org.apache.commons.collections.list.NodeCachingLinkedList Maven / Gradle / Ivy
Show all versions of commons-collections Show documentation
/* ====================================================================
* The Apache Software License, Version 1.1
*
* Copyright (c) 2001-2004 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowledgement:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowledgement may appear in the software itself,
* if and wherever such third-party acknowledgements normally appear.
*
* 4. The names "The Jakarta Project", "Commons", and "Apache Software
* Foundation" must not be used to endorse or promote products derived
* from this software without prior written permission. For written
* permission, please contact [email protected].
*
* 5. Products derived from this software may not be called "Apache"
* nor may "Apache" appear in their names without prior written
* permission of the Apache Software Foundation.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* List implementation that stores a cache of internal Node objects
* in an effort to reduce wasteful object creation.
*
* A linked list creates one Node for each item of data added. This can result in
* a lot of object creation and garbage collection. This implementation seeks to
* avoid that by maintaining a store of cached nodes.
*
* This implementation is suitable for long-lived lists where both add and remove
* are used. Short-lived lists, or lists which only grow will have worse performance
* using this class.
*
* Note that this implementation is not synchronized.
*
* @since Commons Collections 3.0
* @version $Revision: 1.5 $ $Date: 2004/01/14 21:43:17 $
*
* @author Jeff Varszegi
* @author Rich Dougherty
* @author Phil Steitz
* @author Stephen Colebourne
*/
public class NodeCachingLinkedList extends AbstractLinkedList implements Serializable {
/** Serialization version */
static final long serialVersionUID = 6897789178562232073L;
/**
* The default value for {@link #maximumCacheSize}.
*/
protected static final int DEFAULT_MAXIMUM_CACHE_SIZE = 20;
/**
* The first cached node, or null if no nodes are cached.
* Cached nodes are stored in a singly-linked list with
* next pointing to the next element.
*/
protected transient Node firstCachedNode;
/**
* The size of the cache.
*/
protected transient int cacheSize;
/**
* The maximum size of the cache.
*/
protected int maximumCacheSize;
//-----------------------------------------------------------------------
/**
* Constructor that creates.
*/
public NodeCachingLinkedList() {
this(DEFAULT_MAXIMUM_CACHE_SIZE);
}
/**
* Constructor that copies the specified collection
*
* @param coll the collection to copy
*/
public NodeCachingLinkedList(Collection coll) {
super(coll);
this.maximumCacheSize = DEFAULT_MAXIMUM_CACHE_SIZE;
}
/**
* Constructor that species the maximum cache size.
*
* @param maximumCacheSize the maximum cache size
*/
public NodeCachingLinkedList(int maximumCacheSize) {
super();
this.maximumCacheSize = maximumCacheSize;
init(); // must call init() as use super();
}
//-----------------------------------------------------------------------
/**
* Gets the maximum size of the cache.
*
* @return the maximum cache size
*/
protected int getMaximumCacheSize() {
return maximumCacheSize;
}
/**
* Sets the maximum size of the cache.
*
* @param maximumCacheSize the new maximum cache size
*/
protected void setMaximumCacheSize(int maximumCacheSize) {
this.maximumCacheSize = maximumCacheSize;
shrinkCacheToMaximumSize();
}
/**
* Reduce the size of the cache to the maximum, if necessary.
*/
protected void shrinkCacheToMaximumSize() {
// Rich Dougherty: This could be more efficient.
while (cacheSize > maximumCacheSize) {
getNodeFromCache();
}
}
/**
* Gets a node from the cache. If a node is returned, then the value of
* {@link #cacheSize} is decreased accordingly. The node that is returned
* will have null values for next, previous and element.
*
* @return a node, or null if there are no nodes in the cache.
*/
protected Node getNodeFromCache() {
if (cacheSize == 0) {
return null;
}
Node cachedNode = firstCachedNode;
firstCachedNode = cachedNode.next;
cachedNode.next = null; // This should be changed anyway, but defensively
// set it to null.
cacheSize--;
return cachedNode;
}
/**
* Checks whether the cache is full.
*
* @return true if the cache is full
*/
protected boolean isCacheFull() {
return cacheSize >= maximumCacheSize;
}
/**
* Adds a node to the cache, if the cache isn't full.
* The node's contents are cleared to so they can be garbage collected.
*
* @param node the node to add to the cache
*/
protected void addNodeToCache(Node node) {
if (isCacheFull()) {
// don't cache the node.
return;
}
// clear the node's contents and add it to the cache.
Node nextCachedNode = firstCachedNode;
node.previous = null;
node.next = nextCachedNode;
node.value = null;
firstCachedNode = node;
cacheSize++;
}
//-----------------------------------------------------------------------
/**
* Creates a new node, either by reusing one from the cache or creating
* a new one.
*
* @param value value of the new node
* @return the newly created node
*/
protected Node createNode(Object value) {
Node cachedNode = getNodeFromCache();
if (cachedNode == null) {
return super.createNode(value);
} else {
cachedNode.value = value;
return cachedNode;
}
}
/**
* Removes the node from the list, storing it in the cache for reuse
* if the cache is not yet full.
*
* @param node the node to remove
*/
protected void removeNode(Node node) {
super.removeNode(node);
addNodeToCache(node);
}
/**
* Removes all the nodes from the list, storing as many as required in the
* cache for reuse.
*
*/
protected void removeAllNodes() {
// Add the removed nodes to the cache, then remove the rest.
// We can add them to the cache before removing them, since
// {@link AbstractLinkedList.removeAllNodes()} removes the
// nodes by removing references directly from {@link #header}.
int numberOfNodesToCache = Math.min(size, maximumCacheSize - cacheSize);
Node node = header.next;
for (int currentIndex = 0; currentIndex < numberOfNodesToCache; currentIndex++) {
Node oldNode = node;
node = node.next;
addNodeToCache(oldNode);
}
super.removeAllNodes();
}
//-----------------------------------------------------------------------
/**
* Serializes the data held in this object to the stream specified.
*/
private void writeObject(ObjectOutputStream out) throws IOException {
out.defaultWriteObject();
doWriteObject(out);
}
/**
* Deserializes the data held in this object to the stream specified.
*/
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
in.defaultReadObject();
doReadObject(in);
}
}