# ListMap.java

    /*
     * Copyright (c) 2008, Rickard Öberg. All Rights Reserved.
     *
     * 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.qi4j.api.util;

    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.List;

    /**
     * Map whose values are Lists of things. Create
     * one ArrayList for each key that is added. The list does not allow
     * duplicates.
     */
    public final class ListMap<K, V>
        extends HashMap<K, List<V>>
    {
        public void add( K key, V value )
        {
            List<V> list = get( key );
            if( list == null )
            {
                list = new ArrayList<V>();
                put( key, list );
            }
            if( !list.contains( value ) )
            {
                list.add( value );
            }
        }
    }