concurrent/Summing2.java · ThisYoung/OnJava8-Examples

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OnJava8-Examples

concurrent

Summing2.java

Summing2.java 1.25 KB

// concurrent/Summing2.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.
// {ExcludeFromTravisCI}
import java.util.*;

public class Summing2 {
 static long basicSum(long[] ia) {
 long sum = 0;
 int size = ia.length;
 for(int i = 0; i < size; i++)
 sum += ia[i];
 return sum;
 }
 // Approximate largest value of SZ before
 // running out of memory on my machine:
 public static final 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: 104ms
Parallel: 81ms
Basic Sum: 106ms
parallelPrefix: 265ms
*/

一键复制编辑原始数据按行查看历史

Bruce Eckel 提交于 2017年05月13日 02:53 +08:00 . Try excluding from Travis build

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// concurrent/Summing2.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.
// {ExcludeFromTravisCI}
import java.util.*;

public class Summing2 {
 static long basicSum(long[] ia) {
 long sum = 0;
 int size = ia.length;
 for(int i = 0; i < size; i++)
 sum += ia[i];
 return sum;
 }
 // Approximate largest value of SZ before
 // running out of memory on my machine:
 public static final 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: 104ms
Parallel: 81ms
Basic Sum: 106ms
parallelPrefix: 265ms
*/