Java - How to pass in type Class<A<B>> to method

Question

I have one method, say getHystrixClass(Class<A<B>> clazz) . It requires input type of Class<A<B>> to pass in. How to do that? I have tried a few methods, but all of them failed at compilation time which are shown below with their corresponding error messages.

First trial

Put in class A

getHystrixClass(A.class)

ERROR MESSAGE : The method getHystrixClass(Class<A<B>>) in the type IHystrixProvider<A<B>> is not applicable for the arguments (Class<A>)

Second trial

Put in class B

getHystrixClass(B.class)

ERROR MESSAGE : The method getHystrixClass(Class<A<B>>) in the type IHystrixProvider<A<B>> is not applicable for the arguments (Class<B>)

Third trial

Put in class A<B>

getHystrixClass(A<B>.class)

ERROR MESSAGE : A cannot be resolved to a variable

Fourth trial

Create a dummy object and get class form it.

A<B> dummy = new A<B>();
getHystrixClass(dummy.getClass())

ERROR MESSAGE : The method getHystrixClass(Class<A<B>>) in the type IHystrixProvider<A<B>> is not applicable for the arguments (Class<capture#1-of ? extends A>)

Any hint? Sorry for my bad English.

---

Edit:

Hi, @GhostCat

The interface is look something like below

// Define by my team lead
public interface IHystrixProvider<T extends HystrixCommand, Rq> {
    T getHystrixClass(Class<T> hystrixCommand);
}

/**
* @param <R> the return type
*/
public abstract class HystrixCommand<R> extends ... {
    ...
}

Code of HystrixCommand.java is public repository which can get from GitHub

Answer 1

You can pass Class<A<B>> using a (unchecked) cast - this is necessary because there is no Class object that represents the generic type A<B> , only one for the raw type A .

getHystrixClass((Class<A<B>>) (Class) A.class)

This will perform casts in the following order:

Class<A> (type of A.class) -> Class -> Class<A<B>>

Note that you first need the cast to raw Class in order to avoid an incompatible cast warning. Both casts also have zero runtime overhead, because the raw type ( Class ) stays the same, only the type arguments change.