Java tutorial
/* * 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. * <p> * A {@code SetValuedMap} is a Map with slightly different semantics: * <ul> * <li>Putting a value into the map will add the value to a {@link Set} at that key.</li> * <li>Getting a value will return a {@link Set}, holding all the values put to that key.</li> * </ul> * * @since 4.1 * @version $Id: SetValuedMap.java 1685299 2015-06-13 18:27:11Z tn $ */ public interface SetValuedMap<K, V> extends MultiValuedMap<K, V> { /** * Gets the set of values associated with the specified key. * <p> * Implementations typically return an empty {@code Set} if no values * have been mapped to the key. * <p> * * @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<V> get(K key); /** * Removes all values associated with the specified key. * <p> * The returned set <i>may</i> 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<V> remove(Object key); }