A class for you to extend when you want object to maintain a doubly linked list
/** * 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. */ /** * 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 * @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; } } ///////////////////////////////////// /** * 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; import junit.framework.TestCase; /** * @author chirino */ public class LinkedNodeTest extends TestCase { static class IntLinkedNode extends LinkedNode { public final int v; public IntLinkedNode(int v) { this.v = v; }; @Override public String toString() { return "" + v; } } IntLinkedNode i1 = new IntLinkedNode(1); IntLinkedNode i2 = new IntLinkedNode(2); IntLinkedNode i3 = new IntLinkedNode(3); IntLinkedNode i4 = new IntLinkedNode(4); IntLinkedNode i5 = new IntLinkedNode(5); IntLinkedNode i6 = new IntLinkedNode(6); public void testLinkAfter() { i1.linkAfter(i2.linkAfter(i3)); // Order should be 1,2,3 assertTrue(i1.getNext() == i2); assertTrue(i1.getNext().getNext() == i3); assertNull(i1.getNext().getNext().getNext()); assertTrue(i3.getPrevious() == i2); assertTrue(i3.getPrevious().getPrevious() == i1); assertNull(i3.getPrevious().getPrevious().getPrevious()); assertTrue(i1.isHeadNode()); assertFalse(i1.isTailNode()); assertFalse(i2.isHeadNode()); assertFalse(i2.isTailNode()); assertTrue(i3.isTailNode()); assertFalse(i3.isHeadNode()); i1.linkAfter(i4.linkAfter(i5)); // Order should be 1,4,5,2,3 assertTrue(i1.getNext() == i4); assertTrue(i1.getNext().getNext() == i5); assertTrue(i1.getNext().getNext().getNext() == i2); assertTrue(i1.getNext().getNext().getNext().getNext() == i3); assertNull(i1.getNext().getNext().getNext().getNext().getNext()); assertTrue(i3.getPrevious() == i2); assertTrue(i3.getPrevious().getPrevious() == i5); assertTrue(i3.getPrevious().getPrevious().getPrevious() == i4); assertTrue(i3.getPrevious().getPrevious().getPrevious().getPrevious() == i1); assertNull(i3.getPrevious().getPrevious().getPrevious().getPrevious().getPrevious()); assertTrue(i1.isHeadNode()); assertFalse(i1.isTailNode()); assertFalse(i4.isHeadNode()); assertFalse(i4.isTailNode()); assertFalse(i5.isHeadNode()); assertFalse(i5.isTailNode()); assertFalse(i2.isHeadNode()); assertFalse(i2.isTailNode()); assertTrue(i3.isTailNode()); assertFalse(i3.isHeadNode()); } public void testLinkBefore() { i3.linkBefore(i2.linkBefore(i1)); assertTrue(i1.getNext() == i2); assertTrue(i1.getNext().getNext() == i3); assertNull(i1.getNext().getNext().getNext()); assertTrue(i3.getPrevious() == i2); assertTrue(i3.getPrevious().getPrevious() == i1); assertNull(i3.getPrevious().getPrevious().getPrevious()); assertTrue(i1.isHeadNode()); assertFalse(i1.isTailNode()); assertFalse(i2.isHeadNode()); assertFalse(i2.isTailNode()); assertTrue(i3.isTailNode()); assertFalse(i3.isHeadNode()); i2.linkBefore(i5.linkBefore(i4)); // Order should be 1,4,5,2,3 assertTrue(i1.getNext() == i4); assertTrue(i1.getNext().getNext() == i5); assertTrue(i1.getNext().getNext().getNext() == i2); assertTrue(i1.getNext().getNext().getNext().getNext() == i3); assertNull(i1.getNext().getNext().getNext().getNext().getNext()); assertTrue(i3.getPrevious() == i2); assertTrue(i3.getPrevious().getPrevious() == i5); assertTrue(i3.getPrevious().getPrevious().getPrevious() == i4); assertTrue(i3.getPrevious().getPrevious().getPrevious().getPrevious() == i1); assertNull(i3.getPrevious().getPrevious().getPrevious().getPrevious().getPrevious()); assertTrue(i1.isHeadNode()); assertFalse(i1.isTailNode()); assertFalse(i4.isHeadNode()); assertFalse(i4.isTailNode()); assertFalse(i5.isHeadNode()); assertFalse(i5.isTailNode()); assertFalse(i2.isHeadNode()); assertFalse(i2.isTailNode()); assertTrue(i3.isTailNode()); assertFalse(i3.isHeadNode()); } public void testUnlink() { i1.linkAfter(i2.linkAfter(i3)); i3.linkAfter(i4); i1.linkBefore(i5); i1.linkAfter(i6); // Order should be 5,1,6,2,3,4 i4.unlink(); i5.unlink(); i6.unlink(); // Order should be 1,2,3 assertTrue(i1.getNext() == i2); assertTrue(i1.getNext().getNext() == i3); assertNull(i1.getNext().getNext().getNext()); assertTrue(i3.getPrevious() == i2); assertTrue(i3.getPrevious().getPrevious() == i1); assertNull(i3.getPrevious().getPrevious().getPrevious()); assertTrue(i1.isHeadNode()); assertFalse(i1.isTailNode()); assertFalse(i2.isHeadNode()); assertFalse(i2.isTailNode()); assertTrue(i3.isTailNode()); assertFalse(i3.isHeadNode()); } }