Kotlin from scratch

Do you want to learn #Kotlin programming language from scratch? This is the first episode of my simple course.

Transcript

1. Kotlin from scratch franco.lombardo@smeup.com - https://www.linkedin.com/in/francolombardo/
2. Kotlin The five Wh questions • What? • Who? • When? • Where? • Why?
3. What is Kotlin? Kotlin is a programming language with a syntax similar to C / Java / JavaScript / C# • Strong typing (a number is not a string) • Static typing (types of variables are checked at compile time) • Type inference (type declaration can often be omitted) • Object Oriented Programming (classes, objects, methods, inheritance, polymorphic calls) • Functional Programming Paradigm (functions are types, so we can pass them around)
4. Who created Kotlin? • Kotlin was created by JetBrains, a company that builds programming languages IDEs and tools such as IntelliJ IDEA • There is a Kotlin Foundation created with Google to protect the trademarks and to design the development path • Open source licensed under Apache 2 • Kotlin is the name of an island near St. Petersburg (Java is the name of an island, too)
5. When was Kotlin created? • 2010: Start of the Kotlin project • 2012: The project becomes Open Source • 2016: First stable release • 2017: Google announces support on Android • 2019: It becomes the preferred language for Android
6. Where does Kotlin run? • JVM: primary target, the only one that is battle-proven • JS: browser and server (NodeJS) (early stage) • Native: iOS and more (early stage) Be careful: cross platform code cannot use Java libraries!
7. Why Kotlin? • It’s modern (OOP + functional + coroutines +…) • It’s concise • It’s interoperable • it can reuse Java libraries ecosystem • it can be used by Java projects • It’s multiplatform (maybe?) • It handles null values in a safer way • Decoupling the evolution of the language from the evolution of the JVM (e.g. phones, AS400, mission critical production servers)
8. Why Kotlin? Working in Kotlin is a lot of fun! J
9. The very recommended IDE for Kotlin
10. The very recommended IDE for Kotlin
11. The very recommended IDE for Kotlin
12. The very recommended building system for Kotlin Sample project: https://github.com/f-lombardo/kotlin-from-scratch
13. Strong static typing with inference fun main() { val authorOfNabucco: String = "Giuseppe Verdi" val authorOfTurandot = "Giacomo Puccini" println("Italian composers: $authorOfNabucco and $authorOfTurandot") }
14. Strong static typing with inference fun main() { val authorOfNabucco: String = "Giuseppe Verdi" val authorOfTurandot = "Giacomo Puccini" println("Italian composers: $authorOfNabucco and $authorOfTurandot") } Explicit type declaration Type inference String interpolation Immutable variables are preferred
15. Multiline strings: Kotlin is concise Test blocks of RPG CODE easily
16. Kotlin is concise: why is it important? Concise ↓ Less boilerplate code ↓ Easier to understand (less cognitive overload) ↓ Fewer bugs
17. How much is Kotlin concise? Data class: Java Bean with hashCode, toString, equals and much more
18. How much is Kotlin concise? Decompiled Java version of the previous data class (just a part of it)
19. Default arguments Default arguments = less overloading!!!
20. Kotlin is safer Can be null Cannot be null val italianComposer: String = "Giuseppe Verdi" val dutchComposer: String? = null
21. val result = openDatabase("franco", "secret") ?.findFirstComposerByNation("Italy") ?.findOperaByYear(1871) ?: "No results" Kotlin is safer Composing nullable values/functions in a safe way Possibly null Not null
22. val result = openDatabase("franco", "secret") ?.findFirstComposerByNation("Italy") ?.findOperaByYear(1871) ?: "No results" Kotlin is safer Composing nullable values/functions in an expressive way “or else” “and then”
23. Extension functions data class Database(val composers: List<Composer>) data class Composer(val name: String, val nation: String, val operas: List<Opera>) data class Opera(val name: String, val yearOfComposition: Int) fun Database.findFirstComposerByNation(nation: String): Composer? = this.composers.firstOrNull { it.nation == nation } fun Composer.findOperaByYear(year: Int): Opera? = this.operas.firstOrNull { it.yearOfComposition == year } Extending classes from outside
24. Extension functions Code organization based on domain aspects Extension methods for domain objects regarding the “SQL aspect”
25. The power of lambdas val elapsedTime = measureTimeMillis { execute(compilationUnit.main.stmts) } public fun measureTimeMillis(block: () -> Unit): Long { val start = System.currentTimeMillis() block() return System.currentTimeMillis() - start }
26. References Kotlin in action Dmitry Jemerov, Svetlana Isakova Kotlin for Java Developers https://www.coursera.org/learn/kotlin-for-java-developers JetBrains Kotlin Academy https://hyperskill.org/onboarding/?track=kotlin JetBrains Kotlin playlist on YouTube https://bit.ly/kotlinTube Kotlin hands-on labs (Coroutines, JS, Native) https://play.kotlinlang.org/hands-on/overview