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Re: Problem with generics and dynamic array copy

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Am 22.07.2011 21:27, schrieb Robert Klemme:
> On 22.07.2011 20:36, Sebastian wrote:
>> Am 22.07.2011 20:23, schrieb markspace:
>>> On 7/22/2011 10:30 AM, Sebastian wrote:
>>>
>>>>> public static final <T> T[] arraycopy( T[] src )
>>>>> {
>>>>> Class<T> componentType = src.getClass().getComponentType(); // !!!!
>>>
>>>
>>> RTFM. getComponentType() returns Class<?>, not Class<T>.
>>>
>>> <http://download.oracle.com/javase/6/docs/api/java/lang/Class.html#getComponentType%28%29>
>>>
>>>
>>>
>>>
>>> public Class<?> getComponentType()
>>>
>>> Returns the Class representing the component type of an array. If this
>>> class does not represent an array class this method returns null.
>>>
>>
>> well, yes, but given that src.getClass() must give one the class object
>> for arrays with component type T, why is the compiler not smart enough
>> to infer that the unknown class parameter in the return value of
>> getComponentType() must be T? As a human I can see that, that's why I
>> can cast to Class<T>, but I don't believe that I'm smarter than javac...
>
> The compiler has no idea what the semantics of getComponentType() is. It
> could be implemented as
>
> public Class<?> getComponentType() { return Object.class; }
>
> and still be conformant to the declaration. Hence it cannot do any
> automatic inference based on the fact you know that the array is T[].
> Btw, you can actually pass B[] where B is a subclass of T.
>
> Since Array.newInstance() accepts Class<?> you should simply use that -
> that cast to T[] is needed anyway.
>
> Of course, even better you scrap your implementation and use
>
> http://download.oracle.com/javase/6/docs/api/java/util/Arrays.html#copyOf%28T[],%20int%29
>
>
> Cheers
>
> robert
>
Thanks. Java has a confusing variety of ways to copy an array:
  - the copyOf and copyOfRange methods in Arrays
  - System.arraycopy
  - clone and do a cast

I'll go with your recommendation.

-- Sebastian
	

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Problem with generics and dynamic array copy Sebastian <sebastian@undisclosed.invalid> - 2011-07-22 19:26 +0200
  Re: Problem with generics and dynamic array copy Sebastian <sebastian@undisclosed.invalid> - 2011-07-22 19:30 +0200
    Re: Problem with generics and dynamic array copy markspace <-@.> - 2011-07-22 11:23 -0700
      Re: Problem with generics and dynamic array copy Sebastian <sebastian@undisclosed.invalid> - 2011-07-22 20:36 +0200
        Re: Problem with generics and dynamic array copy Robert Klemme <shortcutter@googlemail.com> - 2011-07-22 21:27 +0200
          Re: Problem with generics and dynamic array copy lewbloch <lewbloch@gmail.com> - 2011-07-22 13:33 -0700
          Re: Problem with generics and dynamic array copy Sebastian <sebastian@undisclosed.invalid> - 2011-07-22 22:37 +0200
            Re: Problem with generics and dynamic array copy lewbloch <lewbloch@gmail.com> - 2011-07-22 15:49 -0700

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