有没有办法实现LinkedHashMap的数组？

发布于 2024-09-30 21:17:21 字数 561 浏览 7 评论 0原文

我正在尝试实现 LinkedHashMap 数组，但我不知道是否可能......

目前我的代码如下所示：

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"));

returns a "NullPointerException"...

您知道如何实施吗？

编辑：1.擦除提取（），2.表->数组

原文

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

For the moment my code looks like as follows :

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"));

returns a "NullPointerException"...

Have you got any idea how to implement this?

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

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甜味拾荒者 2024-10-07 21:17:21

我不知道您的 extracted() 方法想要做什么。您收到 NullPointerException 是因为您将 map 传递到 extracted 中，然后立即返回它。在您的示例中，您传入 null 然后返回它。您无法在空数组上找到第 i^th 下标（或任何下标）。

List 可以代替 LinkedHashMap 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

顺便说一下，你不能用泛型实例化数组。如果您想要类型安全，我建议您使用该列表。否则你就不得不凑合：

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

但是，这会给你警告。

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.

Instead of an array of LinkedHashMap, would a List work?

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"));

EDIT

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];

This will give you warnings, however.

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蒗幽 2024-10-07 21:17:21

map[i] = new LinkedHashMap<String, Integer>();

这将导致 NPE，因为您从不初始化映射，或者更确切地说，您显式地将其初始化为 NULL：

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

编辑：

您需要实例化数组，例如：

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

尽管您会收到该代码的“未经检查的转换”警告。另请检查此以了解通用数组创建问题（感谢那些指出它的人出去）。

map[i] = new LinkedHashMap<String, Integer>();

That will cause an NPE because you never initialize map, or rather, you explicitly initialize it to NULL:

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

EDIT:

You need to instantiate the array, e.g.:

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

Although you'll get an "unchecked conversion" warning with that code. Also check this for the generic array creation issue (thanks for those who pointed it out).

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