Guardian-Development

public class FileLineReader implements Iterable<String> {

        private final File inputFile;

        FileLineReader(File inputFile) {
            this.inputFile = inputFile;
        }

        @Override
        public Iterator<String> iterator() {

Guardian-Development

  public final class DataSource<T> {

      private Iterator<T> source;

      DataSource(Iterator<T> source) {
          this.source = source;
      }

      public <D> Tranformation<T, D> transform(Tranformation<T, D> transformer) {
          return new Tranformation<>(source, transformer);

Guardian-Development

public interface ApplyFunction<T, D> {
      D apply(T input);
  }

  public final class Tranformation<T, D> implements Iterator<D> {

      private final Iterator<T> source;
      private final ApplyFunction<T, D> transformer;

      Tranformation(Iterator<T> source, ApplyFunction<T, D> transformer) {

Guardian-Development

  public interface ApplyResult<T> {
      void apply(T message);
  }

  public final class Sink<T> {

      private final Iterator<T> source;
      private final ApplyResult<T> sink;

      Sink(Iterator<T> source, ApplyResult<T> sink) {

Guardian-Development

public class App {

    public static void main(String[] args) {
        Sink<Double> sink = new DataSource<>(Arrays.asList("1", "2", "3", "4").iterator())
                .transform(s -> Integer.parseInt(s))
                .transform(i -> (double) i)
                .sink(i -> System.out.println("The result is: " + i));

        // prints 1.0, 2.0, 3.0, 4.0
        sink.execute();