Stream.concat vs StreamEx

BenchmarkStreamConcat.java

package com.soebes.performance.streams;

import org.openjdk.jmh.annotations.*;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
import one.util.streamex.*;


@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@Warmup(iterations = 5, time = 500, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
@Fork(3)
@State(Scope.Thread)
public class BenchmarkStreamConcat {


  @Benchmark
  public List<Element> with_new_arraylist(Container content) throws InterruptedException {
    return content.getFancyStuffs().stream().flatMap(item -> {
      ArrayList<Element> objects = new ArrayList<>();
      objects.add(item.getElement());
      objects.addAll(item.getElements());
      return objects.stream();
    }).collect(Collectors.toList());

  }

  @Benchmark
  public List<Element> with_stream_concat(Container content) {
    return content.getFancyStuffs()
      .stream()
      .flatMap(fs -> Stream.concat(Stream.of(fs.getElement()), fs.getElements().stream()))
      .collect(Collectors.toList());

  }

  @Benchmark
  public List<Element> with_streamex_complete(Container content) {
    return StreamEx.of(content.getFancyStuffs())
      .flatMap(fs -> StreamEx.of(fs.getElements()).prepend(fs.getElement()))
      .toList();
  }

  @State(Scope.Thread)
  public static class Container {
    private List<FancyStuff> fancyStuffs;

    public Container() {
      this.fancyStuffs = Collections.emptyList();
    }

    @Param({"50", "100", "1000", "2000", "5000"})
    int count;

    @Setup(Level.Trial)
    public void setup() {
      fancyStuffs = IntStream.rangeClosed(1, count)
        .mapToObj(i -> new FancyStuff(new Element(i + 1), createList(i)))
        .collect(Collectors.toList());
    }

    @TearDown(Level.Trial)
    public void tearDown() {
      this.fancyStuffs = Collections.emptyList();
    }

    private List<Element> createList(int factor) {
      return IntStream.rangeClosed(2, 50)
        .mapToObj(i -> new Element(i * factor))
        .collect(Collectors.toList());
    }

    public List<FancyStuff> getFancyStuffs() {
      return fancyStuffs;
    }
  }

}