Having this code:

import java.util.Collection;
import java.util.List;

abstract class TypeTest {

    interface I {}

    public Collection<? extends I> excludeFrom(Collection<? extends I> include, Collection<? extends I> exclude) {
        return copyOf(filter(include, not(in(exclude))));
    }

    interface Predicate<T> {
        boolean apply(T t);
    }

    abstract <T> Predicate<T> in(Collection<? extends T> target);
    abstract <T> Predicate<T> not(Predicate<T> aPredicate);
    abstract <E> List<E> copyOf(Iterable<? extends E> elements);

    abstract <T> Iterable<T> filter(Iterable<T> unfiltered, Predicate<? super T> predicate);
}

javac 8 produces a compiler error. But if excludeFrom is replaced with:

    public Collection<? extends I> filter(Collection<? extends I> include, Collection<? extends I> exclude) {
        Iterable<? extends I> myFiltered = filter(include, not(in(exclude)));
        return copyOf(myFiltered);
    }

it works.