/*
 * 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.
 A ListValuedMap is a Map with slightly different semantics: 

  
Putting a value into the map will add the value to a List at that key.
  
Getting a value will return a List, holding all the values put to that key.

Type parameters:
<K> – the type of the keys in this map
<V> – the type of the values in this map
Since:
4.1/**
 * 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.

This method will return an empty list if MultiValuedMap.containsKey(Object) returns false. Changes to the returned list will update the underlying ListValuedMap and vice-versa. 
Params:
key –  the key to retrieve
Throws:
NullPointerException – if the key is null and null keys are invalid
Returns:
the List of values, implementations should return an empty List for no mapping/**
     * 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.

The returned list may 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.
Params:
key –  the key to remove values from
Throws:
UnsupportedOperationException – if the map is unmodifiable
NullPointerException – if the key is null and null keys are invalid
Returns:
the List of values removed, implementations typically return an empty, unmodifiable List for no mapping found/**
     * 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);

}