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 *      https://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 */
017
018package org.apache.commons.collections4;
019
020import java.util.List;
021
022/**
023 * Defines a map that holds a list of values against each key.
024 * <p>
025 * A {@code ListValuedMap} is a Map with slightly different semantics:
026 * </p>
027 * <ul>
028 * <li>Putting a value into the map will add the value to a {@link List} at that key.</li>
029 * <li>Getting a value will return a {@link List}, holding all the values put to that key.</li>
030 * </ul>
031 *
032 * @param <K> The type of the keys in this map
033 * @param <V> The type of the values in this map
034 * @since 4.1
035 */
036public interface ListValuedMap<K, V> extends MultiValuedMap<K, V> {
037
038    /**
039     * Gets the list of values associated with the specified key.
040     * <p>
041     * This method will return an <strong>empty</strong> list if {@link #containsKey(Object)} returns {@code false}. Changes to the returned list will update
042     * the underlying {@code ListValuedMap} and vice-versa.
043     * </p>
044     *
045     * @param key The key to retrieve.
046     * @return The {@code List} of values, implementations should return an 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 <em>may</em> be modifiable, but updates will not be propagated to this list-valued map. In case no mapping was stored for the specified
056     * key, an empty, unmodifiable list will be returned.
057     * </p>
058     *
059     * @param key The key to remove values from.
060     * @return The {@code List} of values removed, implementations typically return an empty, unmodifiable {@code List} for no mapping found.
061     * @throws UnsupportedOperationException if the map is unmodifiable.
062     * @throws NullPointerException          if the key is null and null keys are invalid.
063     */
064    @Override
065    List<V> remove(Object key);
066}