public class DoublyLinkedList implements List {
	//Data
	private DNode head,tail;
	private int num;

	//Access methods
	public DNode getHead() { return head; }
	public void setHead(DNode p) { head = p; }
	public DNode getTail() { return tail; }
	public void setTail(DNode p) { tail = p; }
	public void setNum(int n) { num = n; }
	public int getNum() { return num; }

    //Constructor
	public DoublyLinkedList(){
		setHead(new DNode());
		setTail(new DNode());
		getTail().setLeft(head);
		getHead().setRight(tail);
		num = 0;
	}

	//Private methods
 	private DNode search(int index) throws IndexOutOfBoundsException {
 		if(index < 0 || index >= size()) throw new IndexOutOfBoundsException();
 		DNode p = getHead().getRight();
 		for(int i = 0; i < index; i++) p = p.getRight();
  		return p;
 	}

	//List methods
	public boolean add(Object element) { addLast(element) ; return true; }
	
	public void add(int index,Object obj) throws IndexOutOfBoundsException {
 		if(index == 0) addFirst(obj);
 		else if(index == size()) addLast(obj);
 		else {
  			DNode p = search(index);
  			DNode w = new DNode(obj);
  			w.setRight(p);
  			w.setLeft(p.getLeft());
  			p.getLeft().setRight(w);
  			p.setLeft(w);
  			num++;
 		}
	}
	
	public void addFirst(Object o){
		throw new UnsupportedOperationException();
	}
	
	public void addLast(Object o){
		throw new UnsupportedOperationException();
	}
	
	public boolean contains(Object arg) {
		throw new UnsupportedOperationException();
  	}
	
	public Object get(int index) { return search(index).getData(); }
	
	public Object getFirst() { return get(0); }
	
	public Object getLast() { return get(size()-1); }
	
	public int indexOf(Object element) {
		throw new UnsupportedOperationException();
	}
	
	public int lastIndexOf(Object element) {
		throw new UnsupportedOperationException();
	}
	
	public boolean isEmpty() { return num == 0; }
	
	public Iterator iterator() { 
		return new DoublyLinkedListIterator(this);
	}
	
	public Object remove(int index) throws IndexOutOfBoundsException {
 		if(index == 0) return removeFirst();
 		if(index == size()-1) return removeLast();
 		DNode p = search(index);
 		Object d = p.getData();
 		p.getRight().setLeft(p.getLeft());
 		p.getLeft().setRight(p.getRight());
 		num--;
 		return d;
 	}
	
	public Object remove(Object element) {
		throw new UnsupportedOperationException();
  	}
	
	public Object removeFirst(){
		throw new UnsupportedOperationException();
	}
	
	public Object removeLast(){
		throw new UnsupportedOperationException();
	}
	
	public Iterator reverseIterator() { 
		return new DoublyLinkedListReverseIterator(this);
	}
	
	public Object set(int index,Object obj) {
 		DNode p = search(index);
 		Object result = p.getData();
 		p.setData(obj);
 		return result;
	}
	
	public int size() { return num; }
	
	public String toString() {
		String result = "[";
		Iterator it = this.iterator();
		while(it.hasNext())
			result = result + it.next() + " ";
		return result + "]";
	}
}