Variable containg a class extending Enum and implementing an interface

Question

I'd like to do something like this:

private Class<? extends Enum<?> implements IMultiBlockEnum> typeEnum;

How would I do that? The "&" instead of "implements" doesn't work, but Eclipse doesn't give a proper explanation either.

Christopher Klinge

Answer 1

You can only use & when declaring an inferred parameter type, like this:

<T extends Enum & IMultiBlockEnum> void x(T a) {}

Wildcard types may not specify a type intersection as an upper bound.

If you start wondering why it is so, consider what would be the return type of typeEnum.newInstance(). It would have to be both Enum<?> and IMultiBlockEnum at the same time.

For the relevant JLS quote please refer to this answer.

P.S. Another thing that makes little sense in your example is that you end up using two independent wildcards, but obviously want it to be captured as the same type.