String::toIntとInteger::parseIntの差はほとんどないっぽい

toInt_parseInt.kt

import kotlin.system.*

fun main(){
    val N = 1_000_000
    val K = 100
    val stringNums = (1..N).map(Int::toString)
    run{
        println("it.toInt()")
        val t = average(K){
            stringNums.map{it.toInt()}
        }
        println(t)
    }
    run{
        println("String::toInt")
        val t = average(K){
            stringNums.map(String::toInt)
        }
        println(t)
    }
    run{
        println("Integer::parseInt")
        val t = average(K){
            stringNums.map(Integer::parseInt)
        }
        println(t)
    }
}

fun average(n: Int, block: () -> Unit) = (1..n).map{
    System.gc()
    System.runFinalization()
    measureTimeMillis{
        block()
    }
}.average()

/***** output *****
it.toInt()
29.11
String::toInt
28.92
Integer::parseInt
29.83
*******************/

時間計測する前にちゃんとgcするのがミソ