import java.util.Iterator;

public class CLList<Element>
{
   ListNode<Element> head;

   public CLList()
   {
      head = new ListNode<Element>(null, null);
      head.setNext(head);
   }

   public void addFirst(Element obj)
   {
      head.setNext(new ListNode<Element>(obj, head.getNext()));
   }

   public void addLast(Element obj)
   {
      ListNode<Element> current = head;
      while(current.getNext() != head)
         current = current.getNext();

      current.setNext(new ListNode<Element>(obj, head));
   }

   // postcondition: first object in list that equals obj has been removed
   //                returns true if an object is removed, returns false
   //                if no object in list equals obj
   public boolean remove(Element obj)
   {
      ListNode<Element> current = head;
      while(current.getNext() != head &&
            !current.getNext().getValue().equals(obj))
         current = current.getNext();
      if(current.getNext() == head)
      {
         return false;
      }
      else
      {
         current.setNext(current.getNext().getNext());
         return true;
      }
   }

   public String toString()
   {
      String result = "[";
      ListNode current = head.getNext();
      while(current != head)
      {
         result += current.getValue() + ", ";
         current = current.getNext();
      }
      result += "]";
      return result;
   }

   public Iterator<Element> iterator()
   {
      return new CLLIterator<Element>();
   }

  private class CLLIterator<Element> implements Iterator<Element>
  {
    private ListNode<Element> current;
    private ListNode<Element> prev;

    public CLLIterator()
    {
      current = (ListNode<Element>)head;
      prev = null;
    }

    public boolean hasNext()
    {
      return current.getNext() != head;
    }

    public Element next()
    {
      if(current.getNext() != head)
      {
        prev = current;
        current = current.getNext();
        return current.getValue();
      }
      else
        throw new IllegalStateException("next called with hasNext false");
    }

    public void remove()
    {
      if(prev != null)
      {
        prev.setNext(current.getNext());
        current = prev;
      }
      else
        throw new IllegalStateException("iterator remove with no call to next");
    }
  }
}