Thread: need help with Doubly-Linked list programing in java

the code that i m working with is singly-link list and i have to implement it to the double-link list. I know all constructers will be sama but i got stock on implementation.. this is the code ...

public class LList<T>
	implements IList<T>
{
//	Define private inner class Node.
 
	private class Node
	{
		T data;
		Node next;
 
		Node(T data, Node next)
		{
			this.data = data;
			this.next = next;
		}
 
		Node(T data)
		{	this(data, null);	}
	}
 
//	Declare instance fields/variables.
 
	private Node head;
	private int count;
 
//	Define default constructor.
 
	public LList()
	{	this.clear();	}
 
//	Define private helper methods.
 
	/*
	 *	Precondition: 0 <= index < this.count.
	 */
	private Node getNodeAt(int index)
	{
		Node curr = this.head;
		for (int i = 0; i < index; i++)
			curr = curr.next;
		return curr;
	}
 
//	Define methods declared in interface IList<T>.
 
	@Override
	public int size()
	{	return this.count;	}
 
	@Override
	public void clear()
	{
		this.head = null;
		this.count = 0;
	}
 
	@Override
	public T get(int index)
	{
		T result = null;
		if (0 <= index && index < this.count)
			result = this.getNodeAt(index).data;
		return result;
	}
 
	@Override
	public T set(int index, T data)
	{
		T result = null;
		if (0 <= index && index < this.count) {
			Node curr = this.getNodeAt(index);
			result = curr.data;
			curr.data = data;
		}
		return result;
	}
 
	@Override
	public boolean add(T data)
	{
		Node newNode = new Node(data);
		if (this.count == 0)
			this.head = newNode;
		else {
			Node prev = this.getNodeAt(this.count - 1);
			prev.next = newNode;
		}
		this.count++;
		return true;
	}
 
	@Override
	public boolean add(int index, T data)
	{
		boolean result = false;
		if (0 <= index && index <= this.count) {
			if (index == 0) {
				Node newNode = new Node(data, this.head);
				this.head = newNode;
			}
			else {
				Node prev = this.getNodeAt(index - 1);
				Node next = prev.next;
				Node newNode = new Node(data, next);
				prev.next = newNode;
			}
			this.count++;
			result = true;
		}
		return result;
	}
 
	@Override
	public T remove(int index)
	{
		T result = null;
		if (0 <= index && index < this.count) {
			Node curr = null;
			if (index == 0) {
				curr = this.head;
				this.head = curr.next;
			}
			else {
				Node prev = this.getNodeAt(index - 1);
				curr = prev.next;
				prev.next = curr.next;
			}
			this.count--;
			result = curr.data;
		}
		return result;
	}
 
	@Override
	public int indexOf(T that)
	{
		int result = -1;
		Node curr = this.head;
		for (int i = 0; result == -1 && i < this.count; i++) {
			if (that.equals(curr.data)) result = i;
			curr = curr.next;
		}
		return result;
	}
 
	@Override
	public boolean contains(T that)
	{
		return this.indexOf(that) >= 0;
	}
 
//	Override methods defined in Object.
 
	@Override
	public String toString()
	{
		StringBuilder sb = new StringBuilder("[");
		Node curr = this.head;
		for (int i = 0; i < this.count; i++) {
			if (i > 0) sb.append(", ");
			sb.append(curr.data);
			curr = curr.next;
		}
		sb.append(']');
		return sb.toString();
	}
 
	@Override
	@SuppressWarnings("unchecked")
	public boolean equals(Object other)
	{
		boolean result = false;
		if (other != null) {
			if (this.getClass() == other.getClass()) {
				LList<T> that = (LList<T>)other;
				if (this.size() == that.size()) {
					Node thisCurr = this.head;
					Node thatCurr = that.head;
					for (int i = 0; i < this.count; i++) {
						if ( ! thisCurr.data.equals(thatCurr.data)) break;
						thisCurr = thisCurr.next;
						thatCurr = thatCurr.next;
					}
					if (thisCurr == null) result = true;
				}
			}
		}
		return result;
	}
 
//	Define main() method to unit test this class.
 
	public static void main(String[] args)
	{
		IList<String> list = new LList<String>();
		String s;
		int i;
 
		System.out.printf("%d: %s%n", list.size(), list);
		list.add("Hello");
		System.out.printf("%d: %s%n", list.size(), list);
		list.add("World");
		System.out.printf("%d: %s%n", list.size(), list);
		list.add(0, "Well");
		System.out.printf("%d: %s%n", list.size(), list);
		list.add(2, "New");
		System.out.printf("%d: %s%n", list.size(), list);
		list.add(list.size(), ".");
		System.out.printf("%d: %s%n", list.size(), list);
		s = list.get(2);
		System.out.printf("retrieved at %d: %s%n", 2, s);
		s = list.set(2, "new");
		System.out.printf("replaced at %d: %s%n", 2, s);
		System.out.printf("%d: %s%n", list.size(), list);
		s = list.get(5);
		System.out.printf("retrieved at %d: %s%n", 5, s);
 
		i = list.indexOf("new");
		System.out.printf("String /%s/ found at: %d%n", "new", i);
		i = list.indexOf("old");
		System.out.printf("String /%s/ found at: %d%n", "old", i);
 
		s = list.remove(0);
		System.out.printf("removed at %d: %s%n", 0, s);
		System.out.printf("%d: %s%n", list.size(), list);
		s = list.remove(list.size() - 1);
		System.out.printf("removed at %d: %s%n", list.size(), s);
		System.out.printf("%d: %s%n", list.size(), list);
		s = list.remove(0);
		System.out.printf("removed at %d: %s%n", 0, s);
		System.out.printf("%d: %s%n", list.size(), list);
		s = list.remove(0);
		System.out.printf("removed at %d: %s%n", 0, s);
		System.out.printf("%d: %s%n", list.size(), list);
		s = list.remove(0);
		System.out.printf("removed at %d: %s%n", 0, s);
		System.out.printf("%d: %s%n", list.size(), list);
 
		IList<String> la = new LList<String>();
		IList<String> lb = new LList<String>();
		for (char c = 'a'; c <= 'e'; c++) {
			s = String.format("%c", c);
			la.add(s);
			lb.add(s);
		}
		System.out.println();
		System.out.printf("%d: %s%n", la.size(), la);
		System.out.printf("%d: %s%n", lb.size(), lb);
		System.out.printf("la.equals(lb): %b%n", la.equals(lb));
		lb.set(3, "D");
		System.out.printf("%d: %s%n", lb.size(), lb);
		System.out.printf("la.equals(lb): %b%n", la.equals(lb));
	}
}

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