// threads/Summing2.java

// (c)2016 MindView LLC: see Copyright.txt

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

// Visit http://mindviewinc.com/Books/OnJava/ for more book information.

import java.util.*;

public class Summing2 {

static long basicSum(long[] ia) {

long sum = 0;

final int sz = ia.length;

for(int i = 0; i < sz; i++)

sum += ia[i];

return sum;

}

// Approximate largest value of SZ before

// running out of memory on my machine:

public static int SZ = 20_000_000;

public static final long CHECK =

(long)SZ * ((long)SZ + 1)/2;

public static void main(String[] args) {

System.out.println(CHECK);

long[] la = new long[SZ+1];

Arrays.parallelSetAll(la, i -> i);

Summing.timeTest("Array Stream Sum", CHECK, () ->

Arrays.stream(la).sum());

Summing.timeTest("Parallel", CHECK, () ->

Arrays.stream(la).parallel().sum());

Summing.timeTest("Basic Sum", CHECK, () ->

basicSum(la));

// Destructive summation:

Summing.timeTest("parallelPrefix", CHECK, () -> {

Arrays.parallelPrefix(la, Long::sum);

return la[la.length - 1];

});

}

}

/* Output:

200000010000000

Array Stream Sum: 112ms

Parallel: 28ms

Basic Sum: 33ms

parallelPrefix: 60ms

*/