相关疑难解决方法(0)

我想通过一个分类器使用Java 8 Stream和Group,但是有多个Collector函数.因此,在分组时,例如计算一个场(或可能是另一个场)的平均值和总和.

我尝试用一​​个例子来简化这一点:

public void test() {
    List<Person> persons = new ArrayList<>();
    persons.add(new Person("Person One", 1, 18));
    persons.add(new Person("Person Two", 1, 20));
    persons.add(new Person("Person Three", 1, 30));
    persons.add(new Person("Person Four", 2, 30));
    persons.add(new Person("Person Five", 2, 29));
    persons.add(new Person("Person Six", 3, 18));

    Map<Integer, Data> result = persons.stream().collect(
            groupingBy(person -> person.group, multiCollector)
    );
}

class Person {
    String name;
    int group;
    int age;

    // Contructor, getter and setter
}

class Data {
    long average;
    long sum;

    public Data(long average, long …