/**
* Copyright 2005 JBoss Inc
*
* Licensed 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.drools.reteoo;
import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* This is a simple linked linked implementation. Each node must implement </code>LinkedListNode<code> so that it references
* the node before and after it. This way a node can be removed without having to scan the list to find it. This class
* does not provide an Iterator implementation as its designed for efficiency and not genericity. There are a number of
* ways to iterate the list.
* <p>
* Simple iterator:
* <pre>
* for ( LinkedListNode node = list.getFirst(); node != null; node = node.getNext() ) {
* }
* </pre>
*
* Iterator that pops the first entry:
* <pre>
* for ( LinkedListNode node = list.removeFirst(); node != null; node = list.removeFirst() ) {
* }
* </pre>
*
*
* @author <a href="mailto:mark.proctor@jboss.com">Mark Proctor</a>
* @author <a href="mailto:bob@werken.com">Bob McWhirter</a>
*
*/
public class ObjectSinkNodeList
implements
Externalizable {
private static final long serialVersionUID = 510l;
private ObjectSinkNode firstNode;
private ObjectSinkNode lastNode;
private int size;
/**
* Construct an empty <code>LinkedList</code>
*/
public ObjectSinkNodeList() {
}
public void readExternal(ObjectInput in) throws IOException,
ClassNotFoundException {
firstNode = (ObjectSinkNode) in.readObject();
lastNode = (ObjectSinkNode) in.readObject();
size = in.readInt();
}
public void writeExternal(ObjectOutput out) throws IOException {
out.writeObject( firstNode );
out.writeObject( lastNode );
out.writeInt( size );
}
/**
* Add a <code>ObjectSinkNode</code> to the list. If the <code>LinkedList</code> is empty then the first and
* last nodes are set to the added node.
*
* @param node
* The <code>ObjectSinkNode</code> to be added
*/
public void add(final ObjectSinkNode node) {
if ( this.firstNode == null ) {
this.firstNode = node;
this.lastNode = node;
} else {
this.lastNode.setNextObjectSinkNode( node );
node.setPreviousObjectSinkNode( this.lastNode );
this.lastNode = node;
}
this.size++;
}
/**
* Removes a <code>ObjectSinkNode</code> from the list. This works by attach the previous reference to the child reference.
* When the node to be removed is the first node it calls <code>removeFirst()</code>. When the node to be removed is the last node
* it calls <code>removeLast()</code>.
*
* @param node
* The <code>ObjectSinkNode</code> to be removed.
*/
public void remove(final ObjectSinkNode node) {
if ( (this.firstNode != node) && (this.lastNode != node) ) {
node.getPreviousObjectSinkNode().setNextObjectSinkNode( node.getNextObjectSinkNode() );
node.getNextObjectSinkNode().setPreviousObjectSinkNode( node.getPreviousObjectSinkNode() );
this.size--;
node.setPreviousObjectSinkNode( null );
node.setNextObjectSinkNode( null );
} else {
if ( this.firstNode == node ) {
removeFirst();
} else {
removeLast();
}
}
}
/**
* Return the first node in the list
* @return
* The first <code>ObjectSinkNode</code>.
*/
public final ObjectSinkNode getFirst() {
return this.firstNode;
}
/**
* Return the last node in the list
* @return
* The last <code>ObjectSinkNode</code>.
*/
public final ObjectSinkNode getLast() {
return this.lastNode;
}
/**
* Remove the first node from the list. The next node then becomes the first node. If this is the last
* node then both first and last node references are set to null.
*
* @return
* The first <code>ObjectSinkNode</code>.
*/
public ObjectSinkNode removeFirst() {
if ( this.firstNode == null ) {
return null;
}
final ObjectSinkNode node = this.firstNode;
this.firstNode = node.getNextObjectSinkNode();
node.setNextObjectSinkNode( null );
if ( this.firstNode != null ) {
this.firstNode.setPreviousObjectSinkNode( null );
} else {
this.lastNode = null;
}
this.size--;
return node;
}
/**
* Remove the last node from the list. The previous node then becomes the last node. If this is the last
* node then both first and last node references are set to null.
*
* @return
* The first <code>ObjectSinkNode</code>.
*/
public ObjectSinkNode removeLast() {
if ( this.lastNode == null ) {
return null;
}
final ObjectSinkNode node = this.lastNode;
this.lastNode = node.getPreviousObjectSinkNode();
node.setPreviousObjectSinkNode( null );
if ( this.lastNode != null ) {
this.lastNode.setNextObjectSinkNode( null );
} else {
this.firstNode = this.lastNode;
}
this.size--;
return node;
}
/**
* @return
* boolean value indicating the empty status of the list
*/
public final boolean isEmpty() {
return (this.firstNode == null);
}
/**
* Iterates the list removing all the nodes until there are no more nodes to remove.
*/
public void clear() {
while ( removeFirst() != null ) {
}
}
/**
* @return
* return size of the list as an int
*/
public final int size() {
return this.size;
}
/**
* Returns a list iterator
* @return
*/
public Iterator iterator() {
return new Iterator() {
private ObjectSinkNode currentNode = null;
private ObjectSinkNode nextNode = getFirst();
public boolean hasNext() {
return (this.nextNode != null);
}
public Object next() {
this.currentNode = this.nextNode;
if ( this.currentNode != null ) {
this.nextNode = this.currentNode.getNextObjectSinkNode();
} else {
throw new NoSuchElementException( "No more elements to return" );
}
return this.currentNode;
}
public void remove() {
if ( this.currentNode != null ) {
ObjectSinkNodeList.this.remove( this.currentNode );
this.currentNode = null;
} else {
throw new IllegalStateException( "No item to remove. Call next() before calling remove()." );
}
}
};
}
}