0README.md

$ javac Main.java
$ time java Main
java Main  5.91s user 0.29s system 102% cpu 6.053 total
$ go build -o main
$ time ./main
./main  33.44s user 3.35s system 117% cpu 31.391 total

main.go

package main

import (
	"runtime"
)

func init() {
	runtime.GOMAXPROCS(runtime.NumCPU())
}

func main () {
	for i := 0; i < 10000; i++ {
		m := make(map[int]int)
		for j := 0; j < 10000; j++ {
			if _, exist := m[j]; !exist {
				m[j] = i
			}
		}
	}
}

Main.java

import java.util.Map;
import java.util.HashMap;
 
class Main {
	public static void main(String[] args){
		for (int i = 0; i < 10000; i++) {
			Map<Integer, Integer> m = new HashMap<Integer, Integer>();
			for (int j = 0; j < 10000; j++) {
				if (!m.containsKey(j)) {
					m.put(j, i);
				}
			}
		}
	}
}