multikeymap.java

初级java程序员如果想要更深一步提高自己的实力

/*
 *  Copyright 2004 The Apache Software Foundation
 *
 *  Licensed 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.Serializable;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import org.apache.commons.collections.IterableMap;
import org.apache.commons.collections.MapIterator;
import org.apache.commons.collections.keyvalue.MultiKey;

/**
 * A <code>Map</code> implementation that uses multiple keys to map the value.
 * <p>
 * This class is the most efficient way to uses multiple keys to map to a value.
 * The best way to use this class is via the additional map-style methods.
 * These provide <code>get</code>, <code>containsKey</code>, <code>put</code> and
 * <code>remove</code> for individual keys which operate without extra object creation.
 * <p>
 * The additional methods are the main interface of this map.
 * As such, you will not normally hold this map in a variable of type <code>Map</code>.
 * <p>
 * The normal map methods take in and return a {@link MultiKey}.
 * If you try to use <code>put()</code> with any other object type a
 * <code>ClassCastException</code> is thrown. If you try to use <code>null</code> as
 * the key in <code>put()</code> a <code>NullPointerException</code> is thrown.
 * <p>
 * This map is implemented as a decorator of a <code>AbstractHashedMap</code> which
 * enables extra behaviour to be added easily.
 * <ul>
 * <li><code>MultiKeyMap.decorate(new LinkedMap())</code> creates an ordered map.
 * <li><code>MultiKeyMap.decorate(new LRUMap())</code> creates an least recently used map.
 * <li><code>MultiKeyMap.decorate(new ReferenceMap())</code> creates a garbage collector sensitive map.
 * </ul>
 * Note that <code>IdentityMap</code> and <code>ReferenceIdentityMap</code> are unsuitable
 * for use as the key comparison would work on the whole MultiKey, not the elements within.
 * <p>
 * As an example, consider a least recently used cache that uses a String airline code
 * and a Locale to lookup the airline's name:
 * <pre>
 * private MultiKeyMap cache = MultiKeyMap.decorate(new LRUMap(50));
 * 
 * public String getAirlineName(String code, String locale) {
 *   String name = (String) cache.get(code, locale);
 *   if (name == null) {
 *     name = getAirlineNameFromDB(code, locale);
 *     cache.put(code, locale, name);
 *   }
 *   return name;
 * }
 * </pre>
 * <p>
 * <strong>Note that MultiKeyMap is not synchronized and is not thread-safe.</strong>
 * If you wish to use this map from multiple threads concurrently, you must use
 * appropriate synchronization. This class may throw exceptions when accessed
 * by concurrent threads without synchronization.
 *
 * @since Commons Collections 3.1
 * @version $Revision: 348007 $ $Date: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $
 *
 * @author Stephen Colebourne
 */
public class MultiKeyMap
        implements IterableMap, Serializable {

    /** Serialisation version */
    private static final long serialVersionUID = -1788199231038721040L;

    /** The decorated map */
    protected final AbstractHashedMap map;

    //-----------------------------------------------------------------------
    /**
     * Decorates the specified map to add the MultiKeyMap API and fast query.
     * The map must not be null and must be empty.
     *
     * @param map  the map to decorate, not null
     * @throws IllegalArgumentException if the map is null or not empty
     */
    public static MultiKeyMap decorate(AbstractHashedMap map) {
        if (map == null) {
            throw new IllegalArgumentException("Map must not be null");
        }
        if (map.size() > 0) {
            throw new IllegalArgumentException("Map must be empty");
        }
        return new MultiKeyMap(map);
    }

    //-----------------------------------------------------------------------    
    /**
     * Constructs a new MultiKeyMap that decorates a <code>HashedMap</code>.
     */
    public MultiKeyMap() {
        super();
        map = new HashedMap();
    }

    /**
     * Constructor that decorates the specified map and is called from
     * {@link #decorate(AbstractHashedMap)}.
     * The map must not be null and should be empty or only contain valid keys.
     * This constructor performs no validation.
     *
     * @param map  the map to decorate
     */
    protected MultiKeyMap(AbstractHashedMap map) {
        super();
        this.map = map;
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the value mapped to the specified multi-key.
     * 
     * @param key1  the first key
     * @param key2  the second key
     * @return the mapped value, null if no match
     */
    public Object get(Object key1, Object key2) {
        int hashCode = hash(key1, key2);
        AbstractHashedMap.HashEntry entry = map.data[map.hashIndex(hashCode, map.data.length)];
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2)) {
                return entry.getValue();
            }
            entry = entry.next;
        }
        return null;
    }

    /**
     * Checks whether the map contains the specified multi-key.
     * 
     * @param key1  the first key
     * @param key2  the second key
     * @return true if the map contains the key
     */
    public boolean containsKey(Object key1, Object key2) {
        int hashCode = hash(key1, key2);
        AbstractHashedMap.HashEntry entry = map.data[map.hashIndex(hashCode, map.data.length)];
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2)) {
                return true;
            }
            entry = entry.next;
        }
        return false;
    }

    /**
     * Stores the value against the specified multi-key.
     * 
     * @param key1  the first key
     * @param key2  the second key
     * @param value  the value to store
     * @return the value previously mapped to this combined key, null if none
     */
    public Object put(Object key1, Object key2, Object value) {
        int hashCode = hash(key1, key2);
        int index = map.hashIndex(hashCode, map.data.length);
        AbstractHashedMap.HashEntry entry = map.data[index];
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2)) {
                Object oldValue = entry.getValue();
                map.updateEntry(entry, value);
                return oldValue;
            }
            entry = entry.next;
        }
        
        map.addMapping(index, hashCode, new MultiKey(key1, key2), value);
        return null;
    }

    /**
     * Removes the specified multi-key from this map.
     * 
     * @param key1  the first key
     * @param key2  the second key
     * @return the value mapped to the removed key, null if key not in map
     */
    public Object remove(Object key1, Object key2) {
        int hashCode = hash(key1, key2);
        int index = map.hashIndex(hashCode, map.data.length);
        AbstractHashedMap.HashEntry entry = map.data[index];
        AbstractHashedMap.HashEntry previous = null;
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2)) {
                Object oldValue = entry.getValue();
                map.removeMapping(entry, index, previous);
                return oldValue;
            }
            previous = entry;
            entry = entry.next;
        }
        return null;
    }

    /**
     * Gets the hash code for the specified multi-key.
     * 
     * @param key1  the first key
     * @param key2  the second key
     * @return the hash code
     */
    protected int hash(Object key1, Object key2) {
        int h = 0;
        if (key1 != null) {
            h ^= key1.hashCode();
        }
        if (key2 != null) {
            h ^= key2.hashCode();
        }
        h += ~(h << 9);
        h ^=  (h >>> 14);
        h +=  (h << 4);
        h ^=  (h >>> 10);
        return h;
    }

    /**
     * Is the key equal to the combined key.
     * 
     * @param entry  the entry to compare to
     * @param key1  the first key
     * @param key2  the second key
     * @return true if the key matches
     */
    protected boolean isEqualKey(AbstractHashedMap.HashEntry entry, Object key1, Object key2) {
        MultiKey multi = (MultiKey) entry.getKey();
        return
            multi.size() == 2 &&
            (key1 == null ? multi.getKey(0) == null : key1.equals(multi.getKey(0))) &&
            (key2 == null ? multi.getKey(1) == null : key2.equals(multi.getKey(1)));
    }

    //-----------------------------------------------------------------------
    /**
     * Gets the value mapped to the specified multi-key.
     * 
     * @param key1  the first key
     * @param key2  the second key
     * @param key3  the third key
     * @return the mapped value, null if no match
     */
    public Object get(Object key1, Object key2, Object key3) {
        int hashCode = hash(key1, key2, key3);
        AbstractHashedMap.HashEntry entry = map.data[map.hashIndex(hashCode, map.data.length)];
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3)) {
                return entry.getValue();
            }
            entry = entry.next;
        }
        return null;
    }

    /**
     * Checks whether the map contains the specified multi-key.
     * 
     * @param key1  the first key
     * @param key2  the second key
     * @param key3  the third key
     * @return true if the map contains the key
     */
    public boolean containsKey(Object key1, Object key2, Object key3) {
        int hashCode = hash(key1, key2, key3);
        AbstractHashedMap.HashEntry entry = map.data[map.hashIndex(hashCode, map.data.length)];
        while (entry != null) {
            if (entry.hashCode == hashCode && isEqualKey(entry, key1, key2, key3)) {
                return true;
            }
            entry = entry.next;
        }
        return false;
    }

    /**
     * Stores the value against the specified multi-key.
     * 
     * @param key1  the first key
     * @param key2  the second key
     * @param key3  the third key
     * @param value  the value to store
     * @return the value previously mapped to this combined key, null if none
     */
    public Object put(Object key1, Object key2, Object key3, Object value) {
        int hashCode = hash(key1, key2, key3);