Your first coroutine with Kotlin

pljp/kotlinx.coroutines

build.gradle (Modlue.app)

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    ・・・
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.1'
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.2" // step1
 
}

package com.nekotype.ips.api
 
import android.os.AsyncTask
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.*　// step2
 
 
class MainActivity : AppCompatActivity() {
 
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
 
         // click
        button.setOnClickListener {
           println("start: ${Thread.currentThread().name}")
            GlobalScope.launch{
                println("coroutine: ${Thread.currentThread().name}")
            }
            println("end: ${Thread.currentThread().name}")
        }
 
    }
}
 
 ↓
start: main
end: main
coroutine: DefaultDispatcher-worker-1

// thread version
import kotlinx.coroutines.*
import java.util.concurrent.atomic.AtomicLong
import kotlin.concurrent.thread
 
fun main() {
    val c = AtomicLong()
 
    for (i in 1..1_000_000L)
// thread だと数秒まっても終了しないので諦めた
        thread(start = true) {
            c.addAndGet(i)
        }
 
    println(c.get())
 
}
 
　↓
// coroutines version
import kotlinx.coroutines.*
import java.util.concurrent.atomic.AtomicLong
import kotlin.concurrent.thread
 
fun main() {
    runBlocking {
        val sum = deferred.sumBy { it.await() }
        println("Sum: $sum")
    }
}
 
val deferred = (1..1_000_000).map { n ->
    GlobalScope.async {
        n
    }
}
 
// Sum: 1784293664

import kotlinx.coroutines.*
import java.util.concurrent.atomic.AtomicLong
import kotlin.concurrent.thread
 
fun main() {
    runBlocking {
        val sum = deferred.sumBy { it.await() }
        println("Sum: $sum")
    }
}
 
val deferred = (1..1_000_000).map { n ->
    GlobalScope.async {
        delay(1000)
 
        n
    }
}
 ↓
Sum: 1784293664