org.apache.commons.collections.map.Flat3Map Maven / Gradle / Ivy
/*
* 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.map;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import org.apache.commons.collections.IterableMap;
import org.apache.commons.collections.MapIterator;
import org.apache.commons.collections.ResettableIterator;
import org.apache.commons.collections.iterators.EmptyIterator;
import org.apache.commons.collections.iterators.EmptyMapIterator;
/**
* A Map implementation that stores data in simple fields until
* the size is greater than 3.
*
* This map is designed for performance and can outstrip HashMap.
* It also has good garbage collection characteristics.
*
* - Optimised for operation at size 3 or less.
*
- Still works well once size 3 exceeded.
*
- Gets at size 3 or less are about 0-10% faster than HashMap,
*
- Puts at size 3 or less are over 4 times faster than HashMap.
*
- Performance 5% slower than HashMap once size 3 exceeded once.
*
* The design uses two distinct modes of operation - flat and delegate.
* While the map is size 3 or less, operations map straight onto fields using
* switch statements. Once size 4 is reached, the map switches to delegate mode
* and only switches back when cleared. In delegate mode, all operations are
* forwarded straight to a HashMap resulting in the 5% performance loss.
*
* The performance gains on puts are due to not needing to create a Map Entry
* object. This is a large saving not only in performance but in garbage collection.
*
* Whilst in flat mode this map is also easy for the garbage collector to dispatch.
* This is because it contains no complex objects or arrays which slow the progress.
*
* Do not use Flat3Map if the size is likely to grow beyond 3.
*
* Note that Flat3Map is not synchronized and is not thread-safe.
* If you wish to use this map from multiple threads concurrently, you must use
* appropriate synchronization. The simplest approach is to wrap this map
* using {@link java.util.Collections#synchronizedMap(Map)}. This class may throw
* exceptions when accessed by concurrent threads without synchronization.
*
* @since Commons Collections 3.0
* @version $Revision: 1713293 $ $Date: 2015-11-08 22:04:34 +0100 (Sun, 08 Nov 2015) $
*
* @author Stephen Colebourne
*/
public class Flat3Map implements IterableMap, Serializable, Cloneable {
/** Serialization version */
private static final long serialVersionUID = -6701087419741928296L;
/** The size of the map, used while in flat mode */
private transient int size;
/** Hash, used while in flat mode */
private transient int hash1;
/** Hash, used while in flat mode */
private transient int hash2;
/** Hash, used while in flat mode */
private transient int hash3;
/** Key, used while in flat mode */
private transient Object key1;
/** Key, used while in flat mode */
private transient Object key2;
/** Key, used while in flat mode */
private transient Object key3;
/** Value, used while in flat mode */
private transient Object value1;
/** Value, used while in flat mode */
private transient Object value2;
/** Value, used while in flat mode */
private transient Object value3;
/** Map, used while in delegate mode */
private transient AbstractHashedMap delegateMap;
/**
* Constructor.
*/
public Flat3Map() {
super();
}
/**
* Constructor copying elements from another map.
*
* @param map the map to copy
* @throws NullPointerException if the map is null
*/
public Flat3Map(Map map) {
super();
putAll(map);
}
//-----------------------------------------------------------------------
/**
* Gets the value mapped to the key specified.
*
* @param key the key
* @return the mapped value, null if no match
*/
public Object get(Object key) {
if (delegateMap != null) {
return delegateMap.get(key);
}
if (key == null) {
switch (size) {
// drop through
case 3:
if (key3 == null) return value3;
case 2:
if (key2 == null) return value2;
case 1:
if (key1 == null) return value1;
}
} else {
if (size > 0) {
int hashCode = key.hashCode();
switch (size) {
// drop through
case 3:
if (hash3 == hashCode && key.equals(key3)) return value3;
case 2:
if (hash2 == hashCode && key.equals(key2)) return value2;
case 1:
if (hash1 == hashCode && key.equals(key1)) return value1;
}
}
}
return null;
}
/**
* Gets the size of the map.
*
* @return the size
*/
public int size() {
if (delegateMap != null) {
return delegateMap.size();
}
return size;
}
/**
* Checks whether the map is currently empty.
*
* @return true if the map is currently size zero
*/
public boolean isEmpty() {
return (size() == 0);
}
//-----------------------------------------------------------------------
/**
* Checks whether the map contains the specified key.
*
* @param key the key to search for
* @return true if the map contains the key
*/
public boolean containsKey(Object key) {
if (delegateMap != null) {
return delegateMap.containsKey(key);
}
if (key == null) {
switch (size) { // drop through
case 3:
if (key3 == null) return true;
case 2:
if (key2 == null) return true;
case 1:
if (key1 == null) return true;
}
} else {
if (size > 0) {
int hashCode = key.hashCode();
switch (size) { // drop through
case 3:
if (hash3 == hashCode && key.equals(key3)) return true;
case 2:
if (hash2 == hashCode && key.equals(key2)) return true;
case 1:
if (hash1 == hashCode && key.equals(key1)) return true;
}
}
}
return false;
}
/**
* Checks whether the map contains the specified value.
*
* @param value the value to search for
* @return true if the map contains the key
*/
public boolean containsValue(Object value) {
if (delegateMap != null) {
return delegateMap.containsValue(value);
}
if (value == null) { // drop through
switch (size) {
case 3:
if (value3 == null) return true;
case 2:
if (value2 == null) return true;
case 1:
if (value1 == null) return true;
}
} else {
switch (size) { // drop through
case 3:
if (value.equals(value3)) return true;
case 2:
if (value.equals(value2)) return true;
case 1:
if (value.equals(value1)) return true;
}
}
return false;
}
//-----------------------------------------------------------------------
/**
* Puts a key-value mapping into this map.
*
* @param key the key to add
* @param value the value to add
* @return the value previously mapped to this key, null if none
*/
public Object put(Object key, Object value) {
if (delegateMap != null) {
return delegateMap.put(key, value);
}
// change existing mapping
if (key == null) {
switch (size) { // drop through
case 3:
if (key3 == null) {
Object old = value3;
value3 = value;
return old;
}
case 2:
if (key2 == null) {
Object old = value2;
value2 = value;
return old;
}
case 1:
if (key1 == null) {
Object old = value1;
value1 = value;
return old;
}
}
} else {
if (size > 0) {
int hashCode = key.hashCode();
switch (size) { // drop through
case 3:
if (hash3 == hashCode && key.equals(key3)) {
Object old = value3;
value3 = value;
return old;
}
case 2:
if (hash2 == hashCode && key.equals(key2)) {
Object old = value2;
value2 = value;
return old;
}
case 1:
if (hash1 == hashCode && key.equals(key1)) {
Object old = value1;
value1 = value;
return old;
}
}
}
}
// add new mapping
switch (size) {
default:
convertToMap();
delegateMap.put(key, value);
return null;
case 2:
hash3 = (key == null ? 0 : key.hashCode());
key3 = key;
value3 = value;
break;
case 1:
hash2 = (key == null ? 0 : key.hashCode());
key2 = key;
value2 = value;
break;
case 0:
hash1 = (key == null ? 0 : key.hashCode());
key1 = key;
value1 = value;
break;
}
size++;
return null;
}
/**
* Puts all the values from the specified map into this map.
*
* @param map the map to add
* @throws NullPointerException if the map is null
*/
public void putAll(Map map) {
int size = map.size();
if (size == 0) {
return;
}
if (delegateMap != null) {
delegateMap.putAll(map);
return;
}
if (size < 4) {
for (Iterator it = map.entrySet().iterator(); it.hasNext();) {
Map.Entry entry = (Map.Entry) it.next();
put(entry.getKey(), entry.getValue());
}
} else {
convertToMap();
delegateMap.putAll(map);
}
}
/**
* Converts the flat map data to a map.
*/
private void convertToMap() {
delegateMap = createDelegateMap();
switch (size) { // drop through
case 3:
delegateMap.put(key3, value3);
case 2:
delegateMap.put(key2, value2);
case 1:
delegateMap.put(key1, value1);
}
size = 0;
hash1 = hash2 = hash3 = 0;
key1 = key2 = key3 = null;
value1 = value2 = value3 = null;
}
/**
* Create an instance of the map used for storage when in delegation mode.
*
* This can be overridden by subclasses to provide a different map implementation.
* Not every AbstractHashedMap is suitable, identity and reference based maps
* would be poor choices.
*
* @return a new AbstractHashedMap or subclass
* @since Commons Collections 3.1
*/
protected AbstractHashedMap createDelegateMap() {
return new HashedMap();
}
/**
* Removes the specified mapping from this map.
*
* @param key the mapping to remove
* @return the value mapped to the removed key, null if key not in map
*/
public Object remove(Object key) {
if (delegateMap != null) {
return delegateMap.remove(key);
}
if (size == 0) {
return null;
}
if (key == null) {
switch (size) { // drop through
case 3:
if (key3 == null) {
Object old = value3;
hash3 = 0;
key3 = null;
value3 = null;
size = 2;
return old;
}
if (key2 == null) {
Object old = value2;
hash2 = hash3;
key2 = key3;
value2 = value3;
hash3 = 0;
key3 = null;
value3 = null;
size = 2;
return old;
}
if (key1 == null) {
Object old = value1;
hash1 = hash3;
key1 = key3;
value1 = value3;
hash3 = 0;
key3 = null;
value3 = null;
size = 2;
return old;
}
return null;
case 2:
if (key2 == null) {
Object old = value2;
hash2 = 0;
key2 = null;
value2 = null;
size = 1;
return old;
}
if (key1 == null) {
Object old = value1;
hash1 = hash2;
key1 = key2;
value1 = value2;
hash2 = 0;
key2 = null;
value2 = null;
size = 1;
return old;
}
return null;
case 1:
if (key1 == null) {
Object old = value1;
hash1 = 0;
key1 = null;
value1 = null;
size = 0;
return old;
}
}
} else {
if (size > 0) {
int hashCode = key.hashCode();
switch (size) { // drop through
case 3:
if (hash3 == hashCode && key.equals(key3)) {
Object old = value3;
hash3 = 0;
key3 = null;
value3 = null;
size = 2;
return old;
}
if (hash2 == hashCode && key.equals(key2)) {
Object old = value2;
hash2 = hash3;
key2 = key3;
value2 = value3;
hash3 = 0;
key3 = null;
value3 = null;
size = 2;
return old;
}
if (hash1 == hashCode && key.equals(key1)) {
Object old = value1;
hash1 = hash3;
key1 = key3;
value1 = value3;
hash3 = 0;
key3 = null;
value3 = null;
size = 2;
return old;
}
return null;
case 2:
if (hash2 == hashCode && key.equals(key2)) {
Object old = value2;
hash2 = 0;
key2 = null;
value2 = null;
size = 1;
return old;
}
if (hash1 == hashCode && key.equals(key1)) {
Object old = value1;
hash1 = hash2;
key1 = key2;
value1 = value2;
hash2 = 0;
key2 = null;
value2 = null;
size = 1;
return old;
}
return null;
case 1:
if (hash1 == hashCode && key.equals(key1)) {
Object old = value1;
hash1 = 0;
key1 = null;
value1 = null;
size = 0;
return old;
}
}
}
}
return null;
}
/**
* Clears the map, resetting the size to zero and nullifying references
* to avoid garbage collection issues.
*/
public void clear() {
if (delegateMap != null) {
delegateMap.clear(); // should aid gc
delegateMap = null; // switch back to flat mode
} else {
size = 0;
hash1 = hash2 = hash3 = 0;
key1 = key2 = key3 = null;
value1 = value2 = value3 = null;
}
}
//-----------------------------------------------------------------------
/**
* Gets an iterator over the map.
* Changes made to the iterator affect this map.
*
* A MapIterator returns the keys in the map. It also provides convenient
* methods to get the key and value, and set the value.
* It avoids the need to create an entrySet/keySet/values object.
* It also avoids creating the Map Entry object.
*
* @return the map iterator
*/
public MapIterator mapIterator() {
if (delegateMap != null) {
return delegateMap.mapIterator();
}
if (size == 0) {
return EmptyMapIterator.INSTANCE;
}
return new FlatMapIterator(this);
}
/**
* FlatMapIterator
*/
static class FlatMapIterator implements MapIterator, ResettableIterator {
private final Flat3Map parent;
private int nextIndex = 0;
private boolean canRemove = false;
FlatMapIterator(Flat3Map parent) {
super();
this.parent = parent;
}
public boolean hasNext() {
return (nextIndex < parent.size);
}
public Object next() {
if (hasNext() == false) {
throw new NoSuchElementException(AbstractHashedMap.NO_NEXT_ENTRY);
}
canRemove = true;
nextIndex++;
return getKey();
}
public void remove() {
if (canRemove == false) {
throw new IllegalStateException(AbstractHashedMap.REMOVE_INVALID);
}
parent.remove(getKey());
nextIndex--;
canRemove = false;
}
public Object getKey() {
if (canRemove == false) {
throw new IllegalStateException(AbstractHashedMap.GETKEY_INVALID);
}
switch (nextIndex) {
case 3:
return parent.key3;
case 2:
return parent.key2;
case 1:
return parent.key1;
}
throw new IllegalStateException("Invalid map index");
}
public Object getValue() {
if (canRemove == false) {
throw new IllegalStateException(AbstractHashedMap.GETVALUE_INVALID);
}
switch (nextIndex) {
case 3:
return parent.value3;
case 2:
return parent.value2;
case 1:
return parent.value1;
}
throw new IllegalStateException("Invalid map index");
}
public Object setValue(Object value) {
if (canRemove == false) {
throw new IllegalStateException(AbstractHashedMap.SETVALUE_INVALID);
}
Object old = getValue();
switch (nextIndex) {
case 3:
parent.value3 = value;
case 2:
parent.value2 = value;
case 1:
parent.value1 = value;
}
return old;
}
public void reset() {
nextIndex = 0;
canRemove = false;
}
public String toString() {
if (canRemove) {
return "Iterator[" + getKey() + "=" + getValue() + "]";
} else {
return "Iterator[]";
}
}
}
/**
* Gets the entrySet view of the map.
* Changes made to the view affect this map.
* The Map Entry is not an independent object and changes as the
* iterator progresses.
* To simply iterate through the entries, use {@link #mapIterator()}.
*
* @return the entrySet view
*/
public Set entrySet() {
if (delegateMap != null) {
return delegateMap.entrySet();
}
return new EntrySet(this);
}
/**
* EntrySet
*/
static class EntrySet extends AbstractSet {
private final Flat3Map parent;
EntrySet(Flat3Map parent) {
super();
this.parent = parent;
}
public int size() {
return parent.size();
}
public void clear() {
parent.clear();
}
public boolean remove(Object obj) {
if (obj instanceof Map.Entry == false) {
return false;
}
Map.Entry entry = (Map.Entry) obj;
Object key = entry.getKey();
boolean result = parent.containsKey(key);
parent.remove(key);
return result;
}
public Iterator iterator() {
if (parent.delegateMap != null) {
return parent.delegateMap.entrySet().iterator();
}
if (parent.size() == 0) {
return EmptyIterator.INSTANCE;
}
return new EntrySetIterator(parent);
}
}
/**
* EntrySetIterator and MapEntry
*/
static class EntrySetIterator implements Iterator, Map.Entry {
private final Flat3Map parent;
private int nextIndex = 0;
private boolean canRemove = false;
EntrySetIterator(Flat3Map parent) {
super();
this.parent = parent;
}
public boolean hasNext() {
return (nextIndex < parent.size);
}
public Object next() {
if (hasNext() == false) {
throw new NoSuchElementException(AbstractHashedMap.NO_NEXT_ENTRY);
}
canRemove = true;
nextIndex++;
return this;
}
public void remove() {
if (canRemove == false) {
throw new IllegalStateException(AbstractHashedMap.REMOVE_INVALID);
}
parent.remove(getKey());
nextIndex--;
canRemove = false;
}
public Object getKey() {
if (canRemove == false) {
throw new IllegalStateException(AbstractHashedMap.GETKEY_INVALID);
}
switch (nextIndex) {
case 3:
return parent.key3;
case 2:
return parent.key2;
case 1:
return parent.key1;
}
throw new IllegalStateException("Invalid map index");
}
public Object getValue() {
if (canRemove == false) {
throw new IllegalStateException(AbstractHashedMap.GETVALUE_INVALID);
}
switch (nextIndex) {
case 3:
return parent.value3;
case 2:
return parent.value2;
case 1:
return parent.value1;
}
throw new IllegalStateException("Invalid map index");
}
public Object setValue(Object value) {
if (canRemove == false) {
throw new IllegalStateException(AbstractHashedMap.SETVALUE_INVALID);
}
Object old = getValue();
switch (nextIndex) {
case 3:
parent.value3 = value;
break;
case 2:
parent.value2 = value;
break;
case 1:
parent.value1 = value;
break;
}
return old;
}
public boolean equals(Object obj) {
if (canRemove == false) {
return false;
}
if (obj instanceof Map.Entry == false) {
return false;
}
Map.Entry other = (Map.Entry) obj;
Object key = getKey();
Object value = getValue();
return (key == null ? other.getKey() == null : key.equals(other.getKey())) &&
(value == null ? other.getValue() == null : value.equals(other.getValue()));
}
public int hashCode() {
if (canRemove == false) {
return 0;
}
Object key = getKey();
Object value = getValue();
return (key == null ? 0 : key.hashCode()) ^
(value == null ? 0 : value.hashCode());
}
public String toString() {
if (canRemove) {
return getKey() + "=" + getValue();
} else {
return "";
}
}
}
/**
* Gets the keySet view of the map.
* Changes made to the view affect this map.
* To simply iterate through the keys, use {@link #mapIterator()}.
*
* @return the keySet view
*/
public Set keySet() {
if (delegateMap != null) {
return delegateMap.keySet();
}
return new KeySet(this);
}
/**
* KeySet
*/
static class KeySet extends AbstractSet {
private final Flat3Map parent;
KeySet(Flat3Map parent) {
super();
this.parent = parent;
}
public int size() {
return parent.size();
}
public void clear() {
parent.clear();
}
public boolean contains(Object key) {
return parent.containsKey(key);
}
public boolean remove(Object key) {
boolean result = parent.containsKey(key);
parent.remove(key);
return result;
}
public Iterator iterator() {
if (parent.delegateMap != null) {
return parent.delegateMap.keySet().iterator();
}
if (parent.size() == 0) {
return EmptyIterator.INSTANCE;
}
return new KeySetIterator(parent);
}
}
/**
* KeySetIterator
*/
static class KeySetIterator extends EntrySetIterator {
KeySetIterator(Flat3Map parent) {
super(parent);
}
public Object next() {
super.next();
return getKey();
}
}
/**
* Gets the values view of the map.
* Changes made to the view affect this map.
* To simply iterate through the values, use {@link #mapIterator()}.
*
* @return the values view
*/
public Collection values() {
if (delegateMap != null) {
return delegateMap.values();
}
return new Values(this);
}
/**
* Values
*/
static class Values extends AbstractCollection {
private final Flat3Map parent;
Values(Flat3Map parent) {
super();
this.parent = parent;
}
public int size() {
return parent.size();
}
public void clear() {
parent.clear();
}
public boolean contains(Object value) {
return parent.containsValue(value);
}
public Iterator iterator() {
if (parent.delegateMap != null) {
return parent.delegateMap.values().iterator();
}
if (parent.size() == 0) {
return EmptyIterator.INSTANCE;
}
return new ValuesIterator(parent);
}
}
/**
* ValuesIterator
*/
static class ValuesIterator extends EntrySetIterator {
ValuesIterator(Flat3Map parent) {
super(parent);
}
public Object next() {
super.next();
return getValue();
}
}
//-----------------------------------------------------------------------
/**
* Write the map out using a custom routine.
*/
private void writeObject(ObjectOutputStream out) throws IOException {
out.defaultWriteObject();
out.writeInt(size());
for (MapIterator it = mapIterator(); it.hasNext();) {
out.writeObject(it.next()); // key
out.writeObject(it.getValue()); // value
}
}
/**
* Read the map in using a custom routine.
*/
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
in.defaultReadObject();
int count = in.readInt();
if (count > 3) {
delegateMap = createDelegateMap();
}
for (int i = count; i > 0; i--) {
put(in.readObject(), in.readObject());
}
}
//-----------------------------------------------------------------------
/**
* Clones the map without cloning the keys or values.
*
* @return a shallow clone
* @since Commons Collections 3.1
*/
public Object clone() {
try {
Flat3Map cloned = (Flat3Map) super.clone();
if (cloned.delegateMap != null) {
cloned.delegateMap = (HashedMap) cloned.delegateMap.clone();
}
return cloned;
} catch (CloneNotSupportedException ex) {
throw new InternalError();
}
}
/**
* Compares this map with another.
*
* @param obj the object to compare to
* @return true if equal
*/
public boolean equals(Object obj) {
if (obj == this) {
return true;
}
if (delegateMap != null) {
return delegateMap.equals(obj);
}
if (obj instanceof Map == false) {
return false;
}
Map other = (Map) obj;
if (size != other.size()) {
return false;
}
if (size > 0) {
Object otherValue = null;
switch (size) { // drop through
case 3:
if (other.containsKey(key3) == false) {
return false;
}
otherValue = other.get(key3);
if (value3 == null ? otherValue != null : !value3.equals(otherValue)) {
return false;
}
case 2:
if (other.containsKey(key2) == false) {
return false;
}
otherValue = other.get(key2);
if (value2 == null ? otherValue != null : !value2.equals(otherValue)) {
return false;
}
case 1:
if (other.containsKey(key1) == false) {
return false;
}
otherValue = other.get(key1);
if (value1 == null ? otherValue != null : !value1.equals(otherValue)) {
return false;
}
}
}
return true;
}
/**
* Gets the standard Map hashCode.
*
* @return the hash code defined in the Map interface
*/
public int hashCode() {
if (delegateMap != null) {
return delegateMap.hashCode();
}
int total = 0;
switch (size) { // drop through
case 3:
total += (hash3 ^ (value3 == null ? 0 : value3.hashCode()));
case 2:
total += (hash2 ^ (value2 == null ? 0 : value2.hashCode()));
case 1:
total += (hash1 ^ (value1 == null ? 0 : value1.hashCode()));
}
return total;
}
/**
* Gets the map as a String.
*
* @return a string version of the map
*/
public String toString() {
if (delegateMap != null) {
return delegateMap.toString();
}
if (size == 0) {
return "{}";
}
StringBuffer buf = new StringBuffer(128);
buf.append('{');
switch (size) { // drop through
case 3:
buf.append((key3 == this ? "(this Map)" : key3));
buf.append('=');
buf.append((value3 == this ? "(this Map)" : value3));
buf.append(',');
case 2:
buf.append((key2 == this ? "(this Map)" : key2));
buf.append('=');
buf.append((value2 == this ? "(this Map)" : value2));
buf.append(',');
case 1:
buf.append((key1 == this ? "(this Map)" : key1));
buf.append('=');
buf.append((value1 == this ? "(this Map)" : value1));
}
buf.append('}');
return buf.toString();
}
}