pure interface of interface java.util.Set<A>

public interface Set<A>
  implements Collection<A>
{
    public abstract int size();
    public abstract boolean isEmpty();
    public abstract boolean contains(A o);
    public abstract Iterator<A> iterator();
    public abstract Object[] toArray();
    public abstract boolean add(A o);
    public abstract boolean remove(A o);
    public abstract boolean containsAll(Collection<A> c);
    public abstract boolean addAll(Collection<A> c);
    public abstract boolean retainAll(Collection<A> c);
    public abstract boolean removeAll(Collection<A> c);
    public abstract void clear();
    public abstract boolean equals(Object o);
    public abstract int hashCode();
}