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.Set;
020
021/**
022 * Defines a map that holds a set of values against each key.
023 * <p>
024 * A {@code SetValuedMap} is a Map with slightly different semantics:
025 * <ul>
026 *   <li>Putting a value into the map will add the value to a {@link Set} at that key.</li>
027 *   <li>Getting a value will return a {@link Set}, 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 SetValuedMap<K, V> extends MultiValuedMap<K, V> {
035
036    /**
037     * Gets the set of values associated with the specified key.
038     * <p>
039     * Implementations typically return an empty {@code Set} if no values
040     * have been mapped to the key.
041     * <p>
042     *
043     * @param key  the key to retrieve
044     * @return the {@code Set} of values, implementations should return an
045     *   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 <i>may</i> be modifiable, but updates will not be
055     * propagated to this set-valued map. In case no mapping was stored for the
056     * specified key, an empty, unmodifiable set will be returned.
057     *
058     * @param key  the key to remove values from
059     * @return the {@code Set} of values removed, implementations should
060     *   return null for no mapping found, but may return an empty collection
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    Set<V> remove(Object key);
066}