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/**
* $RCSfile$
* $Revision$
* $Date$
*
* Copyright (C) 2004-2008 Jive Software. All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.jivesoftware.util;
/**
* Simple LinkedList implementation. The main feature is that list nodes
* are public, which allows very fast delete operations when one has a
* reference to the node that is to be deleted.<p>
*
* @author Jive Software
*/
public class LinkedList {
/**
* The root of the list keeps a reference to both the first and last
* elements of the list.
*/
private LinkedListNode head = new LinkedListNode("head", null, null);
/**
* Creates a new linked list.
*/
public LinkedList() {
head.next = head.previous = head;
}
/**
* Returns the first linked list node in the list.
*
* @return the first element of the list.
*/
public LinkedListNode getFirst() {
LinkedListNode node = head.next;
if (node == head) {
return null;
}
return node;
}
/**
* Returns the last linked list node in the list.
*
* @return the last element of the list.
*/
public LinkedListNode getLast() {
LinkedListNode node = head.previous;
if (node == head) {
return null;
}
return node;
}
/**
* Adds a node to the beginning of the list.
*
* @param node the node to add to the beginning of the list.
*/
public LinkedListNode addFirst(LinkedListNode node) {
node.next = head.next;
node.previous = head;
node.previous.next = node;
node.next.previous = node;
return node;
}
/**
* Adds an object to the beginning of the list by automatically creating a
* a new node and adding it to the beginning of the list.
*
* @param object the object to add to the beginning of the list.
* @return the node created to wrap the object.
*/
public LinkedListNode addFirst(Object object) {
LinkedListNode node = new LinkedListNode(object, head.next, head);
node.previous.next = node;
node.next.previous = node;
return node;
}
/**
* Adds an object to the end of the list by automatically creating a
* a new node and adding it to the end of the list.
*
* @param object the object to add to the end of the list.
* @return the node created to wrap the object.
*/
public LinkedListNode addLast(Object object) {
LinkedListNode node = new LinkedListNode(object, head, head.previous);
node.previous.next = node;
node.next.previous = node;
return node;
}
/**
* Erases all elements in the list and re-initializes it.
*/
public void clear() {
//Remove all references in the list.
LinkedListNode node = getLast();
while (node != null) {
node.remove();
node = getLast();
}
//Re-initialize.
head.next = head.previous = head;
}
/**
* Returns a String representation of the linked list with a comma
* delimited list of all the elements in the list.
*
* @return a String representation of the LinkedList.
*/
@Override
public String toString() {
LinkedListNode node = head.next;
StringBuilder buf = new StringBuilder();
while (node != head) {
buf.append(node.toString()).append(", ");
node = node.next;
}
return buf.toString();
}
}