使用泛型对元素列表进行分组

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

public class GroupingExample {
    public static <T, K> Map<K, List<T>> groupBy(List<T> list, GroupingFunction<T, K> groupingFunction) {
        Map<K, List<T>> groupedMap = new HashMap<>();
        for (T element : list) {
            K key = groupingFunction.apply(element);
            if (!groupedMap.containsKey(key)) {
                groupedMap.put(key, new ArrayList<>());
            }
            groupedMap.get(key).add(element);
        }
        return groupedMap;
    }

    public static void main(String[] args) {
        List<String> fruits = List.of("apple", "banana", "orange", "apple", "grape", "banana");
        Map<String, List<String>> groupedFruits = groupBy(fruits, String::toUpperCase);
        System.out.println(groupedFruits);
    }
}

interface GroupingFunction<T, K> {
    K apply(T element);
}