通过id对java list集合进行分组之后返回到同一个list集合中

可以使用Java 8中的Stream API来对List集合进行分组，然后将分组后的元素添加到同一个List集合中。下面是一个示例代码：

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class GroupList {
    public static void main(String[] args) {
        List<Person> persons = new ArrayList<>();
        persons.add(new Person(1, "Alice"));
        persons.add(new Person(2, "Bob"));
        persons.add(new Person(3, "Charlie"));
        persons.add(new Person(4, "David"));
        persons.add(new Person(5, "Eva"));
        persons.add(new Person(6, "Frank"));
        persons.add(new Person(7, "George"));
        persons.add(new Person(8, "Henry"));
        persons.add(new Person(9, "Ivy"));
        persons.add(new Person(10, "Jack"));

        // 将Person对象按照id进行分组
        Map<Integer, List<Person>> groupedMap = persons.stream().collect(Collectors.groupingBy(Person::getId));

        // 将分组后的元素添加到同一个List集合中
        List<Person> result = new ArrayList<>();
        groupedMap.values().forEach(result::addAll);

        System.out.println(result);
    }
}

class Person {
    private int id;
    private String name;

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

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

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

运行结果如下：

[Person{id=1, name='Alice'}, Person{id=2, name='Bob'}, Person{id=3, name='Charlie'}, Person{id=4, name='David'}, Person{id=5, name='Eva'}, Person{id=6, name='Frank'}, Person{id=7, name='George'}, Person{id=8, name='Henry'}, Person{id=9, name='Ivy'}, Person{id=10, name='Jack'}]