262 lines
7.9 KiB
Java
262 lines
7.9 KiB
Java
/* SList.java */
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package com.SimpleDrawingApp.list;
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/**
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* A SList is a mutable singly-linked list ADT. Its implementation employs
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* a tail reference.
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*
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* DO NOT CHANGE THIS FILE.
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**/
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public class SList extends List {
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/**
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* (inherited) size is the number of items in the list.
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* head references the first node.
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* tail references the last node.
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**/
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protected SListNode head;
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protected SListNode tail;
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/* SList invariants:
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* 1) Either head == null and tail == null, or tail.next == null and the
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* SListNode referenced by tail can be reached from the head by a
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* sequence of zero or more "next" references. This implies that the
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* list is not circularly linked.
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* 2) The "size" field is the number of SListNodes that can be accessed
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* from head (including head itself) by a sequence of "next" references.
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* 3) For every SListNode x in an SList l, x.myList = l.
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**/
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/**
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* newNode() calls the SListNode constructor. Use this method to allocate
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* new SListNodes rather than calling the SListNode constructor directly.
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* That way, only this method need be overridden if a subclass of SList
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* wants to use a different kind of node.
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*
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* @param item the item to store in the node.
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* @param next the node following this node.
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**/
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protected SListNode newNode(Object item, SListNode next) {
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return new SListNode(item, this, next);
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}
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/**
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* SList() constructs for an empty SList.
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**/
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public SList() {
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head = null;
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tail = null;
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size = 0;
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}
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/**
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* insertFront() inserts an item at the front of this SList.
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*
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* @param item is the item to be inserted.
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*
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* Performance: runs in O(1) time.
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**/
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public void insertFront(Object item) {
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head = newNode(item, head);
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if (size == 0) {
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tail = head;
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}
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size++;
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}
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/**
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* insertBack() inserts an item at the back of this SList.
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*
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* @param item is the item to be inserted.
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*
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* Performance: runs in O(1) time.
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**/
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public void insertBack(Object item) {
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if (head == null) {
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head = newNode(item, null);
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tail = head;
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} else {
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tail.next = newNode(item, null);
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tail = tail.next;
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}
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size++;
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}
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/**
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* front() returns the node at the front of this SList. If the SList is
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* empty, return an "invalid" node--a node with the property that any
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* attempt to use it will cause an exception.
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*
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* @return a ListNode at the front of this SList.
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*
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* Performance: runs in O(1) time.
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*/
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public ListNode front() {
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if (head == null) {
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// Create an invalid node.
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SListNode node = newNode(null, null);
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node.myList = null;
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return node;
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} else {
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return head;
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}
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}
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/**
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* back() returns the node at the back of this SList. If the SList is
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* empty, return an "invalid" node--a node with the property that any
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* attempt to use it will cause an exception.
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*
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* @return a ListNode at the back of this SList.
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*
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* Performance: runs in O(1) time.
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*/
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public ListNode back() {
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if (tail == null) {
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// Create an invalid node.
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SListNode node = newNode(null, null);
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node.myList = null;
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return node;
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} else {
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return tail;
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}
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}
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/**
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* toString() returns a String representation of this SList.
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*
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* @return a String representation of this SList.
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*
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* Performance: runs in O(n) time, where n is the length of the list.
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*/
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public String toString() {
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String result = "[ ";
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SListNode current = head;
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while (current != null) {
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result = result + current.item + " ";
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current = current.next;
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}
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return result + "]";
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}
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private static void testInvalidNode(ListNode p) {
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System.out.println("p.isValidNode() should be false: " + p.isValidNode());
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try {
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p.item();
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System.out.println("p.item() should throw an exception, but didn't.");
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} catch (InvalidNodeException lbe) {
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System.out.println("p.item() should throw an exception, and did.");
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}
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try {
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p.setItem(new Integer(0));
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System.out.println("p.setItem() should throw an exception, but didn't.");
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} catch (InvalidNodeException lbe) {
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System.out.println("p.setItem() should throw an exception, and did.");
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}
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try {
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p.next();
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System.out.println("p.next() should throw an exception, but didn't.");
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} catch (InvalidNodeException lbe) {
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System.out.println("p.next() should throw an exception, and did.");
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}
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try {
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p.prev();
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System.out.println("p.prev() should throw an exception, but didn't.");
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} catch (InvalidNodeException lbe) {
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System.out.println("p.prev() should throw an exception, and did.");
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}
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try {
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p.insertBefore(new Integer(1));
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System.out.println("p.insertBefore() should throw an exception, but " +
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"didn't.");
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} catch (InvalidNodeException lbe) {
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System.out.println("p.insertBefore() should throw an exception, and did."
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);
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}
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try {
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p.insertAfter(new Integer(1));
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System.out.println("p.insertAfter() should throw an exception, but " +
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"didn't.");
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} catch (InvalidNodeException lbe) {
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System.out.println("p.insertAfter() should throw an exception, and did."
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);
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}
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try {
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p.remove();
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System.out.println("p.remove() should throw an exception, but didn't.");
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} catch (InvalidNodeException lbe) {
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System.out.println("p.remove() should throw an exception, and did.");
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}
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}
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private static void testEmpty() {
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List l = new SList();
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System.out.println("An empty list should be [ ]: " + l);
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System.out.println("l.isEmpty() should be true: " + l.isEmpty());
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System.out.println("l.length() should be 0: " + l.length());
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System.out.println("Finding front node p of l.");
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ListNode p = l.front();
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testInvalidNode(p);
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System.out.println("Finding back node p of l.");
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p = l.back();
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testInvalidNode(p);
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l.insertFront(new Integer(10));
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System.out.println("l after insertFront(10) should be [ 10 ]: " + l);
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}
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public static void main(String[] argv) {
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testEmpty();
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List l = new SList();
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l.insertFront(new Integer(3));
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l.insertFront(new Integer(2));
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l.insertFront(new Integer(1));
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System.out.println("l is a list of 3 elements: " + l);
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try {
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ListNode n;
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int i = 1;
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for (n = l.front(); n.isValidNode(); n = n.next()) {
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System.out.println("n.item() should be " + i + ": " + n.item());
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n.setItem(new Integer(((Integer) n.item()).intValue() * 2));
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System.out.println("n.item() should be " + 2 * i + ": " + n.item());
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i++;
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}
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System.out.println("After doubling all elements of l: " + l);
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testInvalidNode(n);
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i = 6;
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for (n = l.back(); n.isValidNode(); n = n.prev()) {
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System.out.println("n.item() should be " + i + ": " + n.item());
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n.setItem(new Integer(((Integer) n.item()).intValue() * 2));
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System.out.println("n.item() should be " + 2 * i + ": " + n.item());
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i = i - 2;
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}
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System.out.println("After doubling all elements of l again: " + l);
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testInvalidNode(n);
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n = l.front().next();
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System.out.println("Removing middle element (8) of l: " + n.item());
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n.remove();
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System.out.println("l is now: " + l);
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testInvalidNode(n);
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n = l.back();
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System.out.println("Removing end element (12) of l: " + n.item());
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n.remove();
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System.out.println("l is now: " + l);
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testInvalidNode(n);
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n = l.front();
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System.out.println("Removing first element (4) of l: " + n.item());
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n.remove();
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System.out.println("l is now: " + l);
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testInvalidNode(n);
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} catch (InvalidNodeException lbe) {
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System.err.println ("Caught InvalidNodeException that should not happen."
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);
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System.err.println ("Aborting the testing code.");
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}
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}
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}
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