public class DList<E> {

	//declares our variables
	DListNode<E> head;
	DListNode<E> tail;
	private int length;

	public DList()
	{
		this.length = 0;  //initializes length to zero.
		this.head = null; //initializes head to null.
		this.tail = null; //initializes tail to null.
	}

	public void addAtHead(E element) //method which adds an element to the Head node.
	{
	DListNode<E> node = new DListNode<E>(element, null, null);
	this.addAtHead(node);  //creates a new node at the head.

	}

	public void addAtTail(E element)  //method which adds an element to the tail node
	{
	DListNode<E> node = new DListNode<E>(element, null, null);
	this.addAtTail(node);  //creates a new node at the tail

	}

	public void addAtHead(DListNode<E> node)  //method which adds a new node at the head
	{

		if(head == null){   // if the value of head is null, sets the head and tail equal to node
			head = node;
			tail = node;
		}
		else if(head != null) {
			head.setPredecessor(node);   // if head isn't null sets the new node as the head nodes predecessor.
			node.setSuccessor(head);     //sets the new node as the current heads successor.
			head = node;				 //sets the new node equal to the head since it becomes the new head.
		}
		this.length++;  				 //increments the size of the list.

	}

	public void addAtTail(DListNode<E> node)  //method which adds a new node at the tail
	{


		if(tail == null){    // if the value of tail is null, sets the head and tail equal to new node
			head = node;
			tail = node;
		}
		else if(tail != null){

			tail.setSuccessor(node);   //if the tail isn't null, sets the new node as the current tails successor.
			node.setPredecessor(head);  //sets the new node as the current heads predecessor
			tail = node;                 // sets the tail equal to the new node
		}
		this.length++;  // increments the length
	}

	public void removeFromHead()  //method which removes node from head.
	{

		if (length == 1) {   //if the length is 1, the tail and head are both null.
			head = null;
			tail = null;
		}
		else if(length >1)
		{
			DListNode<E> remove = head.getSuccessor();  //declares a new variable remove set equal to the heads successor.
			remove.setPredecessor(null);                  //sets removes predecessor to null.
			head = remove;	//sets remove and head equal to each other.
		}

		length--;  //decrements the length


	}

	public void removeFromTail()
	{
		if(length == 1){    //if the length is 1, the tail and head are both null.
			head = null;
			tail = null;
		}
		else if(length > 1){
			DListNode<E> remove = tail.getPredecessor();    //declares a new variable remove set equal to the tails predecessor.
			remove.setSuccessor(null);						//sets the variable removes successor to null.
			tail = remove;									//sets tail and remove equal to another.

		}
		this.length--;  //decrements the length
	}

	public DListNode<E> getHead()  //method which returns the head
	{
		return this.head;

	}

	public void setHead(DListNode<E> head)   //method which sets the head to value head
	{
		this.head = head;
	}

	public int getLength()  //method which gets the length
	{
		return this.length;
	}

	public void setLength(int length) //method which sets the length to value length
	{

		this.length = length;
	}

	public DListNode<E> getTail() //method which gets the tail
	{
		return this.tail;
	}

	public void setTail(DListNode<E> tail)  //method which sets the tail to value tail.
	{
		this.tail = tail;
	}

}