001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4;
018
019import java.util.List;
020
021/**
022 * Defines a map that holds a list of values against each key.
023 * <p>
024 * A {@code ListValuedMap} is a Map with slightly different semantics:
025 * <ul>
026 *   <li>Putting a value into the map will add the value to a {@link List} at that key.</li>
027 *   <li>Getting a value will return a {@link List}, holding all the values put to that key.</li>
028 * </ul>
029 *
030 * @param <K> the type of the keys in this map
031 * @param <V> the type of the values in this map
032 * @since 4.1
033 */
034public interface ListValuedMap<K, V> extends MultiValuedMap<K, V> {
035
036    /**
037     * Gets the list of values associated with the specified key.
038     * <p>
039     * This method will return an <b>empty</b> list if
040     * {@link #containsKey(Object)} returns {@code false}. Changes to the
041     * returned list will update the underlying {@code ListValuedMap} and
042     * vice-versa.
043     *
044     * @param key  the key to retrieve
045     * @return the {@code List} of values, implementations should return an
046     *   empty {@code List} for no mapping
047     * @throws NullPointerException if the key is null and null keys are invalid
048     */
049    @Override
050    List<V> get(K key);
051
052    /**
053     * Removes all values associated with the specified key.
054     * <p>
055     * The returned list <i>may</i> be modifiable, but updates will not be
056     * propagated to this list-valued map. In case no mapping was stored for the
057     * specified key, an empty, unmodifiable list will be returned.
058     *
059     * @param key  the key to remove values from
060     * @return the {@code List} of values removed, implementations
061     *   typically return an empty, unmodifiable {@code List} for no mapping found
062     * @throws UnsupportedOperationException if the map is unmodifiable
063     * @throws NullPointerException if the key is null and null keys are invalid
064     */
065    @Override
066    List<V> remove(Object key);
067
068}