Re: Cast to multidimensional arrays

From: BarryNL (barry_at_nospam.nl)
Date: 01/30/04 

Date: Fri, 30 Jan 2004 17:27:54 +0100

Jay wrote:
> Why does the following code produce a ClassCastException?
>
> ArrayList list = new ArrayList();
> list.add(new Object[]{"Test1", "..."});
> list.add(new Object[]{"Test2", "..."});
> list.add(new Object[]{"Test3", "..."});
>
> Object ar[][] = (Object[][]) list.toArray();
>
>
> The last line causes a ClassCastException... Yet, list.toArray() is
> just an array of objects which are themselves arrays of objects. So
> list.toArray is an Object[][], conceptually. Why does Java complain?

Because the toArray() method is returning an Object[] and the contents
of each array item just happens to be an Object[]. Consider that this
*is OK*, if used above:

         Object ar[] = list.toArray();
         ar[0] = "A String"; // No longer an Object[]

what you need to do is force the correct return type with:

         Object ar[][] = (Object[][]) list.toArray(new Object[0][]);

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