1) To class DoublyLinkedList, add method reverse which reverse the order of the elements in the list. 2) Our implementation of a doubly list relies on two sentinel nodes, header and trailer. Reemployment

the DoublyLinkedList without using these nodes.

public class DoublyLinkedList {

private Node header;

private Nodetrailer;

private int size=0;

public DoublyLinkedList()

{

header=new Node<>(null,null,null);

trailer=new Node<>(null,header, null);

header.setNext(trailer);

}

public int size() { return size;}

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

public E first()

{

if (isEmpty()) return null;

return header.getNext().getElement();

}

public E last()

{

if (isEmpty()) return null;

return trailer.getPrev().getElement();

}

private void addBetween(E e, Node predecessor,Nodesuccessor)

{

Node newest=new Node<>(e,predecessor, successor);

predecessor.setNext(newest);

successor.setPrev(newest);

size++;

}

private E remove(Node e)

{

Node predecessor=e.getPrev();

Node successor=e.getNext();

predecessor.setNext(successor);

successor.setPrev(predecessor);

size--;

return e.getElement();

}

public void addFirst(E e)

{

addBetween(e,header,header.getNext());

}

public void addLast(E e)

{

addBetween(e,trailer.getPrev(),trailer);

}

public E removeFirst()

{

if(isEmpty()) return null;

return remove(header.getNext());

}

public E removeLast()

{

if(isEmpty()) return null;

return remove(trailer.getPrev());

}

private static class Node{

private E element;

private Node next;

private Node prev;

public Node(E e,Node p, Node n)

{

element=e;

prev=p;

next=n;

}

public E getElement(){ return element; }

public Node getPrev() { return prev;}

public Node getNext() { return next;}

public void setPrev(Node n) {prev=n;}

public void setNext(Node n) {next=n;}

}

}