Explicit Java Generation
Why T
can't generic be used as a return type class
if T extends Class
.
Example:
public class Foo<T extends Bar> {
Bar[] array = new Bar[200];
Optional<T> forIndex(int index) {
return Optional.ofNullable(array[index]);
}
}
T
extension required Bar
What does it mean T
should never have a casting problem, or am I accepting that? Can someone clarify.
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This is not the case with you. Everyone T
is Bar
, but not everyone Bar
is T
. T
more specialized than Bar
(every daughter is a dog, but not every dog is a dacha). This means it is return Optional.ofNullable(array[index]);
trying to match a Bar
to a T
, which is not possible.
What you can do is just the generic method:
public class Main {
Bar[] array = new Bar[200];
Optional<? super Bar> forIndex(int index) {
return Optional.ofNullable(array[index]);
}
}
You might want to look at this wiki page and googling PECS
might help too.
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