在Java中按两个字段对列表进行分组

import java.util.*;
import java.util.stream.Collectors;

public class GroupingExample {
    public static void main(String[] args) {
        // 创建对象列表
        List<MyObject> myList = Arrays.asList(
                new MyObject("A", "X"),
                new MyObject("A", "Y"),
                new MyObject("B", "X"),
                new MyObject("B", "Y"),
                new MyObject("C", "X"),
                new MyObject("C", "Y")
        );

        // 按照field1和field2对列表进行分组
        Map<String, Map<String, List<MyObject>>> groupedMap = myList.stream()
                .collect(Collectors.groupingBy(MyObject::getField1,
                        Collectors.groupingBy(MyObject::getField2)));

        // 打印分组结果
        for (Map.Entry<String, Map<String, List<MyObject>>> entry1 : groupedMap.entrySet()) {
            String field1 = entry1.getKey();
            Map<String, List<MyObject>> innerMap = entry1.getValue();
            for (Map.Entry<String, List<MyObject>> entry2 : innerMap.entrySet()) {
                String field2 = entry2.getKey();
                List<MyObject> objects = entry2.getValue();
                System.out.println("Field1: " + field1 + ", Field2: " + field2 + ", Objects: " + objects);
            }
        }
    }
}

class MyObject {
    private String field1;
    private String field2;

    public MyObject(String field1, String field2) {
        this.field1 = field1;
        this.field2 = field2;
    }

    public String getField1() {
        return field1;
    }

    public String getField2() {
        return field2;
    }

    @Override
    public String toString() {
        return "MyObject{" +
                "field1='" + field1 + '\'' +
                ", field2='" + field2 + '\'' +
                '}';
    }
}