java8 list turn Map error Collectors.toMap :: results in "Non-static method can not be refernced from static context" java8 - List into Map, grouping, filtering, and summation operation

1. Problem: java8 list turn Map

报错Collectors.toMap :: results in "Non-static method cannot be refernced from static context"

 

 

 Solution: The second argument to function

 

 

 The reason: Collectors.toMap received as a function parameter

2. Repeat solve key problems:

        Map<String,String> map2=list.stream().collect(Collectors.toMap(Person::getName,o->"",(key1,key2)->key2));

Output: {cc =, bb =, aa22 =, aa11 =}

3.value as the object itself, note that the generic map to Person

Person

public  class Person {
    private String id;
    private String name;

    public  String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public Person(String name) {
        this.name = name;
    }

    public Person(String id, String name) {
        this.id = id;
        this.name = name;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                '}';
    }

 

map

List<Person> list=new ArrayList<>();

list.add(new Person("aa","aa11"));
list.add(new Person("bb",""));
list.add(new Person("aa","aa22"));
list.add(new Person("cc",""));

Map<String,Person> map2=list.stream().collect(Collectors.toMap(o->o.getId(),o->o,(key1,key2)->key2));//重复时取后面的

//Map<String,Person> map2=list.stream().collect(Collectors.toMap(o->o.getId(), Function.identity(),(key1, key2)->key2));//优雅写法

System.out.println(map2);

输出：{cc=Person{id='cc', name=''}, bb=Person{id='bb', name=''}, aa=Person{id='aa', name='aa22'}}

 4. Sort by:

        Map<String,String> map2=list.stream().collect(Collectors.toMap(Person::getId,Person::getName ,(key1, key2)->key2,TreeMap<String,String>::new));

Output {aa = aa22, bb =, cc =}

Other: java8 - List into the Map, packet filtering, and summation operations