void remove()       

    Removes from the underlying collection the last element returned by the

 iterator (optional operation).  This method can be called only once per

 call to next.  The behavior of an iterator is unspecified if

 the underlying collection is modified while the iteration is in

 progress in any way other than by calling this method.

Iterator it=hs.keySet().iterator();      

通过迭代器删除：
        while(it.hasNext())

        {

            String str=(String)it.next();               

            System.out.println(hs);               

            it.remove();  

        }