List< Integer > list = IntStream.range(0, 10).boxed().collect(Collectors.toList());
            

    List list = Arrays.asList(1, 4, 5);
    List ls = IntStream.range(0, list.size()).mapToObj(i -> 2*list.get(i)).collect(Collectors.toList());

    List list = Arrays.asList(1, 4, 5);
    List ls = list.stream().map(i -> 2*i).collect(Collectors.toList());

    // Though it is not as elegant as Haskell
    // map (*2) [1, 4, 5]
            

    List list = Arrays.toList(1, 2, 3);
    Optional sum = list.stream().reduce((x, y) -> x + y);
    sum.ifPresent(System.out::println);
    
    Integer sum = list.stream().reduce(0, (x, y) -> x + y);

            

    List ls = Arrays.asList("file.htmlkk", "file.html", "kk.html_33", ".html", "html");
    List fls = ls.stream().filter( s -> FileType.isHtml(s) ).collect(Collectors.toList());

    List ls3 = Arrays.asList(1, 2, 3, 4);
    Set set = ls3.stream().filter(i -> i >= 2).collect(Collectors.toSet());
    p(set);
    

    Optional sum = list.stream().reduce(Double::sum);
    sum.ifPresent(System.out::println);

    Integer[] array = {1, 2, 3, 4};
    List listInt = Arrays.asList(array);

    // list filter
    List< Integer> leftList = listInt.stream().filter(x-> x < 3).collect(Collectors.toList());
    List< Integer> rightList = listInt.stream().filter(x-> x > 3).collect(Collectors.toList());

    Aron.printList(leftList);
    Aron.printList(rightList);

    // list forEach
    leftList.forEach(System.out::println);
    leftList.forEach(x->System.out.println(x));

    // HashMap filter
    Map< Integer, Integer> map = new HashMap< Integer, Integer>();
    map.put(1, 4);
    map.put(2, 5);
    map.put(3, 7);

    Map< Integer, Integer> newMap1 = map.entrySet().parallelStream()
                                                .filter(e->e.getValue() > 1)
                                                .collect(Collectors.toMap(e->e.getKey(), e->e.getValue()));

    Aron.printMap(newMap1);

    Map< Integer, Integer> newMap2 = map.entrySet().stream()
                                                 .filter(e->e.getValue() > 1)
                                                 .collect(Collectors.toMap(e->e.getKey(), e->e.getValue()));
    Aron.printMap(newMap2);

    // list of String to list of Integer
    String[] arrStr = {"0", "1", "2", "3"}; 
    List< String> list1 = Arrays.asList(arrStr);
    List< Integer> strIntList = list1.stream().map(Integer::parseInt).collect(Collectors.toList());
    Aron.printList(strIntList);