Request for review : 7121314 : Behavior mismatch between AbstractCollection.toArray(T[] ) and its spec

[David Holmes]

On 14/03/2012 2:49 PM, Eamonn McManus wrote:
>>>> Why don't we have
>>>> public<T super E>  T[] toArray(T[] a) ?
>>>> This would prevent from the cast
>>>> r[i] = (T)it.next();
>>>
>>> It's too late to change the method signature now.
>>
>> Sorry about my english, I meant why don't we have had ...
>> In other words, has there been a reason that it was not like that from the
>> beginning?
>
> Perhaps because it is not legal Java?

Thanks Eamonn!

That's ironic. :) In "The Java Programming Language" 3rd edition, 
Section 11.3 Generic Methods and Constructors, I use toArray as an 
example of a generic method. I then pose the question "Shouldn't there 
be some restriction between T and E as they must be compatible?", the 
answer to which is "logically there could be" but "there is no way to 
express this restriction. Only wildcards can be given a lower type 
bound". I then continue to point out that such a restriction is not 
strictly necessary as you might have a List<Object>, for example, that 
you only stored Strings into, so why shouldn't you be able to pass in a 
String[] to toArray? The runtime array-store checks will catch any 
unsuitable array.

Cheers,
David

> Éamonn
>
>
> On 13 March 2012 12:16, Ulf Zibis<Ulf.Zibis at gmx.de>  wrote:
>>
>> Am 10.03.2012 13:52, schrieb David Holmes:
>>>
>>> On 10/03/2012 12:02 PM, Ulf Zibis wrote:
>>>>
>>>> Why don't we have
>>>> public<T super E>  T[] toArray(T[] a) ?
>>>> This would prevent from the cast
>>>> r[i] = (T)it.next();
>>>
>>>
>>> It's too late to change the method signature now.
>>
>> Sorry about my english, I meant why don't we have had ...
>> In other words, has there been a reason that it was not like that from the
>> beginning?
>>
>>
>>> Wouldn't following statement potentially throw a ClassCastException ?
>>>>
>>>> r[i] = (T)it.next();
>>>
>>>
>>> Apparently not. I passed in a String[] when it should be Object[] and got
>>> ArrayStoreException. Checking the bytecode I don't see a checkcast.
>>
>> Thanks, checking that out.
>>
>> -Ulf
>>