In the existing DoublyLinkedList class, write and test a non-static method named reverseList to reverse a doubly linked list. Write the testing code in the main method of the class DoublyLinkedList. For this purpose, you must only use and update the DoublyLinkedList.java file provided in Lesson2Examples posted in the eCentennial module “Lesson Examples (from textbook)” package Ex2; public class DoublyLinkedList { private static class Node { private E element; // reference to the element stored at this node private Node prev; // reference to the previous node in the list private Node next; // reference to the subsequent node in the list public Node(E e, Node p, Node n) { element = e; prev = p; next = n; } // public accessor methods public E getElement() { return element; } public Node getPrev() { return prev; } public Node getNext() { return next; } // Update methods public void setPrev(Node p) { prev = p; } public void setNext(Node n) { next = n; } } //----------- end of nested Node class ----------- // instance variables of the DoublyLinkedList private Node header; // header sentinel private Node 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 predecessor, Node successor) { // create and link a new node Node newest = new Node<>(e, predecessor, successor); predecessor.setNext(newest); successor.setPrev(newest); size++; } private E remove(Node node) { Node predecessor = node.getPrev(); Node successor = node.getNext(); predecessor.setNext(successor); successor.setPrev(predecessor); size--; return node.getElement(); } public String toString() { StringBuilder sb = new StringBuilder("("); Node walk = header.getNext(); while (walk != trailer) { sb.append(walk.getElement()); walk = walk.getNext(); if (walk != trailer) sb.append(", "); } sb.append(")"); return sb.toString(); } public void reverseLIst() { if } //main method public static void main(String[] args) { //create and populate a doubly linked list DoublyLinkedList list = new DoublyLinkedList(); list.addFirst("MSP"); list.addLast("ATL"); list.addLast("BOS"); // list.addFirst("LAX"); System.out.println(list); System.out.println(list.first()); // } } //----------- end of DoublyLinkedList class -----------
In the existing DoublyLinkedList class, write and test a non-static method named reverseList to reverse a doubly linked list. Write the testing code in the main method of the class DoublyLinkedList. For this purpose, you must only use and update the DoublyLinkedList.java file provided in Lesson2Examples posted in the eCentennial module “Lesson Examples (from textbook)”
package Ex2;
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);
predecessor.setNext(newest);
successor.setPrev(newest);
size++;
}
private E remove(Node<E> node) {
Node<E> predecessor = node.getPrev();
Node<E> successor = node.getNext();
predecessor.setNext(successor);
successor.setPrev(predecessor);
size--;
return node.getElement();
}
public String toString() {
StringBuilder sb = new StringBuilder("(");
Node<E> walk = header.getNext();
while (walk != trailer) {
sb.append(walk.getElement());
walk = walk.getNext();
if (walk != trailer)
sb.append(", ");
}
sb.append(")");
return sb.toString();
}
public void reverseLIst() {
if
}
//main method
public static void main(String[] args)
{
//create and populate a doubly linked list
DoublyLinkedList<String> list = new DoublyLinkedList<String>();
list.addFirst("MSP");
list.addLast("ATL");
list.addLast("BOS");
//
list.addFirst("LAX");
System.out.println(list);
System.out.println(list.first());
//
}
} //----------- end of DoublyLinkedList class -----------
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