Why does following code causing a compiler error:

"interfaces java.util.Collection and java.util.List are incompatible; both
define toArray(T[]), but with different return type"

public interface XList extends List, Collection {...}

same error with:
public interface XList<E> extends List<E>, Collection<E> {...}

and also when reimplementing the method:
public interface XList<E> extends List<E>, Collection<E>
{
    public <T> T[] toArray(T[] target);
}

but no error with:
public interface XList<E> extends List<E> {...}


The problem is, I need to inherit XList from an XCollection interface, so I
can't just inherit from java.util.List.