Introduction to Kotlin Language and its application to Android platform
6 likes1,202 views
Kotlin is a modern programming language developed by JetBrains that runs on the Java Virtual Machine (JVM) and offers seamless interoperability with Java. It features concise syntax, null safety, type inference, and supports functional programming styles, making Android development easier and more expressive. The language comes with useful libraries, resolves many issues found in Java, and is increasingly adopted despite some compile-time overhead and resource demands.
![Lambdas
strings
.filter( { it.count { it in "aeiou" } >= 3 } )
.filterNot { it.contains("ab|cd|pq|xy".toRegex()) }
.filter { s -> s.contains("([a-z])1".toRegex()) }
.size.toString()](https://image.slidesharecdn.com/introductiontokotlinlanguageitsapplicationtoandroidplatform-160726173349/85/Introduction-to-Kotlin-Language-and-its-application-to-Android-platform-24-320.jpg)
![Lambdas
strings
.filter( { it.count { it in "aeiou" } >= 3 } )
.filterNot { it.contains("ab|cd|pq|xy".toRegex()) }
.filter { s -> s.contains("([a-z])1".toRegex()) }
.size.toString()](https://image.slidesharecdn.com/introductiontokotlinlanguageitsapplicationtoandroidplatform-160726173349/85/Introduction-to-Kotlin-Language-and-its-application-to-Android-platform-28-320.jpg)
Introduction to Kotlin Language and its application to Android platform
- 1. Introduction to Kotlin language & its application to Android platform
- 2. Overview
- 3. What is Kotlin • Kotlin is a new programming language by Jetbrains. • It runs on JVM stack. • It has ≈zero-cost Java interop. • It runs on Android, easily.
- 4. Let’s go! • Kotlin is a new programming language by Jetbrains. • It runs on JVM stack. • It has ≈zero-cost Java interop. • It runs on Android, easily.
- 5. Hello, world! fun main(args: Array<String>) { println("Hello, world!") }
- 6. Hello, world! fun main(args: Array<String>) = println("Hello, world!")
- 7. Hello, world! fun main(args: Array<String>) = args.joinToString(postfix = "!") .forEach { print(it) } > kotlin HelloKt Hello world
- 8. Why Kotlin? • Concise — write less boilerplate. • Interoperable — write alongside your Java code. • Multi-paradigm — you can write functional-alike code. • Promising — developed by developers for developers. • It runs on Android, easily!
- 10. Why Kotlin? • Android runs using fork of Apache Harmony (≈Java 6). • Starting from Android API 19 (Android 4.4) it supports Java 7 features. • Android N (Nutella? 6.1?) brings support for Java 8. • But it is still Java…
- 11. Why Kotlin? • There are lot of modern features and approaches that are unavailable even in Java 8. • Typical Java code is bloated, has a lot of boilerplate. • Kotlin is much more expressive than Java.
- 12. Why Kotlin? final Config config = playlist.getConfig(); if (config != null && config.getUrls() != null) { for (final Url url : config.getUrls()) { if (url.getFormat().equals("txt")) { this.url = url; } } }
- 13. Why Kotlin? playlist.config?.urls ?.firstOrNull { it.format == "txt" } ?.let { this.url = it.url }
- 14. Kotlin features
- 15. Null safety • You won’t see NPE anymore (unless you want) • In pure Kotlin, you can have something non-null: • var foo: String = "foo" • Or nullable • var bar: String? = "bar" • Then: • foo = null → compilation error • bar = null → OK
- 16. Null safety • var foo: String = "foo" • var bar: String? = "bar" • foo.length → 3 • bar.length → ???
- 17. Null safety • var foo: String = "foo" • var bar: String? = "bar" • foo.length → 3 • bar.length → compilation error • Call is null-unsafe, there are two methods to fix it: • bar?.length → 3 (or null if bar == null) • bar!!.length → 3 (or NPE if bar == null)
- 18. Null safety • var foo: String = "foo" • var bar: String? = "bar" • if (bar != null) { • // bar is effectively not null, it can be treated as String, not String? • bar.length → 3 • }
- 19. Null safety • Kotlin understands lot of Java annotations for null-safety (JSR-308, Guava, Android, Jetbrains, etc.) • If nothing is specified, you can treat Java object as Nullable
- 20. Null safety • Kotlin understands lot of Java annotations for null-safety (JSR-308, Guava, Android, Jetbrains, etc.) • If nothing is specified, you can treat Java object as Nullable • Or NotNull! • It’s up to you, and you should take care of proper handling nulls.
- 21. Type inference • var bar: CharSequence? = "bar" • if (bar != null && bar is String) { • // bar can be treated as String without implicit conversion • bar.length → 3 • }
- 22. Type inference • fun List.reversed() = Collections.reverse(list) • Return type List is inferred automatically • //effectively fun List.reversed() : List = Collections.reverse(list)
- 23. Lambdas • Kotlin has it • And it helps a lot • Works fine for SAM
- 24. Lambdas strings .filter( { it.count { it in "aeiou" } >= 3 } ) .filterNot { it.contains("ab|cd|pq|xy".toRegex()) } .filter { s -> s.contains("([a-z])1".toRegex()) } .size.toString()
- 25. Lambdas • Can be in-lined. • Can use anonymous class if run on JVM 6. • Can use native Java lambdas if run on JVM 8.
- 26. Expressivity • new Foo() → foo() • foo.bar(); → foo.bar() • Arrays.asList("foo", "bar") → listOf("foo", "bar")
- 27. Collections operations • Lot of functional-alike operations and possibilities. • You don’t need to write loops anymore. • Loops are not prohibited. • We can have Streams on Java 6.
- 28. Lambdas strings .filter( { it.count { it in "aeiou" } >= 3 } ) .filterNot { it.contains("ab|cd|pq|xy".toRegex()) } .filter { s -> s.contains("([a-z])1".toRegex()) } .size.toString()
- 29. Java Beans, POJOs and so on • Write fields • Write constructors • Write getters and setters • Write equals() and hashCode() • …
- 30. Properties • var age: Int = 0 • Can be accessed as a field from Kotlin. • Getters and setters are generated automatically for Java. • If Java code has getters and setters, it can be accessed as property from Kotlin • Can be computed and even lazy
- 31. Data classes • data class User(var name: String, var age: Int) • Compiler generates getters and setters for Java interop • Compiler generates equals() and hashCode() • Compiler generates copy() method — flexible clone() replacement
- 32. Data classes • data class User(val name: String, val age: Int) • 5 times less LOC. • No need to maintain methods consistency. • No need to write builders and/or numerous constructors. • Less tests to be written.
- 33. Data classes • Model and ViewModel conversion to Kotlin • Made automatically • Was: 1750 LOC in 23 files • Now: 800 LOC • And lot of tests are now redundant!
- 34. Extension methods • Usual Java project has 5-10 *Utils classes. • Reasons: • Some core/library classes are final • Sometimes you don’t need inheritance • Even standard routines are often wrapped with utility classes • Collections.sort(list)
- 35. Extension methods • You can define extension method • fun List.sort() • Effectively it’ll have the same access policies as your static methods in *Utils • But it can be called directly on instance! • fun List.sort() = Collections.sort(this) • someList.sort()
- 36. Extension methods • You can handle even null instances: fun String?.toast(context: Context) { if (this != null) Toast.makeToast(context, this, Toast.LENGTH_LONG).show() }
- 37. String interpolation • println("Hello, world!") • println("Hello, $name!") • println("Hello, ${name.toCamelCase()}!")
- 38. Anko • DSL for Android verticalLayout { val name = editText() button("Say Hello") { onClick { toast("Hello, ${name.text}!") } } }
- 39. Anko • DSL for Android. • Shortcuts for widely used features (logging, intents, etc.). • SQLite bindings. • Easy (compared to core Android) async operations.
- 40. Useful libraries • RxKotlin — FRP in Kotlin manner • Spek — Unit tests (if we still need it) • Kotlin Android extensions — built-it ButterKnife • Kotson — Gson with Kotlin flavor
- 41. Summary
- 42. Cost of usage Each respective use has a .class method cost of • Java 6 anonymous class: 2 • Java 8 lambda: 1 • Java 8 lambda with Retrolambda: 6 • Java 8 method reference: 0 • Java 8 method reference with Retrolambda: 5 • Kotlin with Java Runnable expression: 3 • Kotlin with native function expression: 4
- 43. Cost of usage • Kotlin stdlib contains ≈7K methods • Some part of stdlib is going to be extracted and inlined compile-time • And ProGuard strips unused methods just perfect
- 44. Build and tools • Ant tasks, Maven and Gradle plugins • Console compiler and REPL • IntelliJ IDEA — out of the box • Android Studio, other Jetbrains IDEs — as plugin • Eclipse — plugin
- 45. Build and tools • Can be compiled to run on JVM. • Can be run using Jack (Java Android Compiler Kit) • Can be compiled to JS. • Can be used everywhere where Java is used.
- 46. Kotlin pros and cons • It’s short and easy. • It has zero-cost Java interoperability. • You’re not obliged to rewrite all your code in Kotlin. • You can apply modern approaches (like FRP) without bloating your code. • And you could always go back to Java (but you won’t). • Longer compile time. • Heavy resources usage. • Some overhead caused by stdlib included in dex file. • Sometimes errors are cryptic. • There are some bugs and issues in language and tools. • Community is not so huge as Java one.
- 47. Useful Resources
- 48. Books • Kotlin for Android Developers. • The first (and only) book about Kotlin • Regular updates with new language features • https://leanpub.com/kotlin-for-android- developers
- 49. Books • Kotlin in Action. • A book by language authors • WIP, 8/14 chapters are ready, available for early access • https://www.manning.com/books/kotlin- in-action
- 50. Links • https://kotlinlang.org — official site • http://blog.jetbrains.com/kotlin/ — Jetbrains blog • http://kotlinlang.slack.com/ + http://kotlinslackin.herokuapp.com/ — community Slack channel • https://www.reddit.com/r/Kotlin/ — subreddit • https://github.com/JetBrains/kotlin — it’s open, yeah! • https://kotlinlang.org/docs/tutorials/koans.html — simple tasks to get familiar with language. • http://try.kotlinlang.org — TRY IT, NOW!
- 51. THANK YOU Oleg Godovykh Software Engineer [email protected] 202-295-3000 http://eastbanctech.com