怎样才能实例化的Java地图的数组？ [英] How does one instantiate an array of maps in Java?

问题描述

我可以使用泛型指定地图类型声明映射的数组：

I can declare an array of maps using generics to specify the map type:

private Map<String, Integer>[] myMaps;

不过，我想不出如何正确实例吧：

However, I can't figure out how to instantiate it properly:

myMaps = new HashMap<String, Integer>[count]; // gives "generic array creation" error
myMaps = new HashMap[count]; // gives an "unchecked or unsafe operation" warning
myMaps = (Map<String, Integer>[])new HashMap[count]; // also gives warning

我怎么能实例没有得到一个编译器错误或警告这阵地图？

How can I instantiate this array of maps without getting a compiler error or warning?

更新：

感谢大家的回复。我结束了名单的建议下去。

Thank you all for your replies. I ended up going with the List suggestion.

推荐答案

不是严格意义上的回答你的问题，但你有没有考虑使用列表呢？

Not strictly an answer to your question, but have you considered using a List instead?

List<Map<String,Integer>> maps = new ArrayList<Map<String,Integer>>();
...
maps.add(new HashMap<String,Integer>());

似乎工作就好了。

seems to work just fine.

请参阅 Java理论与实践：泛型陷阱获取详细的解释，为什么混合泛型数组是不鼓励。

See Java theory and practice: Generics gotchas for a detailed explanation of why mixing arrays with generics is discouraged.

由于在评论中提到的德鲁，它可能是更好的使用的收藏接口而不是列表。这可能会派上用场，如果你需要更改为设置或收藏其他子接口之一。例如：code：

As mentioned by Drew in the comments, it might be even better to use the Collection interface instead of List. This might come in handy if you ever need to change to a Set, or one of the other subinterfaces of Collection. Example code:

Collection<Map<String,Integer>> maps = new HashSet<Map<String,Integer>>();
...
maps.add(new HashMap<String,Integer>());

从这个出发点，你只需要修改 HashSet的到的ArrayList ，的PriorityQueue ，或者任何其它类实现收藏。

From this starting point, you'd only need to change HashSet to ArrayList, PriorityQueue, or any other class that implements Collection.

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