Lensovet: Lensovet moved page CS/61b/Homework/hw5/list/DList.java to Computer Science/61b/Homework/hw5/list/DList.java

2023-02-20T03:51:35Z

Lensovet moved page CS/61b/Homework/hw5/list/DList.java to Computer Science/61b/Homework/hw5/list/DList.java

Lensovet: moved CS 61b/Homework/hw5/list/DList.java to CS/61b/Homework/hw5/list/DList.java: fix cs 61b hierarchy

2010-11-14T06:00:19Z

moved CS 61b/Homework/hw5/list/DList.java to CS/61b/Homework/hw5/list/DList.java: fix cs 61b hierarchy

Lensovet at 07:08, 22 September 2007

2007-09-22T07:08:39Z

New page

{{code}}
/* DList.java */

package list;

/**
* A DList is a mutable doubly-linked list ADT. Its implementation is
* circularly-linked and employs a sentinel node at the head of the list.
*
* DO NOT CHANGE ANY METHOD PROTOTYPES IN THIS FILE.
**/

public class DList extends List {

/**
* (inherited) size is the number of items in the list.
* head references the sentinel node.
* Note that the sentinel node does not store an item, and is not included
* in the count stored by the "size" field.
*
* DO NOT CHANGE THE FOLLOWING FIELD DECLARATION.
**/

protected DListNode head;

/* DList invariants:
* 1) head != null.
* 2) For any DListNode x in a DList, x.next != null.
* 3) For any DListNode x in a DList, x.prev != null.
* 4) For any DListNode x in a DList, if x.next == y, then y.prev == x.
* 5) For any DListNode x in a DList, if x.prev == y, then y.next == x.
* 6) For any DList l, l.head.myList = null. (Note that l.head is the
* sentinel.)
* 7) For any DListNode x in a DList l EXCEPT l.head (the sentinel),
* x.myList = l.
* 8) size is the number of DListNodes, NOT COUNTING the sentinel,
* that can be accessed from the sentinel (head) by a sequence of
* "next" references.
**/

/**
* newNode() calls the DListNode constructor. Use this method to allocate
* new DListNodes rather than calling the DListNode constructor directly.
* That way, only this method need be overridden if a subclass of DList
* wants to use a different kind of node.
*
* @param item the item to store in the node.
* @param list the list that owns this node. (null for sentinels.)
* @param prev the node previous to this node.
* @param next the node following this node.
**/
protected DListNode newNode(Object item, DList list,
DListNode prev, DListNode next) {
return new DListNode(item, list, prev, next);
}

/**
* DList() constructs for an empty DList.
**/
public DList() {
size = 0;
head = newNode(null, null, null, null);
head.next = head;
head.prev = head;
}

/**
* insertFront() inserts an item at the front of this DList.
*
* @param item is the item to be inserted.
*
* Performance: runs in O(1) time.
**/
public void insertFront(Object item) {
DListNode node = newNode(item, this, head, head.next);
head.next.prev = node;
head.next = node;
size++;
}

/**
* insertBack() inserts an item at the back of this DList.
*
* @param item is the item to be inserted.
*
* Performance: runs in O(1) time.
**/
public void insertBack(Object item) {
DListNode node = newNode(item, this, head.prev, head);
head.prev.next = node;
head.prev = node;
size++;
}

/**
* front() returns the node at the front of this DList. If the DList is
* empty, return an "invalid" node--a node with the property that any
* attempt to use it will cause an exception. (The sentinel is "invalid".)
*
* DO NOT CHANGE THIS METHOD.
*
* @return a ListNode at the front of this DList.
*
* Performance: runs in O(1) time.
*/
public ListNode front() {
return head.next;
}

/**
* back() returns the node at the back of this DList. If the DList is
* empty, return an "invalid" node--a node with the property that any
* attempt to use it will cause an exception. (The sentinel is "invalid".)
*
* DO NOT CHANGE THIS METHOD.
*
* @return a ListNode at the back of this DList.
*
* Performance: runs in O(1) time.
*/
public ListNode back() {
return head.prev;
}

/**
* toString() returns a String representation of this DList.
*
* DO NOT CHANGE THIS METHOD.
*
* @return a String representation of this DList.
*
* Performance: runs in O(n) time, where n is the length of the list.
*/
public String toString() {
String result = "[ ";
DListNode current = head.next;
while (current != head) {
result = result + current.item + " ";
current = current.next;
}
return result + "]";
}

private static void testInvalidNode(ListNode p) {
System.out.println("p.isValidNode() should be false: " + p.isValidNode());
try {
p.item();
System.out.println("p.item() should throw an exception, but didn't.");
} catch (InvalidNodeException lbe) {
System.out.println("p.item() should throw an exception, and did.");
}
try {
p.setItem(new Integer(0));
System.out.println("p.setItem() should throw an exception, but didn't.");
} catch (InvalidNodeException lbe) {
System.out.println("p.setItem() should throw an exception, and did.");
}
try {
p.next();
System.out.println("p.next() should throw an exception, but didn't.");
} catch (InvalidNodeException lbe) {
System.out.println("p.next() should throw an exception, and did.");
}
try {
p.prev();
System.out.println("p.prev() should throw an exception, but didn't.");
} catch (InvalidNodeException lbe) {
System.out.println("p.prev() should throw an exception, and did.");
}
try {
p.insertBefore(new Integer(1));
System.out.println("p.insertBefore() should throw an exception, but " +
"didn't.");
} catch (InvalidNodeException lbe) {
System.out.println("p.insertBefore() should throw an exception, and did."
);
}
try {
p.insertAfter(new Integer(1));
System.out.println("p.insertAfter() should throw an exception, but " +
"didn't.");
} catch (InvalidNodeException lbe) {
System.out.println("p.insertAfter() should throw an exception, and did."
);
}
try {
p.remove();
System.out.println("p.remove() should throw an exception, but didn't.");
} catch (InvalidNodeException lbe) {
System.out.println("p.remove() should throw an exception, and did.");
}
}

private static void testEmpty() {
List l = new DList();
System.out.println("An empty list should be [ ]: " + l);
System.out.println("l.isEmpty() should be true: " + l.isEmpty());
System.out.println("l.length() should be 0: " + l.length());
System.out.println("Finding front node p of l.");
ListNode p = l.front();
testInvalidNode(p);
System.out.println("Finding back node p of l.");
p = l.back();
testInvalidNode(p);
l.insertFront(new Integer(10));
System.out.println("l after insertFront(10) should be [ 10 ]: " + l);
}

public static void main(String[] argv) {
testEmpty();
List l = new DList();
l.insertFront(new Integer(3));
l.insertFront(new Integer(2));
l.insertFront(new Integer(1));
System.out.println("l is a list of 3 elements: " + l);
try {
ListNode n;
int i = 1;
for (n = l.front(); n.isValidNode(); n = n.next()) {
System.out.println("n.item() should be " + i + ": " + n.item());
n.setItem(new Integer(((Integer) n.item()).intValue() * 2));
System.out.println("n.item() should be " + 2 * i + ": " + n.item());
i++;
}
System.out.println("After doubling all elements of l: " + l);
testInvalidNode(n);

i = 6;
for (n = l.back(); n.isValidNode(); n = n.prev()) {
System.out.println("n.item() should be " + i + ": " + n.item());
n.setItem(new Integer(((Integer) n.item()).intValue() * 2));
System.out.println("n.item() should be " + 2 * i + ": " + n.item());
i = i - 2;
}
System.out.println("After doubling all elements of l again: " + l);
testInvalidNode(n);

n = l.front().next();
System.out.println("Removing middle element (8) of l: " + n.item());
n.remove();
System.out.println("l is now: " + l);
testInvalidNode(n);
n = l.back();
System.out.println("Removing end element (12) of l: " + n.item());
n.remove();
System.out.println("l is now: " + l);
testInvalidNode(n);

n = l.front();
System.out.println("Removing first element (4) of l: " + n.item());
n.remove();
System.out.println("l is now: " + l);
testInvalidNode(n);
} catch (InvalidNodeException lbe) {
System.err.println ("Caught InvalidNodeException that should not happen."
);
System.err.println ("Aborting the testing code.");
}
}
}

← Older revision	Revision as of 03:51, 20 February 2023
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← Older revision	Revision as of 06:00, 14 November 2010
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Computer Science/61b/Homework/hw5/list/DList.java - Revision history

Lensovet: Lensovet moved page CS/61b/Homework/hw5/list/DList.java to Computer Science/61b/Homework/hw5/list/DList.java

Lensovet: moved CS 61b/Homework/hw5/list/DList.java to CS/61b/Homework/hw5/list/DList.java: fix cs 61b hierarchy

Lensovet at 07:08, 22 September 2007