//StringLinkedList.java

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;
    }
}