Generics - Legal alternative for (elements instanceof List<? extends Comparable>)

Question

I have this method which unique parameter (List elements) sets elements to a ListModel, but I need to make a validation to see if the generic type implements comparable and since such thing like:

if (elements instanceof List<? extends Comparable>)

is illegal, I don't know how to do the proper validation.

Update

I already have done this validation using:

(elements.size() > 0 && elements.get(0) instanceof Comparable)

but I want to know if is there a cleaner solution for that, using for example reflection?

Thanks in advance.

Answer 1

The generic type of a list is erased at runtime. For this to work you need to either require the parameter in the method signature or test each element individually.

public void doSomething(List<? extends Comparable> elements) {}

OR

for (Object o : elements) {
    if (o instanceof Comparable) {}
}

If you have control over the code, the former is preferred and cleaner; the later can be wrapped in a utility method call if needed.

Answer 2

That's not possible. instanceof is a runtime operator whereas generic information is lost at runtime (type-erasure).