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Question: java write a method to concatenate two doubly linked lists...

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Java. Write a method to concatenate two doubly linked lists L and M, with header and trailer sentinel nodes, into a single list L′. Write a main method to test the new method

public class DoublyLinkedList<E> {

private static class Node<E> {

private E element; // reference to the element stored at this node

private Node<E> prev; // reference to the previous node in the list

private Node<E> next; // reference to the subsequent node in the list

public Node(E e, Node<E> p, Node<E> n) {

element = e;

prev = p;

next = n;


// public accessor methods

public E getElement() { return element; }

public Node<E> getPrev() { return prev; }

public Node<E> getNext() { return next; }

// Update methods

public void setPrev(Node<E> p) { prev = p; }

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

} //----------- end of nested Node class -----------

// instance variables of the DoublyLinkedList

private Node<E> header; // header sentinel

private Node<E> trailer; // trailer sentinel

private int size = 0; // number of elements in the list

public DoublyLinkedList() {

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

trailer = new Node<>(null, header, null); // trailer is preceded by header

header.setNext(trailer); // header is followed by trailer


// public accessor methods

public int size() { return size; }

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

public E first() {

if (isEmpty()) return null;

return header.getNext().getElement(); // first element is beyond header


public E last() {

if (isEmpty()) return null;

return trailer.getPrev().getElement(); // last element is before trailer


// public update methods

public void addFirst(E e) {

addBetween(e, header, header.getNext()); // place just after the header


public void addLast(E e) {

addBetween(e, trailer.getPrev(), trailer); // place just before the trailer


public E removeFirst() {

if (isEmpty()) return null; // nothing to remove

return remove(header.getNext()); // first element is beyond header


public E removeLast() {

if (isEmpty()) return null; // nothing to remove

return remove(trailer.getPrev()); // last element is before trailer


// private update methods

private void addBetween(E e, Node<E> predecessor, Node<E> successor) {

// create and link a new node

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





private E remove(Node<E> node) {

Node<E> predecessor = node.getPrev();

Node<E> successor = node.getNext();




return node.getElement();



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