Cast Supplier to Supplier java

Asked Apr 19 '20 at 16:53

Active Apr 19 '20 at 17:00

Viewed 29 times

I have an Interface IParent, an abstract class implementing it AbstractChild and a class extending the abstract class ConcreteChild. One other class Foo requires an instance of a Supplier<IParent>.

My problem is that I have an instance of a Supplier<ConceretChild> and I cannot cast it to the Supplier<IParent> I need or just pass it straight up.

The only thing I have tried is of course:

((Supplier<IParent>)childSupplier)

Compiler says cannot cast from Supplier<Child> to Supplier<Parent>.

edited Apr 19 '20 at 17:00

LeffeBrune

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asked Apr 19 '20 at 16:53

Kostas Thanasis

There is no difference between optional and supplier with respect to the generic type, hence the dupe - it's relevant, honest. – Andy Turner Apr 19 '20 at 17:01
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You cannot pass it directly because it's not a subtype. Generic types are not covariant. If A -> B, then Supplier !-> Supplier. – Prashant Pandey Apr 19 '20 at 17:03
Yes i didn't know how to search for it. Thank you. Should i delete this? @AndyTurner – Kostas Thanasis Apr 19 '20 at 17:05
@KostasThanasis up to you. It may be useful for people searching for Supplier. – Andy Turner Apr 19 '20 at 17:06
@PrashantPandey that is generally true, but in the case of Supplier, whose only method returns a T, it can also be used to return a (parent of T). – Andy Turner Apr 19 '20 at 17:08

Cast Supplier to Supplier java

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