如何将具有相同键的两个 HashMap 中的值（不同数据类型）放入新的第三个 HashMap？

Question

我需要根据 PeopleAndNumbers 和 PeopleAndGroups 哈希图中的值制作第三个 HashMap。 但是第三个 HashMap 将只有 3 个组作为键，而该组中的人的总数作为值。

（还值得注意的是，前两个地图中的键是相同的。）

以下是前两张地图的内容：

PeopleAndNumbers: {p1=1, p2=3, p3=2, p4=3, p5=1, p6=2}

PeopleAndGroups： {p1=GroupA, p2=GroupB, p3=GroupC, p4=GroupB, p5=GroupC, p6=GroupA}

我需要制作第三个 HashMap 打印出来是这样的：

组合地图： {GroupA=3, GroupB=6, GroupC=3}

到目前为止，代码如下所示：

import java.util.HashMap;

public class HashmapTest {

        public static void main(String[] args) {
            
            HashMap<String, Integer> PeopleAndNumbers = new HashMap<String, Integer>();

            HashMap<String, String> PeopleAndGroups = new HashMap<String, String>();

            PeopleAndNumbers.put("p1", 1);
            PeopleAndNumbers.put("p2", 3);
            PeopleAndNumbers.put("p3", 2);
            PeopleAndNumbers.put("p4", 3);
            PeopleAndNumbers.put("p5", 1);
            PeopleAndNumbers.put("p6", 2);

            PeopleAndGroups.put("p1","GroupA");
            PeopleAndGroups.put("p2","GroupB");
            PeopleAndGroups.put("p3","GroupC");
            PeopleAndGroups.put("p4","GroupB");
            PeopleAndGroups.put("p5","GroupC");
            PeopleAndGroups.put("p6","GroupA");

            System.out.println(PeopleAndNumbers);
            System.out.println(PeopleAndGroups);

            HashMap<String, Integer> CombineMap = new HashMap<String, Integer>();

            //Insert method to do this here, How would I go about this?

            System.out.println("Expected Output for CombineMap should be");
            System.out.println("{GroupA=3, GroupB=6, GroupC=3}");

            System.out.println(CombineMap);
        }
    }

Answer 1

没有流：

for (Map.Entry<String, Integer> entry : PeopleAndNumbers.entrySet()) { //or iterate over peaopleAndGroups..
  CombineMap.put(PeopleAndGroups.get(entry.getKey()), entry.getValue()); // put replaces (if) existing key 
}

Answer 2

如果我理解正确，您想按组对数字求和，使用常用键加入它们。 如果是这样，您可以使用流很容易地做到这一点：

Map<String, Integer> combined = PeopleAndGroups.entrySet()
        .stream()
        .collect(Collectors.groupingBy(e -> e.getValue(),
                Collectors.summingInt(e -> PeopleAndNumbers.get(e.getKey()))));