    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}