// Implementation of lists, using doubly linked elements and keeping track of current element.
// (c) 1996 duane a. bailey, modified 2/28/98 by Kim Bruce, modified 10/3/99 Andrea Danyluk

import structure.*;

public class CurDoublyLinkedList extends DoublyLinkedList
{
    protected DoublyLinkedListElement current;	// special current elt
    protected boolean offRight,					// are we off list to right or left?
    				  offLeft;

    public CurDoublyLinkedList()
    // post: constructs an empty list
    {
    	super();
    	current = null;
    	offRight = true;
    	offLeft = true;
    }

	public void first()
	{
	// pre:  list is non-empty
	// post:  current set to first element of list
	}
	
	public void last()
	{
	// pre:  list is non-empty
	// post:  current set to last element of list
	}
	
	public void next()
	{
	// pre:  list is non-empty && not isOffRight()
	// post:  if is off left then make head the current elt, if current is tail then set
	//			current to null and make offRight true, else set current elt to be next 
	//			element of list.
	//		set offRight and offLeft appropriately in all cases
	}
	
	public void back()
	{
	// pre:  list is non-empty && not isOffLeft()
	// post:  if is off right then make tail the current elt, if current is head then set
	//			current to null and make offLeft true, else set current elt to be previous 
	//			element of list.
	//		set offRight and offLeft appropriately in all cases
	}
	
	public boolean isOffRight()
	{
	// pre:  list is non-empty
	// post:  return whether last move caused to fall off right end of list
	}
	
	public boolean isOffLeft()
	{
	// pre:  list is non-empty
	// post:  return whether last move caused to fall off left end of list
	}
	
	public Object getCurrent()
	{
	// pre:  List is not empty & !(isOffRight() || isOffLeft())
	// post:  Return value in current node.
	}
	
    public void addAfterCurrent(Object value)
    {
    // pre: value is not null, List non-empty & !(isOffRight() || isOffLeft())
    // post: adds element after current.  New elt is current.
    }

	public void deleteCurrent()
	{
	// pre:  list is non-empty  & !(isOffRight() || isOffLeft())
	// post:  Current element is deleted, successor is new current elt
	//			If deleted tail, then current is null and offRight is true
	}
			
    public void addToHead(Object value)
    // pre: value is not null
    // post: adds element to head of list and make it current
    {
	// construct a new element, making it the head
		super.addToHead(value);
		current = head;
		offRight = false;
		offLeft = false;
    }

    public Object removeFromHead()
    {
    // pre: list is not empty
    // post: removes first value from list, successor is current
    }

    public void addToTail(Object value)
    {
    // pre: value is not null
    // post: adds new value to tail of list and make it current
    }

    public Object removeFromTail()
    {
    // pre: list is not empty
    // post: removes value from tail of list, offRight is true
    //		and current is null
    }

    public boolean contains(Object value)
    {
    // pre: value not null
    // post: returns true iff value is in the list
    // 		sets current to first node containing value if there is one, 
    //		else set current to null and make offRight true
    }

    public void clear()
    {
    // post: removes all the elements from the list
    }
    
    public static void main(String[] args)
    {
   		System.out.println("Don't forget to do thorough testing...");

    }

}