Java之Stream笔记

Stream流的创建方法

    public static void main(String[] args) {

        Stream stream1 = Stream.of("hello","world","hello stream");

        String[] myArray = new String[]{"hello","world","hello stream"};
        Stream stream2 = Arrays.stream(myArray);
        Stream stream3 = Stream.of(myArray);

        List<String> list = Arrays.asList(myArray);
        Stream stream4 = list.stream();


        stream1.forEach(System.out::println);

        stream2.forEach(System.out::println);

        stream3.forEach(System.out::println);
        
        stream4.forEach(System.out::println);

    }

Stream的基础使用：

    public static void main(String[] args) {
        IntStream.range(1,10).forEach(System.out::println);

        //我来算一算 1+...+100 等于多少
        IntStream.rangeClosed(1,100).reduce(Integer::sum).ifPresent(System.out::print);
    }

函数式编程传递的是一种行为，根据传递的行为处理数据

    public static void main(String[] args) {

        Stream<java.lang.String> stream = Stream.of("hello","world","hello stream");

        String[]  list =  stream.toArray(length -> new String[length]);

        for (int i = 0 ;i<list.length;i++){
            System.out.println(list[i]);
        }
    }

<A> A[] toArray(IntFunction<A[]> generator);方法接收一个IntFunction<A[]>类型函数式接口，在IntFunction<A[]>中接收一个int 返回一个R 也就是返回A[]，文档中有说明，【The generator function takes an integer, which is the size of the desired array 】这个int值就是这个流中array的size。

所以这个lambada表达式是：

String[] list = stream.toArray(length -> new String[length]);

看到new Stirng[length]，我们明显可以使用构造方法引用：

String[] list2 = stream.toArray(String[]::new);

    public static void main(String[] args) {

        Stream<java.lang.String> stream = Stream.of("hello","world","hello stream");

//        String[]  list =  stream.toArray(length -> new String[length]);
//        for (int i = 0 ;i<list.length;i++){
//            System.out.println(list[i]);
//        }

        //等价于：
        String[] list2 = stream.toArray(String[]::new);
        for (int i = 0 ;i < list2.length;i++){
            System.out.println(list2[i]);
        }
    }