Krzysztof Sobolewski 写道:
Spark Shen wrote:
Seems that in new version of JDK, EnumSet<E> and <capture of ? extends
E> (E was previously stated as <E extends Enum<E>>) are not considered
compatible.
After changing
EnumSet<E> set = (EnumSet<E>)collection;
into
EnumSet set = (EnumSet)collection;
, compilation using ant in command line succeeds.
...but gives "unsafe" warnings.
Would any one give a clue, why the are considered incompatible in this
version of JDK?
Maybe a bugfix? :)
As far as I understand generics, SomeClass<A> and SomeClass<B>, where B
extends A, *are* incompatible (per the spec). Generic types are not polymorphic.
The problematic line IMO should read:
EnumSet<? extends E> set = (EnumSet<? extends E>)collection;
Do you mean to change the problematic line into the above statement? I
have tried this already, but this type of cast will also give a
compilation error.
And I did not find a way to suppress the unchecked warning while
compilation succeed.
That's because collection seems to be an EnumSet of some unknown subclass of
E[1] and that connot be safely converted to EnumSet<E>.
[1] I guess this is in addAll() or its friends?
I guess 'its friends' refers to removeAll, containsAll, and retainAll.
:-) But all its friends have different signature as addAll
boolean addAll(*Collection<? extends E>* c)
boolean containsAll(*Collection<?>* c)
boolean removeAll(*Collection<?>* c)
boolean retainAll(*Collection<?>* c)
I guess you know why they are different.
So, in the implementation of all its friends, same problem is not
encountered.
-KS
--
Spark Shen
China Software Development Lab, IBM
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