Why Kotlin is your next language?
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The document outlines the advantages of using Kotlin as a programming language, highlighting its interoperability with Java, static typing, null safety, and concise syntax. It provides examples of Kotlin features such as type inference, immutability, and lambda expressions, as well as its use in Android development and Gradle integration. Additionally, it mentions the growing community and resources available for learning Kotlin.
Why Kotlin is your next language?
- 1. Why Kotlin is your next language? theory and practice Aliaksei Zhynhiarouski 1 Dev Day MiniQ, 2016
- 3. Why is Kotlin • Static Typing bit.ly/st-vs-dyn • Java + Kotlin = ❤. Effortless mixing both in one project • Java Interoperability. 100% interoperable with Java. 3
- 4. Why is Kotlin • Null Safety • Type Inference • Immutability in the mind • fun 4
- 5. fun main(args : Array<String>) { println("Hello, MiniQ!") } 5
- 6. val from_value : Type var from_variable : Type val i_am_string = “mobile” var i_am_long = 666L val i_am_double = 3.14e10 6 val & var
- 7. Null Safety // can’t be null val foo: String = “Dev Day” // need always perform the check val bar: String? = null 7 Type? = Type or null
- 8. Null Safety val bar: String? = “Dev Day” var a = bar?.length // 6 var b = bar?.length?.inc() // 7 var c = bar!!.length // can be NPE 8
- 9. Null Safety val bar: String? = null var a = if (bar != null) bar.length else 0 // 0 var b = bar?.length ?: 0 // 0 9
- 10. Type Definition class Phone(val brand: String) 10 • concise syntax for constructor • properties – not fields • final by default. Use open to open • simple old java class under the hood
- 11. Type Definition class Phone(val brand: String){ var version: Int = 0 } 11 get() {…} private set val phone = Phone(“Apple”) phone.brand == “Apple” // true
- 12. Value Object data class Phone(val brand: String) 12 toString() hashCode() equals() copy()
- 13. Get ready to be inspired 13
- 14. Extensions 14 // Usage Example “MiniQ”.lastChar() // “Q” // Definition fun String.lastChar():Char = this.get(length - 1)
- 15. Extensions 15 // Java under the hood @file:JvmName(“StringUtils") StringUtils.lastChar(“Mobile”);
- 17. Extensions 17 operator fun BigDecimal.inc() = this + BigDecimal.ONE // Example var counter = BigDecimal.ZERO print(++counter) // 1
- 18. Extensions 18 “25”.toInt() // Int “8.$minor.5”.toOsVersion() // to object
- 19. Android Extensions 19 val text = find<TextView>(R.id.text) Just extend Activity and have fun inline fun <reified T : View> Activity.find(id: Int): T = this.findViewById(id) as T final TextView text = (TextView) v.findViewById(R.id.text);
- 20. Lambdas 20 val boys = listOf( Boy(“Alex”), Boy(“Petr”), Boy(“Oleg”)) // 1 boys.filter({ b: Boy -> b.age > 18 }) // 2 boys.filter({ it.age > 18 }) // 3 boys.filter { it.age > 18 }
- 21. λ 21 boys.filter { it.age > 18 } .map { Pair(it, Boy("Eugene")) } .forEach { dance(it) } // Definition inline fun <T> Iterable<T>.filter (predicate: (T) -> Boolean)
- 22. λ 22 db.inTransaction { delete(“users”, “name = ?”, arrayOf(“Alex”)) } fun SQLiteDatabase.inTransaction(func: SQLiteDatabase.() -> Unit) { beginTransaction() try { func() setTransactionSuccessful() } finally { endTransaction() } }
- 23. Delegates – right way 23 class View { } val lazyProp by lazy { “Dev Day” } val ops by observable(“”) { prop, old, new -> print("$old to $new") }
- 24. Delegates – wow way 24 class Activity { } private val btn: Button by lazy { findViewById(R.id.btn) as Button } override fun onCreate(savedBundle: Bundle?) { btn.setText(“MiniQ!”) }
- 25. Delegates – wow way 25 class Query(val props: Map<String, String>) { } val category by props val model by props val info: String get() { return “$category - $model” }
- 26. Delegates – wow way 26 class Query(val props: Map<String, String>) { } val category by props val model by props … val props = mapOf(“category” to “XXX”, “model” to “YYY”) val query = Query(props) print(query.info) // “XXX - YYY”
- 27. DSL 27 • Type-safe • Express your code by flexible syntax • Ideal to build own query engine • if/for/when just inside DSL
- 28. DSL 28 "(#C1 = :active) AND (#C2 = :type) AND " + "(attribute_not_exists(#C1) OR #C1 IN (:model, :allModels)) AND " + "..."; if (smth) append("(#C2 = :active) AND NOT contains(#C3, :brandAll)"); … // wait, oh shi~
- 29. DSL 29 val expr = filterExpr { group { eq("#1", ":2") and eq("#1", ":2") or group { eq("#2", ":2") if (smth) { and eq("#2", ":2") } } and …… }
- 30. One more DSL thing 30 Gradle 3 meets Kotlin
- 31. Kotlin 1.1 typealias Callback<T> = (T) -> T // And now fun alias(cb: Callback<String>) {} 31 Type aliases
- 32. Kotlin 1.1 typealias Table<K> = MutableMap<K, MutableList<String>> 32 Type aliases
- 33. Kotlin 1.1 val future = async<String> { (1..5).map { await(loooongAsyncOperation(it)) }.joinToString("n") } 33 Coroutines with async/await
- 34. Why is Kotlin • Use all existing Java frameworks and libraries • Code reviews are not a problem • Suitable for enterprise Java • Adopting is low risk 34
- 35. Why is Kotlin • Android • Gradle • Can be learned in a few hours • Kotlin also compiles to JavaScript ;) 35
- 37. Links Awesome Kotlin kotlin.link Slack kotlinlang.slack.com Local’s Chat gitter.im/JavaBy/Kotlin 37
- 38. Links just for you Kotlin compilation speed Performance: Kotlin Bytecode https://www.youtube.com/watch?v=eQ4YHpAXdp4 Experience of Square with Kotlin. Good analysis Android Development advanced https://vimeo.com/144877458 Kotlin in real project with a lot of nuances https://www.youtube.com/watch?v=CABN2r4GPpQ 38
- 40. Go v Minsk, ja sozdal