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Commons Collections example source code file (MultiMap.java)

This example Commons Collections source code file (MultiMap.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

collection, collection, map, map, multimap, multimap, object, object, util

The Commons Collections MultiMap.java source code

/*
 *  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;

import java.util.Collection;
import java.util.Map;

/** 
 * Defines a map that holds a collection of values against each key.
 * <p>
 * A <code>MultiMap is a Map with slightly different semantics.
 * Putting a value into the map will add the value to a Collection at that key.
 * Getting a value will return a Collection, holding all the values put to that key.
 * <p>
 * For example:
 * <pre>
 * MultiMap mhm = new MultiHashMap();
 * mhm.put(key, "A");
 * mhm.put(key, "B");
 * mhm.put(key, "C");
 * Collection coll = (Collection) mhm.get(key);</pre>
 * <p>
 * <code>coll will be a collection containing "A", "B", "C".
 * <p>
 * NOTE: Additional methods were added to this interface in Commons Collections 3.1.
 * These were added solely for documentation purposes and do not change the interface
 * as they were defined in the superinterface <code>Map anyway.
 *
 * @since Commons Collections 2.0
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 * 
 * @author Christopher Berry
 * @author James Strachan
 * @author Stephen Colebourne
 */
public interface MultiMap extends Map {

    /**
     * Removes a specific value from map.
     * <p>
     * The item is removed from the collection mapped to the specified key.
     * Other values attached to that key are unaffected.
     * <p>
     * If the last value for a key is removed, implementations typically
     * return <code>null from a subsequant get(Object), however
     * they may choose to return an empty collection.
     * 
     * @param key  the key to remove from
     * @param item  the item to remove
     * @return the value removed (which was passed in), null if nothing removed
     * @throws UnsupportedOperationException if the map is unmodifiable
     * @throws ClassCastException if the key or value is of an invalid type
     * @throws NullPointerException if the key or value is null and null is invalid
     */
    public Object remove(Object key, Object item);

    //-----------------------------------------------------------------------
    /**
     * Gets the number of keys in this map.
     * <p>
     * Implementations typically return only the count of keys in the map
     * This cannot be mandated due to backwards compatability of this interface.
     *
     * @return the number of key-collection mappings in this map
     */
    int size();

    /**
     * Gets the collection of values associated with the specified key.
     * <p>
     * The returned value will implement <code>Collection. Implementations
     * are free to declare that they return <code>Collection subclasses
     * such as <code>List or Set.
     * <p>
     * Implementations typically return <code>null if no values have
     * been mapped to the key, however the implementation may choose to
     * return an empty collection.
     * <p>
     * Implementations may choose to return a clone of the internal collection.
     *
     * @param key  the key to retrieve
     * @return the <code>Collection of values, implementations should
     *  return <code>null for no mapping, but may return an empty collection
     * @throws ClassCastException if the key is of an invalid type
     * @throws NullPointerException if the key is null and null keys are invalid
     */
    Object get(Object key);

    /**
     * Checks whether the map contains the value specified.
     * <p>
     * Implementations typically check all collections against all keys for the value.
     * This cannot be mandated due to backwards compatability of this interface.
     *
     * @param value  the value to search for
     * @return true if the map contains the value
     * @throws ClassCastException if the value is of an invalid type
     * @throws NullPointerException if the value is null and null value are invalid
     */
    boolean containsValue(Object value);

    /**
     * Adds the value to the collection associated with the specified key.
     * <p>
     * Unlike a normal <code>Map the previous value is not replaced.
     * Instead the new value is added to the collection stored against the key.
     * The collection may be a <code>List, Set or other
     * collection dependent on implementation.
     *
     * @param key  the key to store against
     * @param value  the value to add to the collection at the key
     * @return typically the value added if the map changed and null if the map did not change
     * @throws UnsupportedOperationException if the map is unmodifiable
     * @throws ClassCastException if the key or value is of an invalid type
     * @throws NullPointerException if the key or value is null and null is invalid
     * @throws IllegalArgumentException if the key or value is invalid
     */
    Object put(Object key, Object value);

    /**
     * Removes all values associated with the specified key.
     * <p>
     * Implementations typically return <code>null from a subsequant
     * <code>get(Object), however they may choose to return an empty collection.
     *
     * @param key  the key to remove values from
     * @return the <code>Collection of values removed, implementations should
     *  return <code>null for no mapping found, but may return an empty collection
     * @throws UnsupportedOperationException if the map is unmodifiable
     * @throws ClassCastException if the key is of an invalid type
     * @throws NullPointerException if the key is null and null keys are invalid
     */
    Object remove(Object key);

    /**
     * Gets a collection containing all the values in the map.
     * <p>
     * Inplementations typically return a collection containing the combination
     * of values from all keys.
     * This cannot be mandated due to backwards compatability of this interface.
     *
     * @return a collection view of the values contained in this map
     */
    Collection values();

}

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