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plugins {
    kotlin("kapt") version "1.9.23"
}

plugins {
    id "org.jetbrains.kotlin.kapt" version "1.9.23"
}

plugins {
    kotlin("plugin.noarg") version "1.9.23"
}

plugins {
    id "org.jetbrains.kotlin.plugin.noarg" version "1.9.23"
}

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Some text here and a codeblock:

plugins {
    kotlin("plugin.noarg") version "1.9.23"
}

Codeblocks

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    import java.util.*

@Service
class MessageService(val db: MessageRepository) {
    fun findMessages(): List<Message> = db.findAll().toList()

    fun findMessageById(id: String): List<Message> = db.findById(id).toList()

    fun save(message: Message) {
        db.save(message)
    }

    fun <T : Any> Optional<out T>.toList(): List<T> =
        if (isPresent) listOf(get()) else emptyList()
}

Expandable codeblock

package com.example.demo import org.springframework.boot.autoconfigure.SpringBootApplication import org.springframework.boot.runApplication import org.springframework.web.bind.annotation.GetMapping import org.springframework.web.bind.annotation.RequestParam import org.springframework.web.bind.annotation.RestController @SpringBootApplication class DemoApplication fun main(args: Array<String>) { runApplication<DemoApplication>(*args) } @RestController class MessageController { @GetMapping("/") fun index(@RequestParam("name") name: String) = "Hello, $name!" }

Runnable codeblock

data class User(val name: String, val id: Int)

fun main() {
    val user = User("Alex", 1)
    
    //sampleStart
    // Automatically uses toString() function so that output is easy to read
    println(user)            
    // User(name=Alex, id=1)
    //sampleEnd
}

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Primitive-type array	Equivalent in Java
`BooleanArray`	`boolean[]`
`ByteArray`	`byte[]`
`CharArray`	`char[]`
`DoubleArray`	`double[]`
`FloatArray`	`float[]`
`IntArray`	`int[]`
`LongArray`	`long[]`
`ShortArray`	`short[]`

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Last modified on	December 2023
Next update	June 2024

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Before	Now
kotlin { targets { configure(['windows', 'linux']) { } } }	kotlin { targets { configure([findByName('windows'), findByName('linux')]) { } } }

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	Before	Now
Dependencies of the `jvmMain` compilation	jvm<Scope>	jvmCompilation<Scope>
Dependencies of the `jvmMain` compilation	dependencies { add("jvmImplementation", "foo.bar.baz:1.2.3") }	dependencies { add("jvmCompilationImplementation", "foo.bar.baz:1.2.3") }
Dependencies of the `jvmMain` source set	jvmMain<Scope>
Dependencies of the `jvmTest` compilation	jvmTest<Scope>	jvmTestCompilation<Scope>
Dependencies of the `jvmTest` source set	jvmTest<Scope>

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1. Three point 1
2. Three point 2
3. Three point 3
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jvmTest<Scope>

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First bullet
Second bullet
Third bullet
- One more
- Another one
  - Wow, one more
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jvmTest<Scope>

Definition list

Collapsible item #1

The return type of the findById() function in the CrudRepository interface is an instance of the Optional class. However, it would be convenient to return a List with a single message for consistency. For that, you need to unwrap the Optional value if it’s present, and return a list with the value. This can be implemented as an extension function to the Optional type.

In the code, Optional<out T>.toList(), .toList() is the extension function for Optional. Extension functions allow you to write additional functions to any classes, which is especially useful when you want to extend functionality of some library class.

Collapsible item #2

This function works with an assumption that the new object doesn’t have an id in the database. Hence, the id should be null for insertion.

If the id isn’t null, CrudRepository assumes that the object already exists in the database and this is an update operation as opposed to an insert operation. After the insert operation, the id will be generated by the data store and assigned back to the Message instance. This is why the id property should be declared using the var keyword.

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variable using: latest Kotlin version is 2.0.21

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