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:
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 setFast(true)
) after initialization
* is complete.
NOTE: If you are creating and accessing a
* TreeMap
only within a single thread, you should use
* java.util.TreeMap
directly (with no synchronization), for
* maximum performance.
NOTE: This class is not cross-platform. * Using it may cause unexpected failures on some architectures. * 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 * * Double-Checked Locking Idiom Is Broken Declaration.
* * @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 *null
if the map contains no mapping for this key, or if
* there is a mapping with a value of null
. Use the
* 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 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 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 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 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
* 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 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 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 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;
}
}
}