public static void main(String[] args) {

    Map<Integer, String> map = new HashMap<>();
    map.put(10, "apple");
    map.put(20, "orange");
    map.put(30, "banana");
    map.put(40, "watermelon");
    map.put(50, "dragonfruit");
    //result中的值是map物件中的key
    List<Integer> result = new ArrayList(map.keySet());
    //result2中的值是map物件中的value
    List<String> result2 = new ArrayList(map.values());
}