class BinaryHeapQueue implements
        Queue,
        Externalizable {

    @Override
    public String toString() {
        return Stream.of( elements ).filter(Objects::nonNull).collect(toList() ).toString();
    }

    public  BinaryHeapQueue();
    public  BinaryHeapQueue(final Comparator<Activation> comparator);
    public  BinaryHeapQueue(final Comparator<Activation> comparator,
                           final int capacity);

}