Unable to use coroutines in Kotlin (unresolved reference)

Question

I created gradle java kotlin project. I want to use coroutines but I get unresolved reference launch and unresolved reference delay errors:

import java.util.*
import kotlinx.coroutines.*

fun main (args: Array<String>)
{
    launch { // launch coroutine 
        delay(1000L) 
        println("World!")
    }
    println("Hello")
}

In build.gradle.kts I included this line in dependencies block:

implementation("org.jetbrains.kotlinx", "kotlinx-coroutines-core", "1.5.2")

Answer 1

You have to use runBlocking here, otherwise there won't be a Coroutine Scope where you could call launch and delay .

Working example very similar to yours (taken from your first coroutine ):

fun main(args: Array<String>) = runBlocking { // this: CoroutineScope
    launch { // launch a new coroutine and continue
        delay(1000L) // non-blocking delay for 1 second (default time unit is ms)
        println("World!") // print after delay
    }
    println("Hello") // main coroutine continues while a previous one is delayed
}

Output (as expected):

Hello
World!