The document provides an overview of the Kotlin programming language, including what it is, who created it, when it was created, where it can be used, and why it is useful. Specifically: - Kotlin is a programming language created by JetBrains as an alternative to Java that compiles to JVM bytecode. - It was created in 2010 and became open source in 2012, with stable releases beginning in 2016 and support on Android announced by Google in 2017. - Kotlin can run on the JVM for Android and server-side applications as well as JavaScript and native platforms, though cross-platform code cannot use Java libraries. - Advantages include being modern, concise,

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