    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}