Question

I have a method (that I can’t change, it belongs to a different project) defined in an interface that limits the input classes using generics to a Class that extends a Class (which in turn implements an interface), like this:

<P extends ParentInterface, E extends P> void register(Class<E> cl, Class<P> parent);

This works fine when you’re calling it normally, but in order to make it easier to register a potentially large number of classes this way (and unregister the same set when needed) I was hoping to store them in a Map<Class<? extends ParentInterface>, Class<? extends ParentInterface>> (or similar) and loop over it when registering/unregistering. Unfortunately this – predictably – leads to compile time errors saying bound mismatch:

Bound mismatch: The generic method register(Class<E>, Class<P>) is not applicable for the arguments (Class<capture#5-of ? extends ParentInterface, Class<capture#13-of ? extends ParentInterface>). The inferred type capture#5-of ? extends ParentInterface is not a valid substitute for the bounded parameter <E extends P>

Can I get around this in some way, or am I stuck doing individual calls and making sure I’m keeping the register and unregister calls synchronized?

Answer 1

does it help to make the class generic, that will EDIT not encapsulate but extends the Map interface?

public class TestMap <P extends ParentInterface, E extends P> extends HashMap implements Map {
    void registerall(){
        Class<E> key = (Class<E>) this.keySet().iterator().next();
        Class<P> val = (Class<P>) this.get(key);
        register(key, val);
    }

}