Copy On Write Map : Customized Map « Collections Data Structure « Java

1. Java
2. Collections Data Structure
3. Customized Map

Copy On Write Map

    
/*
 *  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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