Run benchmark for stream() vs parallelStream()

StreamBenchmark.java

package io.bewaremypower;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.TimeUnit;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.Level;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.OptionsBuilder;

@State(Scope.Benchmark)
public class StreamBenchmark {

  @State(Scope.Benchmark)
  public static class Input {
    public static final int N = 1000; // TODO: change the N here
    public final List<Integer> integers = new ArrayList<>();
  }

  @Setup(Level.Trial)
  public void setup(Input input) throws Exception {
    final var random = new Random();
    input.integers.clear();
    for (int i = 0; i < Input.N; i++) {
      input.integers.add(random.nextInt(1000));
    }
  }

  @Warmup(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
  @Measurement(iterations = 5, time = 500, timeUnit = TimeUnit.MILLISECONDS)
  @Benchmark
  public void testStream(Input input) {
    final var ignored = input.integers.stream().map(__ -> Integer.toString(__)).toList();
  }

  @Warmup(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
  @Measurement(iterations = 5, time = 500, timeUnit = TimeUnit.MILLISECONDS)
  @Benchmark
  public void testParallelStream(Input input) {
    final var ignored = input.integers.parallelStream().map(__ -> Integer.toString(__)).toList();
  }

  public static void main(String[] args) throws RunnerException {
    final var opt =
        new OptionsBuilder().include(StreamBenchmark.class.getSimpleName()).forks(1).build();
    new Runner(opt).run();
  }
}