org.apache.commons.collections4.MultiValuedMap Maven / Gradle / Ivy
Show all versions of commons-collections4 Show documentation
/*
* 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.Collection;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
/**
* Defines a map that holds a collection of values against each key.
*
* A {@code MultiValuedMap} is a Map with slightly different semantics:
*
* - Putting a value into the map will add the value to a {@link Collection} at that key.
* - Getting a value will return a {@link Collection}, holding all the values put to that key.
*
*
* For example:
*
* MultiValuedMap<K, String> map = new MultiValuedHashMap<K, String>();
* map.put(key, "A");
* map.put(key, "B");
* map.put(key, "C");
* Collection<String> coll = map.get(key);
*
*
* coll will be a collection containing "A", "B", "C".
*
*
* @param the type of the keys in this map
* @param the type of the values in this map
* @since 4.1
*/
public interface MultiValuedMap {
// Query operations
/**
* Gets the total size of the map.
*
* Implementations would return the total size of the map which is the count
* of the values from all keys.
*
* @return the total size of the map
*/
int size();
/**
* Returns {@code true} if this map contains no key-value mappings.
*
* @return {@code true} if this map contains no key-value mappings
*/
boolean isEmpty();
/**
* Returns {@code true} if this map contains a mapping for the specified
* key. More formally, returns {@code true} if and only if this map contains
* a mapping for a key {@code k} such that {@code (key==null ? k==null : key.equals(k))}.
* (There can be at most one such mapping.)
*
* @param key key whose presence in this map is to be tested
* @return true if this map contains a mapping for the specified key
* @throws NullPointerException if the specified key is null and this map
* does not permit null keys (optional)
*/
boolean containsKey(Object key);
/**
* Checks whether the map contains at least one mapping for the specified value.
*
* @param value the value to search for
* @return true if the map contains the value
* @throws NullPointerException if the value is null and null values are not supported
* by the used collection types (optional)
*/
boolean containsValue(Object value);
/**
* Checks whether the map contains a mapping for the specified key and value.
*
* @param key the key to search for
* @param value the value to search for
* @return true if the map contains the value
*/
boolean containsMapping(Object key, Object value);
/**
* Returns a view collection of the values associated with the specified key.
*
* This method will return an empty collection if {@link #containsKey(Object)}
* returns {@code false}. Changes to the returned collection will update the underlying
* {@code MultiValuedMap} and vice-versa.
*
* @param key the key to retrieve
* @return the {@code Collection} of values, implementations should
* return an empty collection for no mapping
* @throws NullPointerException if the key is null and null keys are invalid (optional)
*/
Collection get(K key);
// Modification operations
/**
* Adds a key-value mapping to this multi-valued map.
*
* Unlike a normal {@code Map} the previous value is not replaced.
* Instead the new value is added to the collection stored against the key.
* Depending on the collection type used, duplicate key-value mappings may
* be allowed.
*
* The method will return {@code true} if the size of the multi-valued map
* has been increased because of this operation.
*
* @param key the key to store against
* @param value the value to add to the collection at the key
* @return true if the map changed as a result of this put operation, or false
* if the map already contained the key-value mapping and the collection
* type does not allow duplicate values, e.g. when using a Set
* @throws UnsupportedOperationException if the put operation is not supported by
* this multi-valued map, e.g. if it is unmodifiable
* @throws NullPointerException if the key or value is null and null is invalid (optional)
* @throws IllegalArgumentException if some aspect of the specified key or value prevents
* it from being stored in this multi-valued map
*/
boolean put(K key, V value);
/**
* Adds a mapping to the specified key for all values contained in the given Iterable.
*
* @param key the key to store against
* @param values the values to add to the collection at the key, may not be null
* @return true if the map changed as a result of this operation
* @throws NullPointerException if the specified iterable is null, or if this map
* does not permit null keys or values, and the specified key or values contain
* null (optional)
*/
boolean putAll(K key, Iterable values);
/**
* Copies all mappings from the specified map to this multi-valued map
* (optional operation).
*
* The effect of this call is equivalent to that of calling
* {@link #put(Object,Object) put(k, v)} on this map once for each mapping
* from key {@code k} to value {@code v} in the specified map.
*
* The behavior of this operation is undefined if the specified map is modified
* while the operation is in progress.
*
* @param map mappings to be stored in this map, may not be null
* @return true if the map changed as a result of this operation
* @throws UnsupportedOperationException if the {@code putAll} operation is
* not supported by this map
* @throws NullPointerException if the specified map is null, or if this map
* does not permit null keys or values, and the specified map
* contains null keys or values (optional)
* @throws IllegalArgumentException if some property of a key or value in
* the specified map prevents it from being stored in this map
*/
boolean putAll(Map map);
/**
* Copies all mappings from the specified map to this multi-valued map
* (optional operation).
*
* The effect of this call is equivalent to that of calling
* {@link #put(Object,Object) put(k, v)} on this map once for each
* mapping from key {@code k} to value {@code v} in the specified map.
*
* The behavior of this operation is undefined if the specified map is modified
* while the operation is in progress.
*
* @param map mappings to be stored in this map, may not be null
* @return true if the map changed as a result of this operation
* @throws UnsupportedOperationException if the {@code putAll} operation is
* not supported by this map
* @throws NullPointerException if the specified map is null, or if this map
* does not permit null keys or values, and the specified map
* contains null keys or values (optional)
* @throws IllegalArgumentException if some property of a key or value in
* the specified map prevents it from being stored in this map
*/
boolean putAll(MultiValuedMap map);
/**
* Removes all values associated with the specified key.
*
* The returned collection may be modifiable, but updates will not be propagated
* to this multi-valued map. In case no mapping was stored for the specified
* key, an empty, unmodifiable collection will be returned.
*
* @param key the key to remove values from
* @return the values that were removed
* @throws UnsupportedOperationException if the map is unmodifiable
* @throws NullPointerException if the key is null and null keys are invalid (optional)
*/
Collection remove(Object key);
/**
* Removes a key-value mapping from the map.
*
* The item is removed from the collection mapped to the specified key.
* Other values attached to that key are unaffected.
*
* If the last value for a key is removed, implementations typically return
* an empty collection from a subsequent get(Object).
*
* @param key the key to remove from
* @param item the item to remove
* @return true if the mapping was removed, false otherwise
* @throws UnsupportedOperationException if the map is unmodifiable
* @throws NullPointerException if the key or value is null and null is invalid (optional)
*/
boolean removeMapping(Object key, Object item);
/**
* Removes all of the mappings from this map (optional operation).
*
* The map will be empty after this call returns.
*
* @throws UnsupportedOperationException if the map is unmodifiable
*/
void clear();
// Views
/**
* Returns a {@link Collection} view of the mappings contained in this multi-valued map.
*
* The collection is backed by the map, so changes to the map are reflected
* in the collection, and vice-versa.
*
* @return a set view of the mappings contained in this map
*/
Collection> entries();
/**
* Returns a {@link MultiSet} view of the keys contained in this multi-valued map.
*
* The {@link MultiSet#getCount(Object)} method of the returned multiset will give
* the same result a calling {@code get(Object).size()} for the same key.
*
* This multiset is backed by the map, so any changes in the map are reflected in
* the multiset.
*
* @return a multiset view of the keys contained in this map
*/
MultiSet keys();
/**
* Returns a {@link Set} view of the keys contained in this multi-valued map.
*
* The set is backed by the map, so changes to the map are reflected
* in the set, and vice-versa.
*
* If the map is modified while an iteration over the set is in
* progress (except through the iterator's own {@code remove} operation),
* the result of the iteration is undefined. The set supports element
* removal, which removes the corresponding mapping from the map, via the
* {@code Iterator.remove}, {@code Set.remove}, {@code removeAll},
* {@code retainAll}, and {@code clear} operations. It does not support
* the {@code add} or {@code addAll} operations.
*
* @return a set view of the keys contained in this map
*/
Set keySet();
/**
* Gets a {@link Collection} view of all values contained in this multi-valued map.
*
* Implementations typically return a collection containing the combination
* of values from all keys.
*
* @return a collection view of the values contained in this multi-valued map
*/
Collection values();
/**
* Returns a view of this multi-valued map as a {@code Map} from each distinct
* key to the non-empty collection of that key's associated values.
*
* Note that {@code this.asMap().get(k)} is equivalent to {@code this.get(k)}
* only when {@code k} is a key contained in the multi-valued map; otherwise it
* returns {@code null} as opposed to an empty collection.
*
* Changes to the returned map or the collections that serve as its values
* will update the underlying multi-valued map, and vice versa. The map does
* not support {@code put} or {@code putAll}, nor do its entries support
* {@link java.util.Map.Entry#setValue(Object) setValue}.
*
* @return a map view of the mappings in this multi-valued map
*/
Map> asMap();
// Iterators
/**
* Obtains a MapIterator over this multi-valued map.
*
* A map iterator is an efficient way of iterating over maps. There is no
* need to access the entries collection or use {@code Map.Entry} objects.
*
* @return a map iterator
*/
MapIterator mapIterator();
}