How can I obtain the type parameter of a generic interface from an implementing class?

Question

I have this interface:

public interface EventHandler {
    void handle(T event);
}

And this class implementing it:

Answer 1

Resolve the type of T by the generic interface. E.g.

public interface SomeInterface {
}

public class SomeImplementation implements SomeInterface {

    public Class getGenericInterfaceType(){
        Class clazz = getClass();
        ParameterizedType parameterizedType = (ParameterizedType) clazz.getGenericInterfaces()[0];
        Type[] typeArguments = parameterizedType.getActualTypeArguments();
        Class typeArgument = (Class) typeArguments[0];
        return typeArgument;
    }
}

public static void main(String[] args) {
    SomeImplementation someImplementation = new SomeImplementation();
    System.out.println(someImplementation.getGenericInterfaceType());
}

PS: Keep in mind that the acutalTypeArguments are of type Type. They must not be a Class. In your case it is a Class because your type definition is EventHandler.