Mega Code Archive
Copy On Write Map
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/*
* 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.
*
*/
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
/**
* A thread-safe version of {@link Map} in which all operations that change the
* Map are implemented by making a new copy of the underlying Map.
*
* While the creation of a new Map can be expensive, this class is designed for
* cases in which the primary function is to read data from the Map, not to
* modify the Map. Therefore the operations that do not cause a change to this
* class happen quickly and concurrently.
*
* @author The Apache MINA Project (dev@mina.apache.org)
* @version $Rev$, $Date$
*/
public class CopyOnWriteMap<K, V> implements Map<K, V>, Cloneable {
private volatile Map<K, V> internalMap;
/**
* Creates a new instance of CopyOnWriteMap.
*
*/
public CopyOnWriteMap() {
internalMap = new HashMap<K, V>();
}
/**
* Creates a new instance of CopyOnWriteMap with the specified initial size
*
* @param initialCapacity
* The initial size of the Map.
*/
public CopyOnWriteMap(int initialCapacity) {
internalMap = new HashMap<K, V>(initialCapacity);
}
/**
* Creates a new instance of CopyOnWriteMap in which the
* initial data being held by this map is contained in
* the supplied map.
*
* @param data
* A Map containing the initial contents to be placed into
* this class.
*/
public CopyOnWriteMap(Map<K, V> data) {
internalMap = new HashMap<K, V>(data);
}
/**
* Adds the provided key and value to this map.
*
* @see java.util.Map#put(java.lang.Object, java.lang.Object)
*/
public V put(K key, V value) {
synchronized (this) {
Map<K, V> newMap = new HashMap<K, V>(internalMap);
V val = newMap.put(key, value);
internalMap = newMap;
return val;
}
}
/**
* Removed the value and key from this map based on the
* provided key.
*
* @see java.util.Map#remove(java.lang.Object)
*/
public V remove(Object key) {
synchronized (this) {
Map<K, V> newMap = new HashMap<K, V>(internalMap);
V val = newMap.remove(key);
internalMap = newMap;
return val;
}
}
/**
* Inserts all the keys and values contained in the
* provided map to this map.
*
* @see java.util.Map#putAll(java.util.Map)
*/
public void putAll(Map<? extends K, ? extends V> newData) {
synchronized (this) {
Map<K, V> newMap = new HashMap<K, V>(internalMap);
newMap.putAll(newData);
internalMap = newMap;
}
}
/**
* Removes all entries in this map.
*
* @see java.util.Map#clear()
*/
public void clear() {
synchronized (this) {
internalMap = new HashMap<K, V>();
}
}
//
// Below are methods that do not modify
// the internal Maps
/**
* Returns the number of key/value pairs in this map.
*
* @see java.util.Map#size()
*/
public int size() {
return internalMap.size();
}
/**
* Returns true if this map is empty, otherwise false.
*
* @see java.util.Map#isEmpty()
*/
public boolean isEmpty() {
return internalMap.isEmpty();
}
/**
* Returns true if this map contains the provided key, otherwise
* this method return false.
*
* @see java.util.Map#containsKey(java.lang.Object)
*/
public boolean containsKey(Object key) {
return internalMap.containsKey(key);
}
/**
* Returns true if this map contains the provided value, otherwise
* this method returns false.
*
* @see java.util.Map#containsValue(java.lang.Object)
*/
public boolean containsValue(Object value) {
return internalMap.containsValue(value);
}
/**
* Returns the value associated with the provided key from this
* map.
*
* @see java.util.Map#get(java.lang.Object)
*/
public V get(Object key) {
return internalMap.get(key);
}
/**
* This method will return a read-only {@link Set}.
*/
public Set<K> keySet() {
return internalMap.keySet();
}
/**
* This method will return a read-only {@link Collection}.
*/
public Collection<V> values() {
return internalMap.values();
}
/**
* This method will return a read-only {@link Set}.
*/
public Set<Entry<K, V>> entrySet() {
return internalMap.entrySet();
}
@Override
public Object clone() {
try {
return super.clone();
} catch (CloneNotSupportedException e) {
throw new InternalError();
}
}
}
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