// concurrent/ParallelPrime.java

// (c)2021 MindView LLC: see Copyright.txt

// We make no guarantees that this code is fit for any purpose.

// Visit http://OnJava8.com for more book information.

import onjava.Timer;

import java.io.IOException;

import java.nio.file.Files;

import java.nio.file.Paths;

import java.nio.file.StandardOpenOption;

import java.util.List;

import java.util.stream.Collectors;

import static java.util.stream.LongStream.iterate;

import static java.util.stream.LongStream.rangeClosed;

public class ParallelPrime {

static final int COUNT = 100_000;

public static boolean isPrime(long n) {

return rangeClosed(2, (long) Math.sqrt(n))

.noneMatch(i -> n % i == 0);

}

public static void main(String[] args)

throws IOException {

Timer timer = new Timer();

List<String> primes =

iterate(2, i -> i + 1)

.parallel() // [1]

.filter(ParallelPrime::isPrime)

.limit(COUNT)

.mapToObj(Long::toString)

.collect(Collectors.toList());

System.out.println(timer.duration());

Files.write(Paths.get("primes.txt"), primes,

StandardOpenOption.CREATE);

}

}

/* Output:

1635

*/