You might look at discussions so far as conceptually adding a
super-interface to Collection, but jamming all the methods
into Collection itself. It might be easier to pretend otherwise
for a while. If we had some really good names for these, we might
even prefer this way.
Here's sketch of Collection (Not yet for List and Map)
interface AnyCollection<E> {
boolean isEmpty();
boolean contains(E e); // not Object
boolean add(E e);
boolean remove(E e); // not Object
boolean removeIf(Predicate<? super E> filter);
void clear();
Iterator<E> iterator();
Stream<E> stream();
Stream<E> parallelStream();
boolean addAll(AnyCollection<? extends E> c);
boolean containsAll(AnyCollection<? extends E> c); // not Collection<?>
boolean removeAll(AnyCollection<? extends E> c); // not Collection<?>
boolean retainAll(AnyCollection<? extends E> c); // not Collection<?>
// to address other issues:
long elementCount(); // not size()
AnyCollection<E> adding(E e);
AnyCollection<E> removing(E e);
}
interface Collection<E> extends AnyCollection<E> {
int size();
boolean contains(Object o); // contravariant arg
boolean remove(Object o); // contravariant arg
Object[] toArray();
<T> T[] toArray(T[] a);
boolean equals(Object o); // declare for sake of Collection spec
int hashCode(); // declare for sake of Collection spec
boolean containsAll(Collection<?> c);
boolean removeAll(Collection<?> c);
boolean retainAll(Collection<?> c);
}
