使用通配符的Java集合

public void printList(List<?> list) {
    for (Object obj : list) {
        System.out.println(obj);
    }
}

List<String> stringList = Arrays.asList("hello", "world");
List<Integer> intList = Arrays.asList(1, 2, 3);
printList(stringList);
printList(intList);

public void printMap(Map<?, ?> map) {
    for (Map.Entry<?, ?> entry : map.entrySet()) {
        System.out.println(entry.getKey() + " : " + entry.getValue());
    }
}

Map<String, Integer> stringIntMap = new HashMap<>();
stringIntMap.put("hello", 1);
stringIntMap.put("world", 2);
printMap(stringIntMap);