[kepler-dev] java question: array casts

[xiaowen]

Hi Tobin,

Perhaps you could try:

import java.util.List;
import java.util.LinkedList;

public class Test {
     public static void main(String arg[]) {
         List foo = new LinkedList();
         foo.add("This is a test");
         String bar[] = (String[])(foo.toArray(new String[foo.size()]));
         System.out.println(bar[0]);
     }
}

Xiaowen

On Aug 16, 2004, at 3:50 PM, Tobin Fricke wrote:

> I am building up a List of tokens that I eventually want to turn into 
> an
> ArrayToken.  I am using the intermediate List because I do not know the
> final array length a priori.
>
>  List resultList = new LinkedList();
>  Token t = ...
>  resultList.add(t);
>
> Now I want to turn this List of tokens into an ArrayToken.  The method
> resultList.toArray() will return an Object[] array containing exactly 
> the
> items in the list.  Now I want to call the ArrayToken(Token[])
> constructor.  I thought I might be able to cast Object[] to Token[] and
> Java might distribute the cast across the array:
>
>  return new ArrayToken((Token[])(resultList.toArray()));
>
> But that generates a ClassCastException (because it's true that the
> resultList.toArray() has type Object[] and not Token[], although it
> contains only Tokens).
>
> As a kludge, I can copy the contents of result into a new array of the
> proper type, although it's rather ridiculous to create a copy just to
> satisfy the typechecking:
>
>   Token[] resultArray = new Token[resultList.size()];
>   System.arraycopy(resultList.toArray(), 0, resultArray, 0,
>                    resultList.size());
>   return new ArrayToken(resultArray);
>
> Here's some stand-alone code to demonstrate the effect:
>
> import java.util.List;
> import java.util.LinkedList;
>
> public class ArrayCastExperiment {
>     public static void main(String arg[]) {
>         List foo = new LinkedList();
>         foo.add("This is a test");
>         String bar[] = (String[])(foo.toArray()); // CastCastException!
>         System.out.println(bar[0]);
>     }
> }
>
> What's the right way to do this?
>
> Tobin
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