org.apache.commons.collections.MultiMap Maven / Gradle / Ivy

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package org.apache.commons.collections;

import java.util.Map;

/** 
 * Defines a map that holds a collection of values against each key.
 * 
 * A 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 always return a Collection, holding all the
 * values put to that key. This implementation uses an ArrayList as the 
 * collection.
 * 

 * For example:
 * 
 * MultiMap mhm = new MultiHashMap();
 * mhm.put(key, "A");
 * mhm.put(key, "B");
 * mhm.put(key, "C");
 * Collection coll = (Collection) mhm.get(key);
 * 
 * coll will be a list containing "A", "B", "C".
 *
 * @since Commons Collections 2.0
 * @version $Revision: 1.10 $ $Date: 2004/01/14 21:43:04 $
 * 
 * @author Christopher Berry
 * @author James Strachan
 * @author Stephen Colebourne
 */
public interface MultiMap extends Map {
    
    /**
     * Removes a specific value from map.
     * 
     * The item is removed from the collection mapped to the specified key.
     * 
     * @param key  the key to remove from
     * @param item  the item to remove
     * @return the value removed (which was passed in)
     */
    public Object remove(Object key, Object item);
   
}