This doc for LT. Recommendation using

1. Let’s Try Kotlin!!
Try English LT! for engineers
2023-01-07（Sat）
へー／heisy（SASAKURA Hideyuki）

2. My Profile
● へー／heisy（SASAKURA Hideyuki）
○ Twitter : @heisy
● IT Engineer
● Likes
○ AWS
○ Java
○ Kotlin
○ DDD / TDD
○ Bouldering & Climbing
○ Drinking 🍶🍶🍶

3. Introduction
KotlinFest2022 on 10th Dec 2022.
I was Staff.
But…

4. Introduction
I don’t touch Kotlin for several years
😭

5. Introduction
So I’m Kotlin Lover if not much of one,
I restart Kotlin this year !!
As beginner…😓

6. Agenda
● Why Kotlin?
● How learn Kotlin ?
● More enjoy coding with Kotlin

7. Why Kotlin?
● Concise
● Safe
● Expressive
● Interoperable
● Multiplatform

8. Why Kotlin?: Concise
data class Employee(
val name: String,
val email: String,
val company: String
) // + automatically generated equals(), hashCode(), toString(), and copy()
object MyCompany { // A singleton
const val name: String = "MyCompany"
}
fun main() { // Function at the top level
val employee = Employee("Alice", // No `new` keyword
"alice@mycompany.com", MyCompany.name)
println(employee)
}

9. Why Kotlin?: Safe
fun reply(condition: Boolean): String? = // Nullability is part of Kotlin’s type system
if (condition) "I'm fine" else null
fun error(): Nothing = // Always throw an exception
throw IllegalStateException("Shouldn't be here")
fun main() {
val condition = true // Try replacing `true` with `false` and run the sample!
val message = reply(condition) // The result is nullable
// println(message.uppercase()) // This line doesn't compile
println(message?.replace("fine", "okay")) // Access a nullable value in a safe manner
if (message != null) { // If you check that the type is right,
println(message.uppercase()) // the compiler will smart-cast it for you
}
val nonNull: String = // If the null-case throws an error,
reply(condition = true) ?: error() // Kotlin can infer that the result is non-null
println(nonNull)
}

10. Why Kotlin?: Expressive
val map = mapOf(1 to "one", 2 to "two")
for ((k, v) in map) { // Traverse a map or a list of pairs
println("$k -> $v")
}

11. Why Kotlin?: Expressive
fun obtainKnowledge() = Pair("The Answer", 42) // Single-expression functions
val (description, answer) = obtainKnowledge() // Destructure into a pair of two variables
println("$description: $answer")
getText()?.let { // Apply an action to a nullable expression
sendEmailTo("alice@example.com", it) // if it’s not null
}

12. Why Kotlin?: Expressive
createEmptyWindow()
.apply { // Configure properties of an object
width = 300
height = 200
isVisible = true
}.also { w -> // Perform an additional operation on a call chain
showWindow(w)
}
val fixedIssue = issueById["13456"]
?.takeIf { it.status == Status.FIXED } // Use the value only if the condition is true
println(fixedIssue)

13. Why Kotlin?: Interoperable
Kotlin use JVM library or framework.
Call Kotlin code from Java without an issue.

14. Why Kotlin?: Multiplatform
Kotlin is sharing same code across Android, iOS, Web apps,
JS.

15. How learn Kotlin?
Kotlin learning method is blow.
● Books
● Session/Training movies
● Programing

16. How learn Kotlin?
Kotlin Playground is one of best tools to learn Kotlin.

17. How learn Kotlin?
You will find it easy to get samples from play.kotlinlang.org.

18. How learn Kotlin?
Kotlin has Coroutines. It's exciting!

19. More enjoy coding with Kotlin
We enjoy Kotlin as follows.
● Android apps
● Spring
etc…

20. More enjoy coding with Kotlin
Android mobile development has been Kotlin-first.

21. More enjoy coding with Kotlin
Spring support building web application by Kotlin.

22. More enjoy coding with Kotlin
Visual Studio Code support building Kotlin Web application.

23. So Let’s Try Kotlin !!

24. End

25. Thank you !
Have a nice Kotlin!