| /** |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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.apache.activemq.util; |
| |
| /** |
| * Provides a base class for you to extend when you want object to maintain a |
| * doubly linked list to other objects without using a collection class. |
| * |
| * @author chirino |
| */ |
| public class LinkedNode { |
| |
| protected LinkedNode next = this; |
| protected LinkedNode prev = this; |
| protected boolean tail = true; |
| |
| public LinkedNode getHeadNode() { |
| if (isHeadNode()) { |
| return this; |
| } |
| if (isTailNode()) { |
| return next; |
| } |
| LinkedNode rc = prev; |
| while (!rc.isHeadNode()) { |
| rc = rc.prev; |
| } |
| return rc; |
| } |
| |
| public LinkedNode getTailNode() { |
| if (isTailNode()) { |
| return this; |
| } |
| if (isHeadNode()) { |
| return prev; |
| } |
| LinkedNode rc = next; |
| while (!rc.isTailNode()) { |
| rc = rc.next; |
| } |
| return rc; |
| } |
| |
| public LinkedNode getNext() { |
| return tail ? null : next; |
| } |
| |
| public LinkedNode getPrevious() { |
| return prev.tail ? null : prev; |
| } |
| |
| public boolean isHeadNode() { |
| return prev.isTailNode(); |
| } |
| |
| public boolean isTailNode() { |
| return tail; |
| } |
| |
| /** |
| * @param rightHead the node to link after this node. |
| * @return this |
| */ |
| public LinkedNode linkAfter(LinkedNode rightHead) { |
| |
| if (rightHead == this) { |
| throw new IllegalArgumentException("You cannot link to yourself"); |
| } |
| if (!rightHead.isHeadNode()) { |
| throw new IllegalArgumentException("You only insert nodes that are the first in a list"); |
| } |
| |
| LinkedNode rightTail = rightHead.prev; |
| |
| if (tail) { |
| tail = false; |
| } else { |
| rightTail.tail = false; |
| } |
| |
| rightHead.prev = this; // link the head of the right side. |
| rightTail.next = next; // link the tail of the right side |
| next.prev = rightTail; // link the head of the left side |
| next = rightHead; // link the tail of the left side. |
| |
| return this; |
| } |
| |
| /** |
| * @param leftHead the node to link after this node. |
| * @return this |
| */ |
| public LinkedNode linkBefore(LinkedNode leftHead) { |
| |
| if (leftHead == this) { |
| throw new IllegalArgumentException("You cannot link to yourself"); |
| } |
| if (!leftHead.isHeadNode()) { |
| throw new IllegalArgumentException("You only insert nodes that are the first in a list"); |
| } |
| |
| // The left side is no longer going to be a tail.. |
| LinkedNode leftTail = leftHead.prev; |
| leftTail.tail = false; |
| |
| leftTail.next = this; // link the tail of the left side. |
| leftHead.prev = prev; // link the head of the left side. |
| prev.next = leftHead; // link the tail of the right side. |
| prev = leftTail; // link the head of the right side. |
| |
| return leftHead; |
| } |
| |
| /** |
| * Removes this node out of the linked list it is chained in. |
| */ |
| public void unlink() { |
| // If we are allready unlinked... |
| if (prev == this) { |
| reset(); |
| return; |
| } |
| |
| if (tail) { |
| prev.tail = true; |
| } |
| |
| // Update the peers links.. |
| next.prev = prev; |
| prev.next = next; |
| |
| // Update our links.. |
| reset(); |
| } |
| |
| public void reset() { |
| next = this; |
| prev = this; |
| tail = true; |
| } |
| } |