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Subject: Re: [configuration2]: AbstractConfiguration::getArray
To: Commons Users List <user@commons.apache.org>
References: <57211173.9000409@web.de> <57211476.3070200@oliver-heger.de>
 <nfscf6$k6j$1@ger.gmane.org>
 <EF1FFE9D-3F6E-4E20-AB77-00AA1D20D14F@honton.org>
 <nft74p$kgt$1@ger.gmane.org>
From: Oliver Heger <oliver.heger@oliver-heger.de>
Message-ID: <57226527.6020105@oliver-heger.de>
Date: Thu, 28 Apr 2016 21:31:51 +0200
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Hi Jörg,

Am 28.04.2016 um 16:34 schrieb Jörg Schaible:
> Chas Honton wrote:
> 
>> Try casting Object[] to long[]. The compiler and the runtime will
>> complain.
> 
> It is not about a cast, it's about returning the proper object. And it has 
> nothing to do with primitives, because you cannot cast e.g. Object[] to 
> String[] either.

my first idea was the generic version, too. However, as Chas said, it is
not possible to make a method with such a signature return an array of
primitives. After type erasure, you have

public Object[] toArray(Class cls, String key)

and a primitive array is not an Object[].

Oliver

> 
>>
>>> On Apr 27, 2016, at 11:59 PM, Jörg Schaible
>>> <joerg.schaible@bpm-inspire.com> wrote:
>>>
>>> Hi Oliver,
>>>
>>> Oliver Heger wrote:
>>>
>>>> Hi Rainer,
>>>>
>>>>> Am 27.04.2016 um 21:22 schrieb Rainer Hirschmiller:
>>>>> Hi.
>>>>>
>>>>> I wonder why AbstractConfiguration::getArray(cls, key) returns a single
>>>>> object, not an array of objects? Can somebody explain why the caller
>>>>> have to make an explicit cast?
>>>>>
>>>>> e.g.
>>>>> AbstractConfiguration &configuration = ....;
>>>>>
>>>>> Object obj = configuration.getArray(String.class, "key);
>>>>> // expected Object[] obj = configuration.getArray(String.class, "key);
>>>>
>>>> the explanation can be found in the Javadocs of the ConversionHandler
>>>> interface which is used behind the scenes. Citing from the docs of the
>>>> toArray() method:
>>>>
>>>> "Note that the result type of this method is Object; because this method
>>>> can also produce arrays of a primitive type the return type Object[]
>>>> cannot be used."
>>>
>>> That does not explain, why the method is not declared using generics:
>>>
>>>  public <T> T[] toArray(Class<T> cls, String key);
>>>
>>> Cheers,
>>> Jörg
>>>
>>>
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> 
> 
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