class NumSupplier implements Supplier<Long> {

        long value = 0;

        public Long get() {

            this.value = this.value + 1;

            return this.value;

        }

    }

    /**

     * 无穷集合

     */

    public static void numTest(){

        Stream<Long> natural = Stream.generate(new NumSupplier());

        natural.map((x) -> {

            return x * x;

        }).skip(2).limit(20).forEach(System.out::println);

        //转list stream has already been operated upon or closed
        List<Long> collect = natural.collect(Collectors.toList());
    }

    /**

     * Stream Test

     */

    public static void streamTest(){

        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        Stream<Integer> stream = numbers.stream();

        stream.filter(a->{

            a += 10;

            return a > 15;

        }).map(a -> {

            return a * a;

        }).forEach(System.out::println);

    }