Java 8 Lambda 表达式学习

public class LambdaDemo {

    private List<Id> ids;

    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    static class Student{
        private String name;
        private String city;
    }

    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    static class Id{
        private Integer id;
    }


    /**
     * 遍历List和Map
     */
    public static void listAndMapForEach() {

        List<String> list = new ArrayList<>();
        list.add("张三");
        list.add("李四");
        list.add("王五");
        list.forEach(System.out::println);


        Map<String, String> map = new HashMap<>();
        map.put("name", "zjc");
        map.put("city", "广州");
        map.forEach((k, v) -> System.out.println(k + " : " + v));

    }

    /**
     * List 转为 Map
     */
    public static void listToMap(){

        Student t1 = new Student("zjc", "GZ");
        Student t2 = new Student("lisi", "BJ");
        Student t3 = new Student("zjc", "SZ");
        List<Student> studentList = new ArrayList<>();
        studentList.add(t1);
        studentList.add(t2);
        studentList.add(t3);

        // 1. 简单的合并, (k1,k2) -> k1) 解决k重复，导致报错问题
        /*Map<String, Student> studentMap = studentList.stream().collect(
                Collectors.toMap(Student::getName, Function.identity(),(k1,k2) -> k1));

        studentMap.forEach((k,v) -> System.out.println(k+" : "+v));*/

        // 2. 同一个主键 合并到集合中
        Map<String, List<Student>> studentMap = studentList.stream().collect(Collectors.groupingBy(Student::getName));

        studentMap.forEach((k,v) -> System.out.println(k+" : "+v));


    }

    public static void setToObjectList(){

        Set<Integer> idSet = new HashSet<>();
        idSet.add(1);
        idSet.add(2);
        List<Id> ids = idSet.stream().map(Id::new)
                .collect(Collectors.toList());

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

    }

    public static void main(String[] args) {

//        listAndMapForEach();
//        listToMap();

        setToObjectList();
    }
}