StreamSample.java

package bar.foo;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ThreadLocalRandom;

import static com.google.common.collect.ImmutableList.toImmutableList;
import static java.util.Comparator.*;

public class StreamSample {
  public static void main(String[] args) throws Exception {
    int cnt = 10000000;
    List<Dish> menu = new ArrayList<>();
    for (int i = 0; i < cnt; i++) {
      menu.add(Dish.newRandomDish());
    }

    // parallel stream
    long startTime = System.currentTimeMillis();
    menu.parallelStream()
        .filter(d -> d.getCalorie() < 400)
        .sorted(comparing(Dish::getCalorie))
        .map(Dish::getName)
        .collect(toImmutableList());
    long endTime = System.currentTimeMillis();
    System.out.printf("parallelStream elapsed %dms.\n", (endTime - startTime));

    ForkJoinPool pool = new ForkJoinPool(4);
    startTime = System.currentTimeMillis();
    pool.submit(() -> {
      menu.parallelStream()
          .filter(d -> d.getCalorie() < 400)
          .sorted(comparing(Dish::getCalorie))
          .map(Dish::getName)
          .collect(toImmutableList());
    }).get();
    endTime = System.currentTimeMillis();
    System.out.printf("parallelStream(4) elapsed %dms.\n", (endTime - startTime));

    pool = new ForkJoinPool(8);
    startTime = System.currentTimeMillis();
    pool.submit(() -> {
      menu.parallelStream()
          .filter(d -> d.getCalorie() < 400)
          .sorted(comparing(Dish::getCalorie))
          .map(Dish::getName)
          .collect(toImmutableList());
    }).get();
    endTime = System.currentTimeMillis();
    System.out.printf("parallelStream(8) elapsed %dms.\n", (endTime - startTime));

    // stream
    startTime = System.currentTimeMillis();
    menu.stream()
        .filter(d -> d.getCalorie() < 400)
        .sorted(comparing(Dish::getCalorie))
        .map(Dish::getName)
        .collect(toImmutableList());
    endTime = System.currentTimeMillis();
    System.out.printf("stream elapsed %dms.\n", (endTime - startTime));
  }
}

class Dish {
  private int calorie;
  private String name;

  Dish(int calorie) {
    this.calorie = calorie;
    this.name = String.format("name%d", calorie);
  }

  public int getCalorie() {
    return calorie;
  }

  public String getName() {
    return name;
  }

  public void setCalorie(int calorie) {
    this.calorie = calorie;
  }

  public void setName(String name) {
    this.name = name;
  }

  public static Dish newRandomDish() {
    return new Dish(ThreadLocalRandom.current().nextInt(1, 1000));
  }
}