在Collectors.toMap中获取密钥

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

public class Main {
    public static void main(String[] args) {
        List<String> fruits = Arrays.asList("apple", "banana", "orange");

        // 使用Lambda表达式获取键
        Map<String, Integer> map1 = fruits.stream()
                .collect(Collectors.toMap(fruit -> fruit, String::length));
        System.out.println(map1);

        // 使用方法引用获取键
        Map<String, Integer> map2 = fruits.stream()
                .collect(Collectors.toMap(Function.identity(), String::length));
        System.out.println(map2);
    }
}

{orange=6, banana=6, apple=5}
{orange=6, banana=6, apple=5}