/*

 * Licensed to the Apache Software Foundation (ASF) under one or more

 * contributor license agreements.  See the NOTICE file distributed with

 * this work for additional information regarding copyright ownership.

 * The ASF licenses this file to You under the Apache License, Version 2.0

 * (the "License"); you may not use this file except in compliance with

 * the License.  You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package org.apache.commons.collections4;

import java.util.List;

/**

 * Defines a map that holds a list of values against each key.

 * <p>

 * A {@code ListValuedMap} is a Map with slightly different semantics:

 * </p>

 * <ul>

 *   <li>Putting a value into the map will add the value to a {@link List} at that key.</li>

 *   <li>Getting a value will return a {@link List}, holding all the values put to that key.</li>

 * </ul>

 *

 * @param <K> the type of the keys in this map

 * @param <V> the type of the values in this map

 * @since 4.1

 */

public interface ListValuedMap<K, V> extends MultiValuedMap<K, V> {

    /**

     * Gets the list of values associated with the specified key.

     * <p>

     * This method will return an <b>empty</b> list if

     * {@link #containsKey(Object)} returns {@code false}. Changes to the

     * returned list will update the underlying {@code ListValuedMap} and

     * vice-versa.

     *

     * @param key  the key to retrieve

     * @return the {@code List} of values, implementations should return an

     *   empty {@code List} for no mapping

     * @throws NullPointerException if the key is null and null keys are invalid

     */

    @Override

    List<V> get(K key);

    /**

     * Removes all values associated with the specified key.

     * <p>

     * The returned list <i>may</i> be modifiable, but updates will not be

     * propagated to this list-valued map. In case no mapping was stored for the

     * specified key, an empty, unmodifiable list will be returned.

     *

     * @param key  the key to remove values from

     * @return the {@code List} of values removed, implementations

     *   typically return an empty, unmodifiable {@code List} for no mapping found

     * @throws UnsupportedOperationException if the map is unmodifiable

     * @throws NullPointerException if the key is null and null keys are invalid

     */

    @Override

    List<V> remove(Object key);

}