001 /** 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.activemq.util; 018 019 /** 020 * Provides a base class for you to extend when you want object to maintain a 021 * doubly linked list to other objects without using a collection class. 022 * 023 * @author chirino 024 */ 025 public class LinkedNode { 026 027 protected LinkedNode next = this; 028 protected LinkedNode prev = this; 029 protected boolean tail = true; 030 031 public LinkedNode getHeadNode() { 032 if (isHeadNode()) { 033 return this; 034 } 035 if (isTailNode()) { 036 return next; 037 } 038 LinkedNode rc = prev; 039 while (!rc.isHeadNode()) { 040 rc = rc.prev; 041 } 042 return rc; 043 } 044 045 public LinkedNode getTailNode() { 046 if (isTailNode()) { 047 return this; 048 } 049 if (isHeadNode()) { 050 return prev; 051 } 052 LinkedNode rc = next; 053 while (!rc.isTailNode()) { 054 rc = rc.next; 055 } 056 return rc; 057 } 058 059 public LinkedNode getNext() { 060 return tail ? null : next; 061 } 062 063 public LinkedNode getPrevious() { 064 return prev.tail ? null : prev; 065 } 066 067 public boolean isHeadNode() { 068 return prev.isTailNode(); 069 } 070 071 public boolean isTailNode() { 072 return tail; 073 } 074 075 /** 076 * @param rightHead the node to link after this node. 077 * @return this 078 */ 079 public LinkedNode linkAfter(LinkedNode rightHead) { 080 081 if (rightHead == this) { 082 throw new IllegalArgumentException("You cannot link to yourself"); 083 } 084 if (!rightHead.isHeadNode()) { 085 throw new IllegalArgumentException("You only insert nodes that are the first in a list"); 086 } 087 088 LinkedNode rightTail = rightHead.prev; 089 090 if (tail) { 091 tail = false; 092 } else { 093 rightTail.tail = false; 094 } 095 096 rightHead.prev = this; // link the head of the right side. 097 rightTail.next = next; // link the tail of the right side 098 next.prev = rightTail; // link the head of the left side 099 next = rightHead; // link the tail of the left side. 100 101 return this; 102 } 103 104 /** 105 * @param leftHead the node to link after this node. 106 * @return 107 * @return this 108 */ 109 public LinkedNode linkBefore(LinkedNode leftHead) { 110 111 if (leftHead == this) { 112 throw new IllegalArgumentException("You cannot link to yourself"); 113 } 114 if (!leftHead.isHeadNode()) { 115 throw new IllegalArgumentException("You only insert nodes that are the first in a list"); 116 } 117 118 // The left side is no longer going to be a tail.. 119 LinkedNode leftTail = leftHead.prev; 120 leftTail.tail = false; 121 122 leftTail.next = this; // link the tail of the left side. 123 leftHead.prev = prev; // link the head of the left side. 124 prev.next = leftHead; // link the tail of the right side. 125 prev = leftTail; // link the head of the right side. 126 127 return leftHead; 128 } 129 130 /** 131 * Removes this node out of the linked list it is chained in. 132 */ 133 public void unlink() { 134 // If we are allready unlinked... 135 if (prev == this) { 136 reset(); 137 return; 138 } 139 140 if (tail) { 141 prev.tail = true; 142 } 143 144 // Update the peers links.. 145 next.prev = prev; 146 prev.next = next; 147 148 // Update our links.. 149 reset(); 150 } 151 152 public void reset() { 153 next = this; 154 prev = this; 155 tail = true; 156 } 157 158 }