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From Marshall Schor <...@schor.com>
Subject Re: generics: getViewIterator
Date Sat, 08 Aug 2009 20:57:22 GMT
Jörn Kottmann wrote:
>
> On Aug 7, 2009, at 8:57 PM, Marshall Schor wrote:
>
>> getViewIterator in CASImpl is written with the signature:
>>  Iterator<CAS> getViewIterator()
>>
>> If you are working with things needing CASImpl objects, you would write:
>>
>>  Iterator<CAS> s = aCas.getViewIterator();
>>  while (s.hasNext()) {
>>    CASImpl ci = (CASImpl) s.next();
>>      ... code using ci...
>>  }
>>
>> If we changed the signature to:
>>  Iterator<T extends CAS> getViewIterator()
>> then you would write:
>>  Iterator<CASImpl> s = aCas.getViewIterator(); // cast done inside the
>> support code, not here
>>  while (s.hasNext()) {
>>    CASImpl ci = s.next();  // works OK without casting
>>      ... code using ci...
>>  }
>>
>> Would it be better to have that form of the signature?
>
> +1, though did not know that its possible, we should check other
> places too

+1 to checking other places :-) 

The tutorial on generics by Gilad Bracha, 
http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf,  on page 20 near
the top says:

> In general, if you have an API that only uses a type parameter T as an
> argument, its
> uses should take advantage of lower bounded wildcards (? super T).
> Conversely, if
> the API only returns T, you’ll give your clients more flexibility by
> using upper bounded
> wildcards (? extends T).

There are many cases I think in our generification where the 2nd part of
this, returning XXX<? extends T> or a variant, is a better choice.

-Marshall
>
>
> Jörn
>
>
>

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