public class StringLinkedList
{
    private ListNode head;
    
    public StringLinkedList( )
    {
        head = null;
    }
    
    /**
     Displays the data on the list.
    */
    public void showList( )
    {
        ListNode position = head;
        while (position != null)
        {
            System.out.println(position.getData( ));
            position = position.getLink( );
        }
    }
    
    /**
     Returns the number of nodes on the list.
    */
    public int length( )
    {
        int count = 0;
        ListNode position = head;
        while (position != null)
        {
            count++;
            position = position.getLink( );
        }
        return count;
    }
    
    /**
     Adds a node containing the data addData at the 
     start of the list.
	*/
    public void addANodeToStart(String addData)
    {
        head = new ListNode(addData, head);
    }
    
    /**
     Deletes the first node on the list.
    */
    public void deleteHeadNode( )
    {
        if (head != null)
        {
            head = head.getLink( );
        }
        else
        {
            System.out.println("Deleting from an empty list.");
            System.exit(0);
        }
    }

    /**
     Sees whether target is on the list.
    */
    public boolean onList(String target)
    {
        return find(target) != null;
    }
    
    // Returns a reference to the first node containing the
    // target data. If target is not on the list, returns null.
	private ListNode find(String target)
    {
		boolean found = false;
        ListNode position = head;
        while ((position != null) && !found)
        {
            String dataAtPosition = position.getData( );
            if (dataAtPosition.equals(target))
				found = true;
			else
				position = position.getLink( );
        }

        return position;
    }
}