Demo of how sequential iterators behave with parallel streams in Java 8

TestIterators.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

public class TestIterators {
  public static void main(String[] args) {
    List<String> strings =
      Arrays.asList("ab", "cdef", "g", "hijk", "lmn", "opqr", "stu", "vwx", "yz");
    List<Integer> lengths;

    lengths = new Samples(strings).parallelStream()
      .map((s) -> {
        System.out.printf("Thread %s: Processing %s\n", Thread.currentThread().toString(), s);

        return s.length();
      })
      .collect(Collectors.toList());

    System.out.println(lengths);
  }

  private static class Samples
  implements Iterable<String> {
    private final List<String> samples;

    private Samples(List<String> samples) {
      this.samples = new ArrayList<>(samples);
    }

    @Override
    public java.util.Iterator<String> iterator() {
      return new Iterator();
    }

    public Stream<String> parallelStream() {
      return StreamSupport.stream(this.spliterator(), true);
    }

    private class Iterator
    implements java.util.Iterator<String> {
      private int index;

      public Iterator() {
        this.index = 0;
      }

      @Override
      public boolean hasNext() {
        return (this.index < (Samples.this.samples.size() - 1));
      }

      @Override
      public String next() {
        final String nextString = Samples.this.samples.get(this.index++);

        System.out.println("Requesting " + nextString);
        try {
          Thread.sleep(1000);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }

        return nextString;
      }
    }
  }
}