10);
assertEquals(300,value);
}

30. Write executable specifications
class TaxCalculatorSpecs: Spek() { init {
given("Tax rate calculator with default locale settings") {
val taxRateCalc = TaxRateCalc ()
on("calculating the rate for an income of 200 and an average
change of 10 per semester") {
val value = taxRateCalculator.calculateRate(200, 10)
it("should result in a value of 300") {
assertEquals(300, value)
}
}
}
}}

31. Library Jar Size Dex Size Method Count Field Count
kotlin-runtime-0.10.195 354 KB 282 KB 1071 391
kotlin-stdlib-0.10.195 541 KB 835 KB 5508 458
Library Jar Size Dex Size Method Count Field Count
scala-library-2.11.5 5.3 MB 4.9 MB 50801 5820
groovy-2.4.0-grooid 4.5 MB 4.5 MB 29636 8069
guava-18.0 2.2 MB 1.8 MB 14833 3343
Source: Using Project Kotlin for Android by Jake Wharton

32. Library Jar Size Dex Size Method Count Field Count
rxjava-1.0.4 678 KB 513 KB 3557 1668
support-v4-21.0.3 745 KB 688 KB 6721 1886
play-services-base-6.5.87 773 KB 994 KB 5212 2252
okio-1.2.0 54 KB 55 KB 508 76
okhttp-2.2.0 304 KB 279 KB 1957 882
retrofit-1.9.0 119 KB 93 KB 766 228
picasso-2.4.0 112 KB 97 KB 805 342
dagger-1.2.2 59 KB 54 KB 400 119
butterknife-6.0.0 48 KB 50 KB 307 73
wire-runtime-1.6.1 71 KB 71 KB 471 147
gson-2.3.1 206 KB 170 KB 1231 390
Total 2963 KB 2894 KB 21935 8063

34. and

35. I want much more
https://kotlinlang.org/ (kotl.in)
https://github.com/Kotlin/anko

36. Thank you for your attention
michal.szczepanik@blstream.com
meet.mobile.@blstream.com

37. michal.szczepanik@blstream.com
meet.mobile@blstream.com