java：（String []）List.toArray（）给出了ClassCastException [英] java: (String[])List.toArray() gives ClassCastException

问题描述

以下代码（在android中运行）总是在第3行给出一个ClassCastException：

The following code (run in android) always gives me a ClassCastException in the 3rd line:

final String[] v1 = i18nCategory.translation.get(id);
final ArrayList<String> v2 = new ArrayList<String>(Arrays.asList(v1));
String[] v3 = (String[])v2.toArray();

当v2是Object [0]时以及当其中有字符串时也会发生这种情况。
任何想法为什么？

It happens also when v2 is Object[0] and also when there are Strings in it. Any Idea why?

推荐答案

这是因为当你使用

 toArray() 

它返回一个Object [ ]，无法强制转换为String []（即使内容是字符串）这是因为toArray方法只获得

it returns an Object[], which can't be cast to a String[] (even tho the contents are Strings) This is because the toArray method only gets a

List 

而不是

List<String>

因为泛型只是源代码，在运行时不可用，所以无法确定要创建什么类型的数组。

as generics are a source code only thing, and not available at runtime and so it can't determine what type of array to create.

使用

toArray(new String[v2.size()]);

分配正确类型的数组（String []和正确大小）

which allocates the right kind of array (String[] and of the right size)

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