java - 类型安全 : The expression of type Map[] needs unchecked conversion to conform to Map[]

Question

我有以下两行:

Map<String,Object>[] IEXDivMap = null;       

IEXDivMap =  new Map[IEXJsonArray.length()];

并收到警告:

The expression of type Map[] needs unchecked conversion to conform to Map<String,Object>[]

有办法解决吗？

更新:

有人在评论中问我为什么我们首先需要一个 Map 数组。我们正在获取一系列 HashMap 并将每个 HashMap 放置在 map 数组中。代码如下:

@SuppressWarnings("unchecked")
public static Map<String,Object>[] getDiv(String ticker) {
    Map<String,Object>[] IEXDivMap = null;
    try{
        String url = "https://api.IEXtrading.com/1.0/stock/" + ticker + "/dividends/1y"; 
        URL obj = new URL(url);   

        HttpURLConnection con = (HttpURLConnection) obj.openConnection();       
        con.setRequestMethod("GET");
        int responseCode = con.getResponseCode();
        if(responseCode == 404){
            System.out.println("Ticker " + ticker + " NOT FOUND in getDiv()!");
            return IEXDivMap;                
        }else if (responseCode != 200){
            System.out.println("IEX Printing All Response Header for URL: " + obj.toString() + "\n");
            Map<String, List<String>> map = con.getHeaderFields();            
            for(Map.Entry<String, List<String>> entry : map.entrySet()) {
                System.out.println("IEX " + entry.getKey() + " : " + entry.getValue());
            }
        }

        BufferedReader in = new BufferedReader(new InputStreamReader(con.getInputStream()));
        String inputLine;
        StringBuilder response = new StringBuilder();

        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine);             
        }
        in.close();

        JSONArray IEXJsonArray = new JSONArray(response.toString());        
        IEXDivMap = new Map[IEXJsonArray.length()];

        for (int i = 0; i < IEXJsonArray.length(); i++) {
            IEXDivMap[i] = new HashMap<String,Object>();
            JSONObject IEXJsonObject = IEXJsonArray.getJSONObject(i);

            IEXDivMap[i].put("exDate",IEXJsonObject.getString("exDate"));
            IEXDivMap[i].put("amount",IEXJsonObject.getString("amount"));

            //System.out.println(IEXDivMap[i]);
            System.out.println(IEXDivMap[i].get("exDate") + " 0  " + IEXDivMap[i].get("amount"));
        }
    }catch(Exception e){
        System.out.println("FATAL ERROR: Something went wrong in getDiv " + e.getMessage());
        System.exit(0);
    }
    return IEXDivMap; 
}

Answer 1

不幸的是，不可能以干净的方式解决这个问题。

干净的解决方案是创建通用数组，但由于类型删除，这是不可能的。

为什么禁止创建泛型数组？

考虑以下数组示例:

Object[] arr = new String[1];
arr[0] = 10;

结果是ArrayStoreException。

现在假设允许创建通用数组:

Map<String, String>[] map = new Map<>[1]; // This is illegal
Object[] objects = map;
objects[0] = new HashMap<Integer, Integer>(); // No ArrayStoreException

编译器警告人们可以将任何Map放入数组中，并且编译器和运行时都无法检查它。因此发出警告

解决方法？

引用Java generics faq你可以使用:

• array of raw type
• array of unbounded wildcard parameterized type
• collection instead of array

<小时/>

我个人强烈建议您考虑使用列表:

List<Map<String, Object>> list = new ArrayList<>();