@SuppressWarnings("unused")
public class DVListe
{
	///////////////////////////////////////////////////////////
	private class Node
	{
		Node	prev;
		Object	obj;
		Node	next;
		
		public Node(Node prev, Object obj, Node next)
		{
			this.prev = prev;
			this.obj  = obj;
			this.next = next;
		}
		
		public Node()
		{
			this(null, null, null);
		}
		
		public void setPrev(Node prev)     { this.prev = prev; }
		public Node getPrev()              { return this.prev; }
		public void setElement(Object obj) { this.obj = obj;   }
		public Object getElement()         { return this.obj;  }
		public void setNext(Node next)     { this.next = next; }
		public Node getNext()              { return this.next; }
	}
	///////////////////////////////////////////////////////////
	
	private Node head = null;
	private Node tail = null;
	
	public DVListe()
	{
		this.head = new Node();
		this.tail = new Node(this.head, null, null);
		this.head.setNext(this.tail);
	}
	
	public void addFirst(Object o)
	{
		Node n = new Node(this.head, o, this.head.getNext());
		n.getNext().setPrev(n);
		this.head.setNext(n);
	}
	
	public void addLast(Object o)
	{
		Node n = new Node(this.tail.getPrev(), o, this.tail);
		n.getPrev().setNext(n);
		this.tail.setPrev(n);
	}
	
	public Object getFirst()
	{
		return this.head.getNext().getElement();
	}
	
	public Object getLast()
	{
		return this.tail.getPrev().getElement();
	}
	
	public void removeFirst()
	{
		this.head.setNext(this.head.getNext().getNext());
		this.head.getNext().setPrev(this.head);
	}
	
	public void removeLast()
	{
		this.tail.setPrev(this.tail.getPrev().getPrev());
		this.tail.getPrev().setNext(this.tail);
	}
	
	public void removeElement(int i)
	{
		if (i < 0 ) { return; }
		if (i == 0) { this.removeFirst(); return; }
		
		Node l = this.head;
		
		int j = 0;
		for (; j < i; j++)
		{
			if (l.getNext().getNext() == this.tail) { break; }
			l = l.getNext();
		}
		
		if (j != i) { return; }
		else
		{
			l.setNext(l.getNext().getNext());
			l.getNext().setPrev(l);
		}
	}
	
	public void addElement(int i, Object o)
	{
		if (i < 0 ) { return; }
		if (i == 0) { this.addFirst(o); return; }
		
		Node l = this.head;
		
		int j = 0;
		for (; j < i; j++)
		{
			if (l.getNext() == this.tail) { break; }
			l = l.getNext();
		}
		
		if (j != i) { return; }
		else
		{
			Node n = new Node(l, o, l.getNext());
			n.getNext().setPrev(n);
			l.setNext(n);
		}
	}
	
	public String toString()
	{
		Node l = this.head;
		
		String s = "";
		while (l.getNext() != this.tail)
		{
			s += "[" + l.getNext().getElement().toString() + "] ";
			l  = l.getNext();
		}
		
		return s;
	}
	
	public static void main(String[] args)
	{
		DVListe L = new DVListe();
		L.addFirst("3");
		L.addFirst("2");
		L.addFirst("1");
		L.addLast ("4");
		L.addLast ("5");
		L.addLast ("6");
		L.addLast ("7");
		L.addLast ("8");
		L.addLast ("9");
		
		System.out.println("toString():\t\t" + L);
		
		System.out.println("getFirst():\t\t" + "[" + L.getFirst() + "]");
		
		System.out.println("getLast():\t\t" + "[" + L.getLast () + "]");
		
		L.removeFirst();
		System.out.println("removeFirst():\t\t" + L);
		
		L.removeLast();
		System.out.println("removeLast():\t\t" + L);
		
		L.removeElement(5);
		System.out.println("removeElement(5):\t" + L);
		
		L.removeElement(-1);
		System.out.println("removeElement(-1):\t" + L);
		
		L.removeElement(100);
		System.out.println("removeElement(100):\t" + L);
		
		L.addElement(5, "7");
		System.out.println("addElement(5, \"7\"):\t" + L);
		
		L.addElement(-1, null);
		System.out.println("addElement(-1, null):\t" + L);
		
		L.addElement(100, null);
		System.out.println("addElement(100, null):\t" + L);
	}
}