J8.java

private Function<Color, Color> filter;

    @Test
    public void j8Test() throws Exception {

        Optional<Integer> optional = stream().filter((a) -> a > 10).findFirst();
        optional.


        Integer result = optional.map(i -> i * i).orElse(-1);
        System.out.println(result);

        Map<Integer, List<Integer>> grouppedBy = stream().collect(groupingBy(Function.<Integer>identity()));

        System.out.println(grouppedBy);
        Map<Integer, Optional<Integer>> grouppedAndSummed = stream().collect(groupingBy(Function.<Integer>identity(), reducing((Integer a, Integer b) -> a + b)));
        System.out.println(grouppedAndSummed);

        Integer sum = stream().collect(Collectors.summingInt((a) -> a));
        System.out.println(sum);

        Double avg = stream().collect(Collectors.averagingInt((a) -> a));
        System.out.println(avg);

        Integer product = stream().collect(Collectors.reducing(1, (a, b) -> a * b));
        System.out.println(product);

        Integer product2 = stream().reduce(1, (a, b) -> a * b);
        System.out.println(product2);

        Integer sumOfages = personStream().collect(Collectors.summingInt((Person p) -> p.age));
        System.out.println(sumOfages);

        Integer sumOfages2 = personStream().collect(Collectors.summingInt(Person::getAge));
        System.out.println(sumOfages2);

        Function<Person,Integer> f = (Person p) -> p.age;
        ToIntFunction<Person> ff = (Person p) -> p.age;

        Integer sumOfages3 = personStream().collect(Collectors.summingInt(ff));
        System.out.println(sumOfages3);

        Integer sumOfages4 = personStream().mapToInt(Person::getAge).sum();
        System.out.println(sumOfages4);

        personStream().mapToInt(Person::getAge).sum();

//        Arrays.asList(new Character('a')).stream().
        Stream<Character> characterStream = "aasdqweasd".chars().mapToObj(i -> Character.valueOf((char) i));


    }

    private Stream<Person> personStream() {
        return Arrays.asList(new Person(1), new Person(2)).stream();
    }

    class Person {
        public int age;

        Person(int age) {
            this.age = age;
        }

        public int getAge() {
            return age;
        }
    }


    private Stream<Integer> stream() {
        return Arrays.asList(1, 2, 3, 4, 3, 4, 2, 3, 4).stream();
    }

    public void setFilters(final Function<Color, Color>... filters) {
        filter =
                Stream.of(filters)
                        .reduce((filter, next) -> filter.compose(next))
                        .orElse(color -> color);
    }