1. Stream流的作用

   结合Lambda表达式，简化集合、数组操作

2. Stream使用步骤

   • 获取Steam流对象
   • 使用中间方法处理数据
   • 使用终结方法处理数据

3. 如何获取Stream流对象

   • 单列集合：Collection中的默认方法stream
   • 双列集合：通过keySet，或者enterSet
   • 数组：Arrays.stream(arr1)
   • 零散数据：stream.of(1,2,3,4)

4. 常见方法

   中间方法：filter、limit、skip、distinct、concat、map

   终结方法：forEach、count、collect（可以收集list,set,map）

三个练习题

1. 过滤奇数

List<Integer> collect = Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
            .filter(item -> item % 2 == 0)
            .collect(Collectors.toList());

1. String转map

ArrayList<String> strings = new ArrayList<>();
        Collections.addAll(strings, "zhangsan, 23", "lisi, 24", "wangwu, 25");
        Map<String, String> collect1 = strings.stream().filter(s -> Integer.parseInt(s.split(",")[1].trim()) >= 24)
            .collect(Collectors.toMap(
                item -> item.split(",")[0],
                item -> item.split(",")[1]
            ));
        System.out.println(collect1);

1. 收集自定义对象

class Actor{
            String name;
            Integer age;
            public Actor(String name, Integer age) {
                this.name = name;
                this.age = age;
            }

            @Override
            public String toString() {
                return "Actor{" +
                    "name='" + name + '\\'' +
                    ", age=" + age +
                    '}';
            }
        }
        ArrayList<String> actors1 = new ArrayList<>();
        actors1.add("张三三,23");
        actors1.add("李四四,32");
        actors1.add("王五五,27");
        actors1.add("赵佳,29");
        actors1.add("孙丽,31");
        actors1.add("孙丽丽,31");

        ArrayList<String> actors2 = new ArrayList<>();
        actors2.add("杨琪,26");
        actors2.add("杨萌,28");
        actors2.add("林一,25");
        actors2.add("王勇,33");
        actors2.add("陈丹,30");
        actors2.add("杨洋,24");

        Stream<String> s1 = actors1.stream().filter(s -> s.split(",")[0].length() == 3)
            .limit(2);
        Stream<String> s2 = actors2.stream().filter(s -> s.startsWith("杨"))
            .skip(1);
        List<Actor> collect = Stream.concat(s1, s2).map((item) -> {
            String name = item.split(",")[0];
            String age = item.split(",")[1];
            return new Actor(name, Integer.parseInt(age));
        }).collect(Collectors.toList());
        System.out.println(collect);