Program Explanation Program: Filename: “DoublyLinkedList.java” //Define "DoublyLinkedList" class public class DoublyLinkedList<E> { //Declare required variables private ListNode<E> head; private ListNode<E> current; private ListNode<E> tail; //Default constructor for "DoublyLinkedList" class public DoublyLinkedList() { head = null; current = null; tail = null; } //Method definition of "length" public int length() { //Declare required variable int count_value = 0; ListNode<E> location = head; //Check condition while (location != null) { count_value++; location = location.getLink(); } //Return the result of count value return count_value; } //Method definition for "addANodeToStart" public void addANodeToStart(E add_data) { //Declare variable by using "ListNode" class ListNode<E> old_headNode = head; //Assign value to head head = new ListNode<E>(add_data, null, null); /* If tail is null, then */ if (tail == null) { /* Assign tail to head */ tail = head; } /* If old head is not null, then */ if (old_headNode != null) { /* Assign the below values */ head.link = old_headNode; old_headNode.previous = head; } //If current node is at old begin node if (current == head.link && current != null) { //Set previous node at current to head current.previous = head; } } //Method definition of "getDataAtCurrent()" public E getDataAtCurrent() { /* If current is not null, then */ if (current != null) //Returns the data at current return (current.data); //Otherwise else { //Display the below error message System.out.println("Getting data when current is not at any node."); System.exit(0); } //Returns null value return null; } //Method definition of "resetIteration()" public void resetIteration() { //Set current to head current = head; } //Method definition of "moreToIterate()" public boolean moreToIterate() { //Returns given result return (current != null); } //Method definition of "goToNext()" public void goToNext() { /* If current is not null, then */ if (current != null) { //Set current value to link value at current current = current.link; } /* If head is not null*/ else if (head != null) { //Display given message System.out.println("Iterated too many times or not initialized iteration."); System.exit(0); } //Otherwise else { //Display given error message System.out.println("Iterating with an empty list."); System.exit(0); } } //Method definition of "resetIterationReverse" public void resetIterationReverse() { current = tail; } //Method definition of "goToPrecious" public void goToPrevious() { /* If current is not null, then */ if (current != null) { //Set current to previous value at current current = current.previous; } /* If head is not null, then */ else if (head != null) { //Display given error statement System.out.println("Iterated too many times or not initialized iteration."); System.exit(0); } //Otherwise else { //Display given error statement System.out.println("Iterating with an empty list."); System.exit(0); } } //Method definition for insert node after current node public void insertNodeAfterCurrent(E new_data) { //Declare required variables ListNode<E> new_node = new ListNode<E>(); new_node.data = new_data; /* If tail is equal to current */ if (tail == current) { //Set tail to new node tail = new_node; } /* If current is not null, then */ if (current != null) { //Set below values new_node.link = current.link; current.link = new_node; new_node.previous = current; /* If the link value at new node is not null, then */ if (new_node.link != null) { //Set the value new_node.link.previous = new_node; } } /* If the value of head is not null, then */ else if (head != null) { System.out.println("Inserting when iterator is past all " + "nodes or not initialized iterator."); System.exit(0); } //Otherwise else { //Display below statement System.out.println("Using insert node after current with empty list."); System.exit(0); } } //Method definition of delete current node public void deleteCurrentNode() { //Declare variable using "ListNode" class ListNode<E> save_previous = null; /* If tail is equal to current and current is not null, then */ if (tail == current && current != null) { //Set tail to previous value at current node tail = current.previous; } /* If current and previous value at current node is not null, then */ if ((current != null) && (current.previous != null)) { //Set values for given variables save_previous = current.previous; current = current.link; save_previous.link = current; if (current != null) { current.previous = save_previous; } } /* If current is not null and previous value at current node is null, then */ else if ((current != null) && (current.previous == null)) { //Set below values for head node head = current.link; current = head; current.previous = null; } //Otherwise, that is current is equal to null, then else //current == null { System.out.println("Removing with not initialized current or an empty list."); System.exit(0); } } //Method definition for delete head node public void deleteHeadNode() { /* If tail is equalt to head, then */ if (tail == head) { //Set tail to null tail = null; } /* If head is not null, then */ if (head != null) { //Assign values for head head = head.getLink(); } //Otherwise, else { //Display below error message System.out.println("Removing from an empty list."); System.exit(0); } } //Method definition find in list public boolean findInList(E target_node) { //Declare required variables ListNode<E> location; location = head; E data_position; //Check condition while (location != null) { data_position = location.getData(); if (data_position.equals(target_node)) { current = location; return true; } location = location.getLink(); } //target_node was not found. current = null; return false; } //Method definition of "onList" public boolean onList(E target_node) { return (Find(target_node) != null); } //Method definition of "Find" private ListNode<E> Find(E target_node) { //Declare required variables ListNode<E> location; location = head; E data_position; //Check condition while (location != null) { data_position = location.getData(); if (data_position.equals(target_node)) return location; location = location.getLink(); } //Returns target_node was not found...