org.apache.commons.collections4.SetValuedMap Maven / Gradle / Ivy
/*
* 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.Set;
/**
* Defines a map that holds a set of values against each key.
*
* A {@code SetValuedMap} is a Map with slightly different semantics:
*
* - Putting a value into the map will add the value to a {@link Set} at that key.
* - Getting a value will return a {@link Set}, holding all the values put to that key.
*
*
* @param the type of the keys in this map
* @param the type of the values in this map
* @since 4.1
*/
public interface SetValuedMap extends MultiValuedMap {
/**
* Gets the set of values associated with the specified key.
*
* Implementations typically return an empty {@code Set} if no values
* have been mapped to the key.
*
*
* @param key the key to retrieve
* @return the {@code Set} of values, implementations should return an
* empty {@code Set} for no mapping
* @throws NullPointerException if the key is null and null keys are invalid
*/
@Override
Set get(K key);
/**
* Removes all values associated with the specified key.
*
* The returned set may be modifiable, but updates will not be
* propagated to this set-valued map. In case no mapping was stored for the
* specified key, an empty, unmodifiable set will be returned.
*
* @param key the key to remove values from
* @return the {@code Set} of values removed, implementations should
* return null for no mapping found, but may return an empty collection
* @throws UnsupportedOperationException if the map is unmodifiable
* @throws NullPointerException if the key is null and null keys are invalid
*/
@Override
Set remove(Object key);
}