Unchecked cast 'java.lang.Object' to 'java.util.List' | Jalen's Blog = Follow your heart = A happy life

出现原因，实际应用时 map 集合中存在多个键值对，而由于每个键对应的值为不同类型，当存在一个值的类型为 List 时，在接收时做强制转换会出现此警告
出错代码举例

	Map<String,Object> repeatMap = checkAndRemoveRepeatRecords(dataList);

	int dataRepeatCounter = (int)repeatMap.get("dataRepeatCounter");
	List<String[]> dataList = (List<String[]>)repeatMap.get("dataList");

修改方法 1（加 unchecked 注解）

	public class Test {
	public static void main(String[] args) {
	test1();
	}

	@SuppressWarnings("unchecked")
	private static void test1() {
	Map<String, Object> map_original_foo = new HashMap<>();
	Map<String, Integer> map_original_son = new HashMap<>();
	map_original_son.put("a", 1);
	map_original_son.put("b", 2);
	map_original_son.put("c", 3);

	map_original_foo.put("aa", map_original_son);

	Map<String, Integer> map_current_son = (Map<String, Integer>) map_original_foo.get("aa");
	System.out.println(map_current_son);
	}
	}

修改方法 2（类型检查）

	public class Test {
	public static void main(String[] args) {
	testMap();
	testList();
	}

	private static void testMap() {
	Map<String, Object> map_original_foo = new HashMap<>();
	Map<String, Integer> map_original_son = new HashMap<>();
	map_original_son.put("a", 1);
	map_original_son.put("b", 2);
	map_original_son.put("c", 3);

	map_original_foo.put("aa", map_original_son);

	if (map_original_foo.get("aa") instanceof Map<?, ?>) {
	Map<?, ?> map_current_foo = (Map<?, ?>) map_original_foo.get("aa");
	Class keyClass = map_current_foo.entrySet().stream().findFirst().map(entry -> entry.getKey().getClass()).orElse(null);
	Class valueClass = map_current_foo.entrySet().stream().findFirst().map(entry -> entry.getValue().getClass()).orElse(null);

	if (String.class.equals(keyClass) && Integer.class.equals(valueClass)) {
	Map<String, Integer> map_current_son = new HashMap<>();
	for (Map.Entry entry : map_current_foo.entrySet()) {
	String key = (String) entry.getKey();
	Integer value = (Integer) entry.getValue();
	map_current_son.put(key, value);
	}
	System.out.println(map_current_son);
	}
	}
	}

	private static void testList() {
	Map<String, Object> map_original_foo = new HashMap<>();
	List<String> list_original_son = new ArrayList<>();
	list_original_son.add("aa");
	list_original_son.add("bb");
	list_original_son.add("cc");
	map_original_foo.put("dd", list_original_son);

	if (map_original_foo.get("dd") instanceof List<?>) {
	List<?> temp_list = (List<?>) map_original_foo.get("dd");
	Class valueClass = temp_list.stream().findFirst().map(Object::getClass).orElse(null);
	if (String.class.equals(valueClass)) {
	List<String> list_current_son = new ArrayList<>();
	for (Object s: temp_list) {
	String value = (String) s;
	list_current_son.add(value);
	}
	System.out.println(list_current_son);
	}
	}
	}
	}