    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.Set;
    021
    022/**
    023 * Defines a map that holds a set of values against each key.
    024 * <p>
    025 * A {@code SetValuedMap} 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 Set} at that key.</li>
    029 * <li>Getting a value will return a {@link Set}, 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 SetValuedMap<K, V> extends MultiValuedMap<K, V> {
    037
    038    /**
    039     * Gets the set of values associated with the specified key.
    040     * <p>
    041     * Implementations typically return an empty {@code Set} if no values have been mapped to the key.
    042     * </p>
    043     *
    044     * @param key The key to retrieve.
    045     * @return The {@code Set} of values, implementations should return an empty {@code Set} for no mapping.
    046     * @throws NullPointerException if the key is null and null keys are invalid.
    047     */
    048    @Override
    049    Set<V> get(K key);
    050
    051    /**
    052     * Removes all values associated with the specified key.
    053     * <p>
    054     * The returned set <em>may</em> be modifiable, but updates will not be propagated to this set-valued map. In case no mapping was stored for the specified
    055     * key, an empty, unmodifiable set will be returned.
    056     * </p>
    057     *
    058     * @param key The key to remove values from.
    059     * @return The {@code Set} of values removed, implementations should return null for no mapping found, but may return an empty collection.
    060     * @throws UnsupportedOperationException if the map is unmodifiable.
    061     * @throws NullPointerException          if the key is null and null keys are invalid.
    062     */
    063    @Override
    064    Set<V> remove(Object key);
    065}