import java.util.NoSuchElementException;

public class LinkedList
{
	public LinkedList()
	{
		first = null;
		// last = null;	// see the LinkedList class "version B" methods below		
	}
	
	public Object getFirst()
	{
		if (first == null)
			throw new NoSuchElementException();
		return first.getValue();
	}
	
	public void addFirst(Object obj)
	{
		ListNode newNode = new ListNode(obj, first);
		first = newNode;
	}
	
	public Object removeFirst()
	{
		if (first == null)
			throw new NoSuchElementException();
		Object obj = first.getValue();
		first = first.getNext();
		return obj;
	}
	
	public Object getLast()
	{
		if (first == null)
			throw new NoSuchElementException();
		ListNode temp = first;
		while (temp.getNext() != null)
			temp = temp.getNext();
		return temp.getValue();
	}
	
	public void addLast(Object obj)
	{
		ListNode newNode = new ListNode(obj, null);
		ListNode temp = first;
		while (temp.getNext() != null)
			temp = temp.getNext();
		temp.setNext(newNode);
	}
	
	public Object removeLast()
	{
		if (first == null)
			throw new NoSuchElementException();
			
		if (first.getNext() == null)
		{
			Object obj = first.getValue();
			first = null;
			return obj;
		}
		ListNode temp = first;
		ListNode follower = temp;
		while (temp.getNext() != null)
		{
			follower = temp;
			temp = temp.getNext();
		}
		follower.setNext(null);
		return temp.getValue();
	}

	// The following "version B" methods would work if the last property 
	//	is included in the LinkedList class.
	
/*	
	public Object getLast()
	{
		if (first == null)
			throw new NoSuchElementException();
		return last.getValue();
	}
	
	public void addLast(Object obj)
	{
		ListNode newNode = new ListNode(obj, null);
		if (first == null)
		{
			first = newNode;
			last = newNode;
		}
		else
		{
			last.setNext(newNode);
			last = newNode;
		}
	}
	
	public Object removeLast()
	{
		if (first == null)
			throw new NoSuchElementException();
		ListNode temp = first;
		if (first.getNext() == null)
		{
			Object obj = first.getValue();
			first = null;
			last = null;
			return obj;
		}
		while (temp.getNext() != last)
		{
			temp = temp.getNext();
		}
		
		Object obj = last.getValue();
		temp.setNext(null);
		last = temp;
		return obj;
	}
*/	
	private ListNode first;
	// private ListNode last;	// see the  "version B" methods above			
}