Comparing performance of sequential and parallel stream operations. - Java Lambda Stream

Java examples for Lambda Stream:Parallel Stream

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Description

Comparing performance of sequential and parallel stream operations.

Demo Code

import java.time.Duration;
import java.time.Instant;
import java.util.Arrays;
import java.util.LongSummaryStatistics;
import java.util.stream.LongStream;
import java.security.SecureRandom;

public class Main
{
   public static void main(String[] args)
   {/*  w  w w  . j  av a2s  .  co m*/
      SecureRandom random = new SecureRandom();

      // create array of random long values
      long[] values = random.longs(10_000_000, 1, 1001).toArray();
 
      // perform calculcations separately
      Instant separateStart = Instant.now(); 
      long count = Arrays.stream(values).count();
      long sum = Arrays.stream(values).sum();
      long min = Arrays.stream(values).min().getAsLong();
      long max = Arrays.stream(values).max().getAsLong();
      double average = Arrays.stream(values).average().getAsDouble();
      Instant separateEnd = Instant.now(); 

      // display results
      System.out.println("Calculations performed separately");
      System.out.printf("    count: %,d%n", count);
      System.out.printf("      sum: %,d%n", sum);
      System.out.printf("      min: %,d%n", min);
      System.out.printf("      max: %,d%n", max);
      System.out.printf("  average: %f%n", average);
      System.out.printf("Total time in milliseconds: %d%n%n", 
         Duration.between(separateStart, separateEnd).toMillis());

      // time sum operation with sequential stream
      LongStream stream1 = Arrays.stream(values);
      System.out.println("Calculating statistics on sequential stream");
      Instant sequentialStart = Instant.now(); 
      LongSummaryStatistics results1 = stream1.summaryStatistics();
      Instant sequentialEnd = Instant.now();

      // display results
      displayStatistics(results1);
      System.out.printf("Total time in milliseconds: %d%n%n", 
         Duration.between(sequentialStart, sequentialEnd).toMillis());

      // time sum operation with parallel stream
      LongStream stream2 = Arrays.stream(values).parallel();
      System.out.println("Calculating statistics on parallel stream");
      Instant parallelStart = Instant.now(); 
      LongSummaryStatistics results2 = stream2.summaryStatistics();
      Instant parallelEnd = Instant.now();

      displayStatistics(results1);
      System.out.printf("Total time in milliseconds: %d%n%n", 
         Duration.between(parallelStart, parallelEnd).toMillis());
   }

   private static void displayStatistics(LongSummaryStatistics stats)
   {
      System.out.println("Statistics");
      System.out.printf("    count: %,d%n", stats.getCount());
      System.out.printf("      sum: %,d%n", stats.getSum());
      System.out.printf("      min: %,d%n", stats.getMin());
      System.out.printf("      max: %,d%n", stats.getMax());
      System.out.printf("  average: %f%n", stats.getAverage());
   }
}

Result


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