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Performance optimised LinkedList, from Jeff Varszegi 

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/collections/trunk@130866 13f79535-47bb-0310-9956-ffa450edef68
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Stephen Colebourne 2002-11-18 23:58:17 +00:00
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commit 4fbfa16c6e
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/*
* $Header: /home/jerenkrantz/tmp/commons/commons-convert/cvs/home/cvs/jakarta-commons//collections/src/java/org/apache/commons/collections/Attic/NodeCachingLinkedList.java,v 1.1 2002/11/18 23:58:17 scolebourne Exp $
* $Revision: 1.1 $
* $Date: 2002/11/18 23:58:17 $
*
* ====================================================================
*
* The Apache Software License, Version 1.1
*
* Copyright (c) 1999-2002 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 acknowlegement:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements 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 apache@apache.org.
*
* 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 Group.
*
* 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
* <http://www.apache.org/>.
*
*/
package org.apache.commons.collections;
import java.io.Serializable;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;
/**
* <code>NodeCachingLinkedList</code> is a linked list implementation that
* provides better performance than java.util.LinkedList.
* <p>
* This class differs from java.util.LinkedList in that internal Node
* objects used to hold the elements are not necessarily thrown away when an
* entry is removed from the list. Instead, they are cached, which allows this
* implementation to give better performance than java.util.LinkedList with a
* small space penalty.
* <p>
* <b>Note that this implementation is not synchronized.</b> If multiple
* threads access a list concurrently, and at least one of the threads
* modifies the list structurally, it <i>must</i> be synchronized
* externally.
* <p>
* The iterators returned by the this class's <code>iterator</code> and
* <code>listIterator</code> methods are <i>fail-fast</i>: if the list is
* structurally modified at any time after the iterator is created, in any way
* except through the Iterator's own <code>remove</code> or <code>add</code> methods,
* the iterator will throw a <code>ConcurrentModificationException</code>. Thus,
* in the face of concurrent modification, the iterator fails quickly and
* cleanly, rather than risking arbitrary, non-deterministic behavior at an
* undetermined time in the future.
* <p>
* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
* as it is, generally speaking, impossible to make any hard guarantees in the
* presence of unsynchronized concurrent modification. Fail-fast iterators
* throw <code>ConcurrentModificationException</code> on a best-effort basis.
* Therefore, it would be wrong to write a program that depended on this
* exception for its correctness: <i>the fail-fast behavior of iterators
* should be used only to detect bugs.</i>
*
* @author Jeff Varszegi
*/
public final class NodeCachingLinkedList
extends LinkedList
implements List, Cloneable, Serializable {
private static final int MINIMUM_MAXIMUM_CACHE_SIZE = 100;
private static final int DEFAULT_MAXIMUM_CACHE_SIZE = 1000000;
private Node cacheHeader = new Node(null, null, null);
private int cacheCount = 0;
private int maximumCacheSize = DEFAULT_MAXIMUM_CACHE_SIZE;
private Node header = new Node(null, null, null);
private int size = 0;
/**
* Constructs an empty list.
*/
public NodeCachingLinkedList() {
header.next = header.previous = header;
}
/**
* Constructs a list containing the elements of the specified
* collection, in the order they are returned by the collection's
* iterator.
*
* @param coll the collection whose elements are to be placed into this list.
* @throws NullPointerException if the specified collection is null.
*/
public NodeCachingLinkedList(Collection coll) {
this();
addAll(coll);
}
/**
* Sets the maximum number of elements that may be held in the internal
* reusable node cache.
*
* @return the maximum cache size
*/
public int getMaximumCacheSize() {
return maximumCacheSize;
}
/**
* Sets the maximum number of elements that may be held in the internal
* reusable node cache.
*
* @param maximumCacheSize the maximum cache size to set
*/
public void setMaximumCacheSize(int maximumCacheSize) {
this.maximumCacheSize = maximumCacheSize;
}
/**
* Returns the first element in this list.
*
* @return the first object in the list
* @throws NoSuchElementException if this list is empty
*/
public Object getFirst() {
if (size == 0) {
throw new NoSuchElementException();
}
else {
return header.next.element;
}
}
/**
* Returns the last element in this list.
*
* @return the last object in the list
* @throws NoSuchElementException if this list is empty
*/
public Object getLast() {
if (size == 0) {
throw new NoSuchElementException();
}
return header.previous.element;
}
/**
* Removes and returns the first element from this list.
*
* @return the first element from this list, now removed
* @throws NoSuchElementException if this list is empty
*/
public Object removeFirst() {
if (size == 0) {
throw new NoSuchElementException();
}
Node firstNode = header.next;
Object first = firstNode.element;
firstNode.next.previous = header;
header.next = firstNode.next;
size--;
modCount++;
if (cacheCount < maximumCacheSize) {
firstNode.element = null;
firstNode.next = cacheHeader.next;
cacheHeader.next = firstNode;
cacheCount++;
}
return first;
}
/**
* Removes and returns the last element from this list.
*
* @return the last element from this list, now removed
* @throws NoSuchElementException if this list is empty
*/
public Object removeLast() {
if (size == 0) {
throw new NoSuchElementException();
}
Node lastNode = header.previous;
Object last = lastNode.element;
lastNode.previous.next = header;
header.previous = lastNode.previous;
size--;
modCount++;
if (cacheCount < maximumCacheSize) {
lastNode.element = null;
lastNode.previous = null;
lastNode.next = cacheHeader.next;
cacheHeader.next = lastNode;
cacheCount++;
}
return last;
}
/**
* Inserts the given element at the beginning of this list.
*
* @param obj the element to be inserted at the beginning of this list
*/
public void addFirst(Object obj) {
Node newNode;
if (cacheCount > 0) {
newNode = cacheHeader.next;
cacheHeader.next = newNode.next;
newNode.element = obj;
newNode.next = header.next;
newNode.previous = header;
cacheCount--;
}
else {
newNode = new Node(obj, header.next, header);
}
newNode.previous.next = newNode;
newNode.next.previous = newNode;
size++;
modCount++;
}
/**
* Appends the given element to the end of this list. (Identical in
* function to the <code>add</code> method; included only for consistency.)
*
* @param obj the element to be inserted at the end of this list
*/
public void addLast(Object obj) {
Node newNode;
if (cacheCount > 0) {
newNode = cacheHeader.next;
cacheHeader.next = newNode.next;
newNode.element = obj;
newNode.next = header.next;
newNode.previous = header;
cacheCount--;
}
else {
newNode = new Node(obj, header, header.previous);
}
newNode.previous.next = newNode;
newNode.next.previous = newNode;
size++;
modCount++;
}
/**
* Returns <code>true</code> if this list contains the specified element.
* More formally, returns <code>true</code> if and only if this list contains
* at least one element <code>e</code> such that <code>(o==null ? e==null
* : o.equals(e))</code>.
*
* @param obj element whose presence in this list is to be tested
* @return <code>true</code> if this list contains the specified element
*/
public boolean contains(Object obj) {
return indexOf(obj) != -1;
}
/**
* Returns the number of elements in this list.
*
* @return the number of elements in this list
*/
public int size() {
return size;
}
/**
* Appends the specified element to the end of this list.
*
* @param obj element to be appended to this list.
* @return <code>true</code> (as per the general contract of
* <code>Collection.add</code>)
*/
public boolean add(Object obj) {
addLast(obj);
return true;
}
/**
* Removes the first occurrence of the specified element in this list. If
* the list does not contain the element, it is unchanged. More formally,
* removes the element with the lowest index <code>i</code> such that
* <code>(o==null ? get(i)==null : o.equals(get(i)))</code> (if such an
* element exists).
*
* @param obj element to be removed from this list, if present
* @return <code>true</code> if the list contained the specified element
*/
public boolean remove(Object obj) {
if (obj == null) {
for (Node e = header.next; e != header; e = e.next) {
if (e.element == null) {
remove(e);
return true;
}
}
}
else {
for (Node e = header.next; e != header; e = e.next) {
if (obj.equals(e.element)) {
remove(e);
return true;
}
}
}
return false;
}
/**
* Appends all of the elements in the specified collection to the end of
* this list, in the order that they are returned by the specified
* collection's iterator. The behavior of this operation is undefined if
* the specified collection is modified while the operation is in
* progress. (This implies that the behavior of this call is undefined if
* the specified Collection is this list, and this list is nonempty.)
*
* @param coll the elements to be inserted into this list
* @return <code>true</code> if this list changed as a result of the call
* @throws NullPointerException if the specified collection is null
*/
public boolean addAll(Collection coll) {
return addAll(size, coll);
}
/**
* Inserts all of the elements in the specified collection into this
* list, starting at the specified position. Shifts the element
* currently at that position (if any) and any subsequent elements to
* the right (increases their indices). The new elements will appear
* in the list in the order that they are returned by the
* specified collection's iterator.
*
* @param index index at which to insert first element
* from the specified collection
* @param coll elements to be inserted into this list
* @return <code>true</code> if this list changed as a result of the call
* @throws IndexOutOfBoundsException if the specified index is out of
* range (<code>index &lt; 0 || index &gt; size()</code>)
* @throws NullPointerException if the specified collection is null
*/
public boolean addAll(int index, Collection coll) {
int numNew = coll.size();
if (numNew == 0)
return false;
modCount++;
Node successor = (index == size ? header : entry(index));
Node predecessor = successor.previous;
Iterator it = coll.iterator();
for (int i = 0; i < numNew; i++) {
Node e;
if (cacheCount > 0) {
e = cacheHeader.next;
cacheHeader.next = e.next;
e.element = it.next();
e.next = successor;
e.previous = predecessor;
}
else {
e = new Node(it.next(), successor, predecessor);
}
predecessor.next = e;
predecessor = e;
}
successor.previous = predecessor;
size += numNew;
return true;
}
/**
* Removes all of the elements from this list.
*/
public void clear() {
modCount++;
header.next = header.previous = header;
size = 0;
}
// Positional Access Operations
/**
* Returns the element at the specified position in this list.
*
* @param index index of element to return
* @return the element at the specified position in this list
*
* @throws IndexOutOfBoundsException if the specified index is is out of
* range (<code>index &lt; 0 || index &gt;= size()</code>)
*/
public Object get(int index) {
if (index < 0 || index >= size) {
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
}
Node e = header;
if (index < (size >> 1)) {
for (int i = 0; i <= index; i++) {
e = e.next;
}
}
else {
for (int i = size; i > index; i--) {
e = e.previous;
}
}
return e.element;
}
/**
* Replaces the element at the specified position in this list with the
* specified element.
*
* @param index index of element to replace
* @param element element to be stored at the specified position
* @return the element previously at the specified position
* @throws IndexOutOfBoundsException if the specified index is out of
* range (<code>index &lt; 0 || index &gt;= size()</code>)
*/
public Object set(int index, Object element) {
Node e = entry(index);
Object oldVal = e.element;
e.element = element;
return oldVal;
}
/**
* Inserts the specified element at the specified position in this list.
* Shifts the element currently at that position (if any) and any
* subsequent elements to the right (adds one to their indices).
*
* @param index index at which the specified element is to be inserted
* @param element element to be inserted
*
* @throws IndexOutOfBoundsException if the specified index is out of
* range (<code>index &lt; 0 || index &gt; size()</code>)
*/
public void add(int index, Object element) {
Node e = (index == size ? header : entry(index));
Node newNode;
if (cacheCount > 0) {
newNode = cacheHeader.next;
cacheHeader.next = newNode.next;
newNode.element = element;
newNode.next = e;
newNode.previous = e.previous;
}
else {
newNode = new Node(element, e, e.previous);
}
newNode.previous.next = newNode;
newNode.next.previous = newNode;
size++;
modCount++;
}
/**
* Removes the element at the specified position in this list. Shifts any
* subsequent elements to the left (subtracts one from their indices).
* Returns the element that was removed from the list.
*
* @param index the index of the element to removed
* @return the element previously at the specified position
*
* @throws IndexOutOfBoundsException if the specified index is out of
* range (<code>index &lt; 0 || index &gt;= size()</code>)
*/
public Object remove(int index) {
Node e = entry(index);
Object data = e.element;
remove(e);
return data;
}
/**
* Return the indexed entry.
*/
private Node entry(int index) {
if (index < 0 || index >= size) {
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
}
Node e = header;
if (index < (size >> 1)) {
for (int i = 0; i <= index; i++) {
e = e.next;
}
}
else {
for (int i = size; i > index; i--) {
e = e.previous;
}
}
return e;
}
// Search Operations
/**
* Returns the index in this list of the first occurrence of the
* specified element, or -1 if the List does not contain this
* element. More formally, returns the lowest index i such that
* <code>(o==null ? get(i)==null : o.equals(get(i)))</code>, or -1 if
* there is no such index.
*
* @param obj element to search for
* @return the index in this list of the first occurrence of the
* specified element, or -1 if the list does not contain this
* element
*/
public int indexOf(Object obj) {
int index = 0;
if (obj == null) {
for (Node e = header.next; e != header; e = e.next) {
if (e.element == null)
return index;
index++;
}
}
else {
for (Node e = header.next; e != header; e = e.next) {
if (obj.equals(e.element))
return index;
index++;
}
}
return -1;
}
/**
* Returns the index in this list of the last occurrence of the
* specified element, or -1 if the list does not contain this
* element. More formally, returns the highest index i such that
* <code>(o==null ? get(i)==null : o.equals(get(i)))</code>, or -1 if
* there is no such index.
*
* @param obj element to search for
* @return the index in this list of the last occurrence of the
* specified element, or -1 if the list does not contain this
* element
*/
public int lastIndexOf(Object obj) {
int index = size;
if (obj == null) {
for (Node e = header.previous; e != header; e = e.previous) {
index--;
if (e.element == null)
return index;
}
}
else {
for (Node e = header.previous; e != header; e = e.previous) {
index--;
if (obj.equals(e.element))
return index;
}
}
return -1;
}
/**
* Returns a list-iterator of the elements in this list (in proper
* sequence), starting at the specified position in the list.
* Obeys the general contract of <code>List.listIterator(int)</code>.<p>
* <p>
* The list-iterator is <i>fail-fast</i>: if the list is structurally
* modified at any time after the Iterator is created, in any way except
* through the list-iterator's own <code>remove</code> or <code>add</code>
* methods, the list-iterator will throw a
* <code>ConcurrentModificationException</code>. Thus, in the face of
* concurrent modification, the iterator fails quickly and cleanly, rather
* than risking arbitrary, non-deterministic behavior at an undetermined
* time in the future.
*
* @param index index of first element to be returned from the
* list-iterator (by a call to <code>next</code>)
* @return a ListIterator of the elements in this list (in proper
* sequence), starting at the specified position in the list
* @throws IndexOutOfBoundsException if index is out of range
* (<code>index &lt; 0 || index &gt; size()</code>)
* @see List#listIterator(int)
*/
public ListIterator listIterator(int index) {
return new ListItr(index);
}
private final class ListItr implements ListIterator {
private Node lastReturned = header;
private Node next;
private int nextIndex;
private int expectedModCount = modCount;
ListItr(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
if (index < (size >> 1)) {
next = header.next;
for (nextIndex = 0; nextIndex < index; nextIndex++)
next = next.next;
}
else {
next = header;
for (nextIndex = size; nextIndex > index; nextIndex--)
next = next.previous;
}
}
public boolean hasNext() {
return nextIndex != size;
}
public Object next() {
checkForComodification();
if (nextIndex == size)
throw new NoSuchElementException();
lastReturned = next;
next = next.next;
nextIndex++;
return lastReturned.element;
}
public boolean hasPrevious() {
return nextIndex != 0;
}
public Object previous() {
if (nextIndex == 0)
throw new NoSuchElementException();
lastReturned = next = next.previous;
nextIndex--;
checkForComodification();
return lastReturned.element;
}
public int nextIndex() {
return nextIndex;
}
public int previousIndex() {
return nextIndex - 1;
}
public void remove() {
checkForComodification();
try {
NodeCachingLinkedList.this.remove(lastReturned);
}
catch (NoSuchElementException e) {
throw new IllegalStateException();
}
if (next == lastReturned)
next = lastReturned.next;
else
nextIndex--;
lastReturned = header;
expectedModCount++;
}
public void set(Object o) {
if (lastReturned == header)
throw new IllegalStateException();
checkForComodification();
lastReturned.element = o;
}
public void add(Object o) {
checkForComodification();
lastReturned = header;
Node newNode;
if (cacheCount > 0) {
newNode = cacheHeader.next;
cacheHeader.next = newNode.next;
newNode.element = o;
newNode.next = next;
newNode.previous = next.previous;
}
else {
newNode = new Node(o, next, next.previous);
}
newNode.previous.next = newNode;
newNode.next.previous = newNode;
size++;
modCount++;
nextIndex++;
expectedModCount++;
}
private void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
private final static class Node implements Serializable {
Object element;
Node next;
Node previous;
Node(Object element, Node next, Node previous) {
this.element = element;
this.next = next;
this.previous = previous;
}
}
private Node addsBefore(Object o, Node e) {
Node newNode;
if (cacheCount > 0) {
newNode = cacheHeader.next;
cacheHeader.next = newNode.next;
newNode.element = o;
newNode.next = e;
newNode.previous = e.previous;
}
else {
newNode = new Node(o, e, e.previous);
}
newNode.previous.next = newNode;
newNode.next.previous = newNode;
size++;
modCount++;
return newNode;
}
private void remove(Node e) {
if (e == header) {
throw new NoSuchElementException();
}
e.previous.next = e.next;
e.next.previous = e.previous;
size--;
modCount++;
if (cacheCount < maximumCacheSize) {
e.element = null;
e.previous = null;
e.next = cacheHeader.next;
cacheHeader.next = e;
cacheCount++;
}
}
/**
* Returns a shallow copy of this <code>NodeCachingLinkedList</code>. (The elements
* themselves are not cloned.)
*
* @return a shallow copy of this <code>NodeCachingLinkedList</code> instance
*/
public Object clone() {
NodeCachingLinkedList clone = new NodeCachingLinkedList();
clone.setMaximumCacheSize(maximumCacheSize);
// Initialize clone with our elements
for (Node e = header.next; e != header; e = e.next) {
clone.add(e.element);
}
return clone;
}
/**
* Returns an array containing all of the elements in this list
* in the correct order.
*
* @return an array containing all of the elements in this list
* in the correct order
*/
public Object[] toArray() {
Object[] result = new Object[size];
int i = 0;
for (Node e = header.next; e != header; e = e.next)
result[i++] = e.element;
return result;
}
/**
* Returns an array containing all of the elements in this list in
* the correct order; the runtime type of the returned array is that of
* the specified array. If the list fits in the specified array, it
* is returned therein. Otherwise, a new array is allocated with the
* runtime type of the specified array and the size of this list.<p>
* <p>
* If the list fits in the specified array with room to spare
* (i.e., the array has more elements than the list),
* the element in the array immediately following the end of the
* collection is set to null. This is useful in determining the length
* of the list <i>only</i> if the caller knows that the list
* does not contain any null elements.
*
* @param a the array into which the elements of the list are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose
* @return an array containing the elements of the list
* @throws ArrayStoreException if the runtime type of a is not a
* supertype of the runtime type of every element in this list
* @throws NullPointerException if the specified array is null
*/
public Object[] toArray(Object a[]) {
if (a.length < size)
a = (Object[]) java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), size);
int i = 0;
for (Node e = header.next; e != header; e = e.next)
a[i++] = e.element;
if (a.length > size)
a[size] = null;
return a;
}
}