有没有一种方法来实现LinkedHashMap的数组? [英] Is there a way to implement an array of LinkedHashMap?

问题描述

我正在尝试实现LinkedHashMap的数组，但我不知道是否有可能...

I am trying to implement an array of LinkedHashMap but I don't know if it's possible...

目前，我的代码如下:

public class LHMap {

    public static void main(String[] args) {

     LinkedHashMap<String, Integer>[] map = null;

  for (int i = 0; i < 5; i++) {
         map[i] = new LinkedHashMap<String, Integer>();
  }

  map[0].put("a", 0);
  System.out.println(map[0].get("a"));

 }
}

System.out.println(extracted(map)[0].get("a"));

返回"NullPointerException" ...

returns a "NullPointerException"...

您知道如何实现吗?

1.擦除extract()，2.表格->数组

EDIT : 1. erase extracted(), 2. table->array

推荐答案

我不知道您的 extracted()方法正在尝试做什么.您将得到一个 NullPointerException ，因为您是将 map 传递到 extracted 中，然后立即将其返回.在您的示例中，您要传入 null ，然后将其返回.在空数组上找不到第i个 下标(或任何下标).

I don't know what your extracted() method is trying to do. You're getting a NullPointerException because you're passing map into extracted and then you're returning it immediately. In your example, you're passing in null and then returning it. You can't find the i^th subscript (or any subscript) on a null array.

List 可以代替 LinkedHashMap 的数组吗?

List<Map<String, Integer>> listOfMaps = new ArrayList<Map<String, Integer>>();

for(int i = 0; i < 5; i++) {
   listOfMaps.add(new LinkedHashMap<String, Integer>());
}

listOfMaps.get(0).put("a", 0);
System.out.println(listOfMaps.get(0).get("a"));

编辑

顺便说一句，您不能使用泛型实例化数组.如果您需要类型安全性，建议您与列表一起使用.否则，您必须解决以下问题:

You cannot instantiate an array with generics, by the way. I'd suggest going with the list if you want the type-safety. Otherwise you'd have to make do with:

LinkedHashMap<String, Integer>[] map = new LinkedHashMap[5];

但是，这会给您警告.

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