Problem 3 (List Implementation) (35 points): Write a method in the DoublyLList class that deletes the first item containing a given value from a doubly linked list. The header of the method is as follows: public boolean removeValue(T aValue) where T is the general type of the objects in the list and the methods returns true if such an item is found and deleted. Include testing of the method in a main method of the DoublyLList class. ------------------------------------------------------------------------------------- /** A doubly-linked implementation of the ADT list. @author Frank M. Carrano @author Joseph Erickson @version 4.0 */ public class DoublyLList implements ListInterface { private Node firstNode; // Reference to first node private int numberOfEntries; public DoublyLList() { initializeDataFields(); } // end default constructor public final void clear() // Note the final method { initializeDataFields(); } // end clear public void add(T newEntry) // OutOfMemoryError possible { Node newNode = new Node(newEntry); if (isEmpty()) firstNode = newNode; else // Add to end of non-empty list { Node lastNode = getNodeAt(numberOfEntries); lastNode.setNextNode(newNode); // Make last node reference new node newNode.setPreviousNode(lastNode); } // end else numberOfEntries++; } // end add public void add(int newPosition, T newEntry) // OutOfMemoryError possible { if ((newPosition >= 1) && (newPosition <= numberOfEntries + 1)) { Node newNode = new Node(newEntry); if (newPosition == 1) // Case 1 { newNode.setNextNode(firstNode); if (firstNode != null) // List is not empty firstNode.setPreviousNode(newNode); firstNode = newNode; } // end if else // Case 2: List is not empty { // and newPosition > 1 Node nodeBefore = getNodeAt(newPosition - 1); Node nodeAfter = nodeBefore.getNextNode(); newNode.setNextNode(nodeAfter); newNode.setPreviousNode(nodeBefore); nodeBefore.setNextNode(newNode); if (nodeAfter != null) // not the last element nodeAfter.setPreviousNode(newNode); } // end else numberOfEntries++; } // end if else throw new IndexOutOfBoundsException("Illegal position given to add operation."); } // end add public T remove(int givenPosition) { T result = null; // Return value if ((givenPosition >= 1) && (givenPosition <= numberOfEntries)) { assert !isEmpty(); if (givenPosition == 1) // Case 1: Remove first entry { result = firstNode.getData(); // Save entry to be removed firstNode = firstNode.getNextNode(); firstNode.setPreviousNode(null); } // end if else // Case 2: Not first entry { /////////////////////////////////////////// // INSERT YOUR CODE HERE /////////////////////////////////////////// } // end else numberOfEntries--; return result; } // end if else throw new IndexOutOfBoundsException("Illegal position given to remove operation."); } // end remove public T replace(int givenPosition, T newEntry) { if ((givenPosition >= 1) && (givenPosition <= numberOfEntries)) { assert !isEmpty(); Node desiredNode = getNodeAt(givenPosition); T originalEntry = desiredNode.getData(); desiredNode.setData(newEntry); return originalEntry; } // end if else throw new IndexOutOfBoundsException("Illegal position given to replace operation."); } // end replace public T getEntry(int givenPosition) { if ((givenPosition >= 1) && (givenPosition <= numberOfEntries)) { assert !isEmpty(); return getNodeAt(givenPosition).getData(); } // end if else throw new IndexOutOfBoundsException("Illegal position given to getEntry operation."); } // end getEntry public boolean contains(T anEntry) { boolean found = false; Node currentNode = firstNode; while (!found && (currentNode != null)) { if (anEntry.equals(currentNode.getData())) found = true; else currentNode = currentNode.getNextNode(); } // end while return found; } // end contains public int getLength() { return numberOfEntries; } // end getLength public boolean isEmpty() { boolean result; if (numberOfEntries == 0) // Or getLength() == 0 { assert firstNode == null; result = true; } // end if else { assert firstNode != null; result = false; } // end else return result; } // end isEmpty public T[] toArray() { // The cast is safe because the new array contains null entries @SuppressWarnings("unchecked") T[] result = (T[])new Object[numberOfEntries]; // Unchecked cast int index = 0; Node currentNode = firstNode; while ((index < numberOfEntries) && (currentNode != null)) { result[index] = currentNode.getData(); currentNode = currentNode.getNextNode(); index++; } // end while return result; } // end toArray // Initializes the class's data fields to indicate an empty list. private void initializeDataFields() { firstNode = null; numberOfEntries = 0; } // end initializeDataFields // Returns a reference to the node at a given position. // Precondition: List is not empty; // 1 <= givenPosition <= numberOfEntries private Node getNodeAt(int givenPosition) { assert !isEmpty() && (1 <= givenPosition) && (givenPosition <= numberOfEntries); Node currentNode = firstNode; // Traverse the chain to locate the desired node // (skipped if givenPosition is 1) for (int counter = 1; counter < givenPosition; counter++) currentNode = currentNode.getNextNode(); assert currentNode != null; return currentNode; } // end getNodeAt private class Node { private T data; // Entry in list private Node next; // Link to next node private Node previous; // Link to previous node private Node(T dataPortion) { data = dataPortion; next = null; previous = null; } // end constructor private Node(T dataPortion, Node nextNode) { data = dataPortion; next = nextNode; previous = null; } // end constructor private T getData() { return data; } // end getData private void setData(T newData) { data = newData; } // end setData private Node getNextNode() { return next; } // end getNextNode private void setNextNode(Node nextNode) { next = nextNode; } // end setNextNode private Node getPreviousNode() { return previous; } // end getPreviousNode private void setPreviousNode(Node previousNode) { previous = previousNode; } // end setPreviousNode } // end Node } // end DoublyLList 

 ------------------------------------------------------------------------------------------- /** An interface for the ADT list. Entries in a list have positions that begin with 1. @author Frank M. Carrano @author Timothy M. Henry @version 4.0 */ public interface ListInterface { /** Adds a new entry to the end of this list. Entries currently in the list are unaffected. The list's size is increased by 1. @param newEntry The object to be added as a new entry. */ public void add(T newEntry); /** Adds a new entry at a specified position within this list. Entries originally at and above the specified position are at the next higher position within the list. The list's size is increased by 1. @param newPosition An integer that specifies the desired position of the new entry. @param newEntry The object to be added as a new entry. @throws IndexOutOfBoundsException if either newPosition < 1 or newPosition > getLength() + 1. */ public void add(int newPosition, T newEntry); /** Removes the entry at a given position from this list. Entries originally at positions higher than the given position are at the next lower position within the list, and the list's size is decreased by 1. @param givenPosition An integer that indicates the position of the entry to be removed. @return A reference to the removed entry. @throws IndexOutOfBoundsException if either givenPosition < 1 or givenPosition > getLength(). */ public T remove(int givenPosition); /** Removes all entries from this list. */ public void clear(); /** Replaces the entry at a given position in this list. @param givenPosition An integer that indicates the position of the entry to be replaced. @param newEntry The object that will replace the entry at the position givenPosition. @return The original entry that was replaced. @throws IndexOutOfBoundsException if either givenPosition < 1 or givenPosition > getLength(). */ public T replace(int givenPosition, T newEntry); /** Retrieves the entry at a given position in this list. @param givenPosition An integer that indicates the position of the desired entry. @return A reference to the indicated entry. @throws IndexOutOfBoundsException if either givenPosition < 1 or givenPosition > getLength(). */ public T getEntry(int givenPosition); /** Retrieves all entries that are in this list in the order in which they occur in the list. @return A newly allocated array of all the entries in the list. If the list is empty, the returned array is empty. */ public T[] toArray(); /** Sees whether this list contains a given entry. @param anEntry The object that is the desired entry. @return True if the list contains anEntry, or false if not. */ public boolean contains(T anEntry); /** Gets the length of this list. @return The integer number of entries currently in the list. */ public int getLength(); /** Sees whether this list is empty. @return True if the list is empty, or false if not. */ public boolean isEmpty(); } // end ListInterface