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// concurrent/Summing.java

// (c)2017 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 java.util.stream.*;

import java.util.function.*;

import onjava.Timer;

public class Summing {

static void timeTest(String id, long checkValue,

LongSupplier operation) {

System.out.print(id + ": ");

Timer timer = new Timer();

long result = operation.getAsLong();

if(result == checkValue)

System.out.println(timer.duration() + "ms");

else

System.out.format("result: %d%ncheckValue: %d%n",

result, checkValue);

}

public static final int SZ = 100_000_000;

// This even works:

// public static final int SZ = 1_000_000_000;

public static final long CHECK =

(long)SZ * ((long)SZ + 1)/2; // Gauss's formula

public static void main(String[] args) {

System.out.println(CHECK);

timeTest("Sum Stream", CHECK, () ->

LongStream.rangeClosed(0, SZ).sum());

timeTest("Sum Stream Parallel", CHECK, () ->

LongStream.rangeClosed(0, SZ).parallel().sum());

timeTest("Sum Iterated", CHECK, () ->

LongStream.iterate(0, i -> i + 1)

.limit(SZ+1).sum());

// Slower & runs out of memory above 1_000_000:

// timeTest("Sum Iterated Parallel", CHECK, () ->

// LongStream.iterate(0, i -> i + 1)

// .parallel()

// .limit(SZ+1).sum());

}

}

/* Output:

5000000050000000

Sum Stream: 167ms

Sum Stream Parallel: 46ms

Sum Iterated: 284ms

*/