44 lines
1.2 KiB
Java
44 lines
1.2 KiB
Java
|
// 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: 114ms
|
||
|
|
Parallel: 27ms
|
||
|
|
Basic Sum: 33ms
|
||
|
|
parallelPrefix: 49ms
|
||
|
|
*/
|