Does Java allow type parameters for type parameters?

Question

In Scala you can do such things:

trait A[T]

trait B[C[_] <: A[_]] {
    def apply[T](entity: C[T]): T
}

The Java analog would look something like this:

interface A<T>

interface B<C<?> extends A> {
   <T> T apply(entity: C<T>): T
}

You can use B with any type that extends A and use this sub-type's type parameter as an output type of the method.

But it doesn't compile, how would you do it in Java?

I'm trying to return from the function apply() the value of type T — Eddie Jamsession
– Eddie Jamsession, Commented Jul 26, 2014 at 12:29
Perhaps you could edit the question to explain in words what the Scala code does; currently, the question can only be answered by an expert in both languages. — IMSoP
– IMSoP, Commented Jul 26, 2014 at 12:36

drexin · Accepted Answer · 2014-07-26 12:57:13Z

6

No, you unfortunately can't do this. Java does not have higher kinded types.

answered Jul 26, 2014 at 12:57

drexin

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