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Commons Collections example source code file (FastTreeMap.java)

This example Commons Collections source code file (FastTreeMap.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

collection, collectionview, collectionviewiterator, fasttreemap, fasttreemap, iterator, iterator, map, object, object, set, sortedmap, treemap, treemap, util

The Commons Collections FastTreeMap.java source code

/*
 *  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.commons.collections;

import java.util.Collection;
import java.util.Comparator;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;

/**
 * <p>A customized implementation of java.util.TreeMap designed
 * to operate in a multithreaded environment where the large majority of
 * method calls are read-only, instead of structural changes.  When operating
 * in "fast" mode, read calls are non-synchronized and write calls perform the
 * following steps:</p>
 * <ul>
 * <li>Clone the existing collection
 * <li>Perform the modification on the clone
 * <li>Replace the existing collection with the (modified) clone
 * </ul>
 * <p>When first created, objects of this class default to "slow" mode, where
 * all accesses of any type are synchronized but no cloning takes place.  This
 * is appropriate for initially populating the collection, followed by a switch
 * to "fast" mode (by calling <code>setFast(true)) after initialization
 * is complete.</p>
 *
 * <p>NOTE: If you are creating and accessing a
 * <code>TreeMap only within a single thread, you should use
 * <code>java.util.TreeMap directly (with no synchronization), for
 * maximum performance.</p>
 *
 * <p>NOTE: This class is not cross-platform.  
 * Using it may cause unexpected failures on some architectures.</i>
 * It suffers from the same problems as the double-checked locking idiom.  
 * In particular, the instruction that clones the internal collection and the 
 * instruction that sets the internal reference to the clone can be executed 
 * or perceived out-of-order.  This means that any read operation might fail 
 * unexpectedly, as it may be reading the state of the internal collection
 * before the internal collection is fully formed.
 * For more information on the double-checked locking idiom, see the
 * <a href="http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html">
 * Double-Checked Locking Idiom Is Broken Declaration</a>.

* * @since Commons Collections 1.0 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $ * * @author Craig R. McClanahan * @author Stephen Colebourne */ public class FastTreeMap extends TreeMap { /** * The underlying map we are managing. */ protected TreeMap map = null; /** * Are we operating in "fast" mode? */ protected boolean fast = false; // Constructors // ---------------------------------------------------------------------- /** * Construct a an empty map. */ public FastTreeMap() { super(); this.map = new TreeMap(); } /** * Construct an empty map with the specified comparator. * * @param comparator the comparator to use for ordering tree elements */ public FastTreeMap(Comparator comparator) { super(); this.map = new TreeMap(comparator); } /** * Construct a new map with the same mappings as the specified map, * sorted according to the keys's natural order * * @param map the map whose mappings are to be copied */ public FastTreeMap(Map map) { super(); this.map = new TreeMap(map); } /** * Construct a new map with the same mappings as the specified map, * sorted according to the same ordering * * @param map the map whose mappings are to be copied */ public FastTreeMap(SortedMap map) { super(); this.map = new TreeMap(map); } // Property access // ---------------------------------------------------------------------- /** * Returns true if this map is operating in fast mode. * * @return true if this map is operating in fast mode */ public boolean getFast() { return (this.fast); } /** * Sets whether this map is operating in fast mode. * * @param fast true if this map should operate in fast mode */ public void setFast(boolean fast) { this.fast = fast; } // Map access // ---------------------------------------------------------------------- // These methods can forward straight to the wrapped Map in 'fast' mode. // (because they are query methods) /** * Return the value to which this map maps the specified key. Returns * <code>null if the map contains no mapping for this key, or if * there is a mapping with a value of <code>null. Use the * <code>containsKey() method to disambiguate these cases. * * @param key the key whose value is to be returned * @return the value mapped to that key, or null */ public Object get(Object key) { if (fast) { return (map.get(key)); } else { synchronized (map) { return (map.get(key)); } } } /** * Return the number of key-value mappings in this map. * * @return the current size of the map */ public int size() { if (fast) { return (map.size()); } else { synchronized (map) { return (map.size()); } } } /** * Return <code>true if this map contains no mappings. * * @return is the map currently empty */ public boolean isEmpty() { if (fast) { return (map.isEmpty()); } else { synchronized (map) { return (map.isEmpty()); } } } /** * Return <code>true if this map contains a mapping for the * specified key. * * @param key the key to be searched for * @return true if the map contains the key */ public boolean containsKey(Object key) { if (fast) { return (map.containsKey(key)); } else { synchronized (map) { return (map.containsKey(key)); } } } /** * Return <code>true if this map contains one or more keys mapping * to the specified value. * * @param value the value to be searched for * @return true if the map contains the value */ public boolean containsValue(Object value) { if (fast) { return (map.containsValue(value)); } else { synchronized (map) { return (map.containsValue(value)); } } } /** * Return the comparator used to order this map, or <code>null * if this map uses its keys' natural order. * * @return the comparator used to order the map, or null if natural order */ public Comparator comparator() { if (fast) { return (map.comparator()); } else { synchronized (map) { return (map.comparator()); } } } /** * Return the first (lowest) key currently in this sorted map. * * @return the first key in the map */ public Object firstKey() { if (fast) { return (map.firstKey()); } else { synchronized (map) { return (map.firstKey()); } } } /** * Return the last (highest) key currently in this sorted map. * * @return the last key in the map */ public Object lastKey() { if (fast) { return (map.lastKey()); } else { synchronized (map) { return (map.lastKey()); } } } // Map modification // ---------------------------------------------------------------------- // These methods perform special behaviour in 'fast' mode. // The map is cloned, updated and then assigned back. // See the comments at the top as to why this won't always work. /** * Associate the specified value with the specified key in this map. * If the map previously contained a mapping for this key, the old * value is replaced and returned. * * @param key the key with which the value is to be associated * @param value the value to be associated with this key * @return the value previously mapped to the key, or null */ public Object put(Object key, Object value) { if (fast) { synchronized (this) { TreeMap temp = (TreeMap) map.clone(); Object result = temp.put(key, value); map = temp; return (result); } } else { synchronized (map) { return (map.put(key, value)); } } } /** * Copy all of the mappings from the specified map to this one, replacing * any mappings with the same keys. * * @param in the map whose mappings are to be copied */ public void putAll(Map in) { if (fast) { synchronized (this) { TreeMap temp = (TreeMap) map.clone(); temp.putAll(in); map = temp; } } else { synchronized (map) { map.putAll(in); } } } /** * Remove any mapping for this key, and return any previously * mapped value. * * @param key the key whose mapping is to be removed * @return the value removed, or null */ public Object remove(Object key) { if (fast) { synchronized (this) { TreeMap temp = (TreeMap) map.clone(); Object result = temp.remove(key); map = temp; return (result); } } else { synchronized (map) { return (map.remove(key)); } } } /** * Remove all mappings from this map. */ public void clear() { if (fast) { synchronized (this) { map = new TreeMap(); } } else { synchronized (map) { map.clear(); } } } // Basic object methods // ---------------------------------------------------------------------- /** * Compare the specified object with this list for equality. This * implementation uses exactly the code that is used to define the * list equals function in the documentation for the * <code>Map.equals method. * * @param o the object to be compared to this list * @return true if the two maps are equal */ public boolean equals(Object o) { // Simple tests that require no synchronization if (o == this) { return (true); } else if (!(o instanceof Map)) { return (false); } Map mo = (Map) o; // Compare the two maps for equality if (fast) { if (mo.size() != map.size()) { return (false); } Iterator i = map.entrySet().iterator(); while (i.hasNext()) { Map.Entry e = (Map.Entry) i.next(); Object key = e.getKey(); Object value = e.getValue(); if (value == null) { if (!(mo.get(key) == null && mo.containsKey(key))) { return (false); } } else { if (!value.equals(mo.get(key))) { return (false); } } } return (true); } else { synchronized (map) { if (mo.size() != map.size()) { return (false); } Iterator i = map.entrySet().iterator(); while (i.hasNext()) { Map.Entry e = (Map.Entry) i.next(); Object key = e.getKey(); Object value = e.getValue(); if (value == null) { if (!(mo.get(key) == null && mo.containsKey(key))) { return (false); } } else { if (!value.equals(mo.get(key))) { return (false); } } } return (true); } } } /** * Return the hash code value for this map. This implementation uses * exactly the code that is used to define the list hash function in the * documentation for the <code>Map.hashCode method. * * @return a suitable integer hash code */ public int hashCode() { if (fast) { int h = 0; Iterator i = map.entrySet().iterator(); while (i.hasNext()) { h += i.next().hashCode(); } return (h); } else { synchronized (map) { int h = 0; Iterator i = map.entrySet().iterator(); while (i.hasNext()) { h += i.next().hashCode(); } return (h); } } } /** * Return a shallow copy of this <code>FastTreeMap instance. * The keys and values themselves are not copied. * * @return a clone of this map */ public Object clone() { FastTreeMap results = null; if (fast) { results = new FastTreeMap(map); } else { synchronized (map) { results = new FastTreeMap(map); } } results.setFast(getFast()); return (results); } // Sub map views // ---------------------------------------------------------------------- /** * Return a view of the portion of this map whose keys are strictly * less than the specified key. * * @param key Key higher than any in the returned map * @return a head map */ public SortedMap headMap(Object key) { if (fast) { return (map.headMap(key)); } else { synchronized (map) { return (map.headMap(key)); } } } /** * Return a view of the portion of this map whose keys are in the * range fromKey (inclusive) to toKey (exclusive). * * @param fromKey Lower limit of keys for the returned map * @param toKey Upper limit of keys for the returned map * @return a sub map */ public SortedMap subMap(Object fromKey, Object toKey) { if (fast) { return (map.subMap(fromKey, toKey)); } else { synchronized (map) { return (map.subMap(fromKey, toKey)); } } } /** * Return a view of the portion of this map whose keys are greater than * or equal to the specified key. * * @param key Key less than or equal to any in the returned map * @return a tail map */ public SortedMap tailMap(Object key) { if (fast) { return (map.tailMap(key)); } else { synchronized (map) { return (map.tailMap(key)); } } } // Map views // ---------------------------------------------------------------------- /** * Return a collection view of the mappings contained in this map. Each * element in the returned collection is a <code>Map.Entry. */ public Set entrySet() { return new EntrySet(); } /** * Return a set view of the keys contained in this map. */ public Set keySet() { return new KeySet(); } /** * Return a collection view of the values contained in this map. */ public Collection values() { return new Values(); } // Map view inner classes // ---------------------------------------------------------------------- /** * Abstract collection implementation shared by keySet(), values() and entrySet(). */ private abstract class CollectionView implements Collection { public CollectionView() { } protected abstract Collection get(Map map); protected abstract Object iteratorNext(Map.Entry entry); public void clear() { if (fast) { synchronized (FastTreeMap.this) { map = new TreeMap(); } } else { synchronized (map) { get(map).clear(); } } } public boolean remove(Object o) { if (fast) { synchronized (FastTreeMap.this) { TreeMap temp = (TreeMap) map.clone(); boolean r = get(temp).remove(o); map = temp; return r; } } else { synchronized (map) { return get(map).remove(o); } } } public boolean removeAll(Collection o) { if (fast) { synchronized (FastTreeMap.this) { TreeMap temp = (TreeMap) map.clone(); boolean r = get(temp).removeAll(o); map = temp; return r; } } else { synchronized (map) { return get(map).removeAll(o); } } } public boolean retainAll(Collection o) { if (fast) { synchronized (FastTreeMap.this) { TreeMap temp = (TreeMap) map.clone(); boolean r = get(temp).retainAll(o); map = temp; return r; } } else { synchronized (map) { return get(map).retainAll(o); } } } public int size() { if (fast) { return get(map).size(); } else { synchronized (map) { return get(map).size(); } } } public boolean isEmpty() { if (fast) { return get(map).isEmpty(); } else { synchronized (map) { return get(map).isEmpty(); } } } public boolean contains(Object o) { if (fast) { return get(map).contains(o); } else { synchronized (map) { return get(map).contains(o); } } } public boolean containsAll(Collection o) { if (fast) { return get(map).containsAll(o); } else { synchronized (map) { return get(map).containsAll(o); } } } public Object[] toArray(Object[] o) { if (fast) { return get(map).toArray(o); } else { synchronized (map) { return get(map).toArray(o); } } } public Object[] toArray() { if (fast) { return get(map).toArray(); } else { synchronized (map) { return get(map).toArray(); } } } public boolean equals(Object o) { if (o == this) return true; if (fast) { return get(map).equals(o); } else { synchronized (map) { return get(map).equals(o); } } } public int hashCode() { if (fast) { return get(map).hashCode(); } else { synchronized (map) { return get(map).hashCode(); } } } public boolean add(Object o) { throw new UnsupportedOperationException(); } public boolean addAll(Collection c) { throw new UnsupportedOperationException(); } public Iterator iterator() { return new CollectionViewIterator(); } private class CollectionViewIterator implements Iterator { private Map expected; private Map.Entry lastReturned = null; private Iterator iterator; public CollectionViewIterator() { this.expected = map; this.iterator = expected.entrySet().iterator(); } public boolean hasNext() { if (expected != map) { throw new ConcurrentModificationException(); } return iterator.hasNext(); } public Object next() { if (expected != map) { throw new ConcurrentModificationException(); } lastReturned = (Map.Entry)iterator.next(); return iteratorNext(lastReturned); } public void remove() { if (lastReturned == null) { throw new IllegalStateException(); } if (fast) { synchronized (FastTreeMap.this) { if (expected != map) { throw new ConcurrentModificationException(); } FastTreeMap.this.remove(lastReturned.getKey()); lastReturned = null; expected = map; } } else { iterator.remove(); lastReturned = null; } } } } /** * Set implementation over the keys of the FastTreeMap */ private class KeySet extends CollectionView implements Set { protected Collection get(Map map) { return map.keySet(); } protected Object iteratorNext(Map.Entry entry) { return entry.getKey(); } } /** * Collection implementation over the values of the FastTreeMap */ private class Values extends CollectionView { protected Collection get(Map map) { return map.values(); } protected Object iteratorNext(Map.Entry entry) { return entry.getValue(); } } /** * Set implementation over the entries of the FastTreeMap */ private class EntrySet extends CollectionView implements Set { protected Collection get(Map map) { return map.entrySet(); } protected Object iteratorNext(Map.Entry entry) { return entry; } } }

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