OnJava8-Examples/threads/Summing.java

// threads/Summing.java
// (c)2016 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.*;

public class Summing {
  static volatile long x;
  static void timeTest(String id, long checkValue,
    LongSupplier operation) {
    System.out.print(id + ": ");
    long t = System.currentTimeMillis();
    long result = operation.getAsLong();
    long duration = System.currentTimeMillis() - t;
    if(result == checkValue)
      System.out.println(duration + "ms");
    else
      System.out.format("result: %d%ncheckValue: %d%n",
        result, checkValue);
    x = result; // Prevent optimization
  }
  public static final int SZ = 100_000_000;
  // This even works:
  // public static final int SZ = 1_000_000_000;
  // Gauss's formula:
  public static final long CHECK =
    (long)SZ * ((long)SZ + 1)/2;
  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());
    // Takes longer, 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: 631ms
Sum Stream Parallel: 159ms
Sum Iterated: 2560ms
*/