Question

class Person {
    private String sex;
    private List<String> nameList;

    public Person(String sex, String name) {
        this.sex = sex;
        this.nameList = new ArrayList<>();
        this.nameList.add(name);
    }


    public Person(String sex, List<String> nameList) {
        this.sex = sex;
        this.nameList = nameList;
    }

}

public static void main(String[] args) {
    Person p1 = new Person("M", "name1");
    Person p2 = new Person("M", "name2");
    Person p3 = new Person("F", "name3");
    Person p4 = new Person("F", "name4");
    Person p5 = new Person("F", "name5");

    List<Person> ps = Arrays.asList(p1, p2, p3, p4, p5);

    // sex --> Person
    Map<String, Person> map1 = new HashMap<>();
    ps.forEach(p -> {
        Person pp = map1.get(p.getSex());
        if (pp == null) {
            pp = new Person(p.getSex(), p.getNameList());
            map1.put(p.getSex(), pp);
        } else {
            pp.getNameList().addAll(p.getNameList());
        }
    });
    System.out.println(map1);

    Map<String, Person> map2 = ps.stream().collect(/* how to write here*/);
    System.err.println(map2);
}

我希望用户ps.stream().collect()解决此问题，例如主()

谢谢！

Answer 1

创建人物姓名（键）到人物（值）的地图

Collectors.toMap(p -> p.getName(), p -> p);

Answer 2

我知道答案;

product category

如何使用java8来收集这张地图

2 个答案: