OnJava8-Examples/concurrent/ParallelPrime.java at master · CSapprenticeWT/OnJava8-Examples · GitHub

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// concurrent/ParallelPrime.java

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

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

import java.util.*;

import java.util.stream.*;

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

import java.io.*;

import java.nio.file.*;

import onjava.Timer;

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