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());
}
}
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