/** * $RCSfile$ * $Revision$ * $Date$ * * Copyright (C) 2004 Jive Software. All rights reserved. * * This software is published under the terms of the GNU Public License (GPL), * a copy of which is included in this distribution. */ 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. */ 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(); } }