Lab Exercise 5 Queue LinkedList Class

/**
 * creating LinkedList that use private variables of Node
 * Single LinkedList
 *
 * @author MUHAMMAD AZRI BIN JASNI @ ABDUL RANI
 * @version 10 OCTOBER 2012
 */

public class LinkedList
{
    protected Node head;//head should always point to the first nod
    protected Node tail;
    protected Node current;
    private int counter=0;

    public LinkedList() {}

    public int size()
    {
        return counter;
    }

    public boolean isEmpty()
    {
        return (head==null);
        //return (size()==0);
    }

    public Node getFirst()
    {
        return head;
    }

    public Node getNext()
    {
        //return current.link;
        return current.getLink();
    }

    public void insertAtFront(Object data)
    {
        Node newNode = new Node(data);
        if (isEmpty())
        {
            //head = new Node();
            //tail = new Node();
            head = newNode;
            tail = newNode;
        }
        else
        {
           newNode.setLink(head); //link of newNode was set to be the same as address stored in head
           head = newNode; //head store the address of newNode
        }
        newNode = null;
        counter++;
    }

    public void insertAtBack(Object data)
    {
        Node newNode = new Node(data);
        if (isEmpty())
        {
            head = newNode;
            tail = newNode;
        }
        else
        {
            tail.setLink(newNode);
            tail = tail.getLink();
        }
        newNode = null;//remove reference at the end of operation
        counter++;
    }

    public void removeFromFront()
    {
        if (isEmpty())
        {
            System.err.println("List is Empty, can't remove element from front.");
        }
        else
        {
            current = head;
            head = head.getLink();
            current.setLink(null);
            counter--;
            current = null;//remove reference at the end of operation
        }
    }

    public void removeFromBack()
    {
        if (isEmpty())
        {
            System.err.println("List is Empty, can't remove element from back.");
        }
        else
        {
            current = head;

            while (current.getLink()!=tail)
            {
                current = current.getLink();
            }
            tail = current;
            current.setLink(null);
            counter--;
            current = null;//remove reference at the end of operation
        }
    }

    public void display()
    {
        //current = new Node();
        String output = "[";
        if (! isEmpty())
        {
            current = head;//take address so it point to first node
            while (current != null)
            {
                output += current.getData();
                if (current.getLink() != null)
                {
                    output += ", ";
                }
                current = getNext();//current = current.link;
            }
        }
        output += "]";
        System.out.println(output);
        current = null;//remove reference
    }
}