eaglercraft-1.8/sources/main/java/com/google/common/collect/Multimap.java

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/*
* Copyright (C) 2007 The Guava Authors
*
* Licensed 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 com.google.common.collect;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Set;
import javax.annotation.Nullable;
import com.google.common.annotations.GwtCompatible;
/**
* A collection that maps keys to values, similar to {@link Map}, but in which
* each key may be associated with <i>multiple</i> values. You can visualize the
* contents of a multimap either as a map from keys to <i>nonempty</i>
* collections of values:
*
* <ul>
* <li>a 1, 2
* <li>b 3
* </ul>
*
* ... or as a single "flattened" collection of key-value pairs:
*
* <ul>
* <li>a 1
* <li>a 2
* <li>b 3
* </ul>
*
* <p>
* <b>Important:</b> although the first interpretation resembles how most
* multimaps are <i>implemented</i>, the design of the {@code Multimap} API is
* based on the <i>second</i> form. So, using the multimap shown above as an
* example, the {@link #size} is {@code 3}, not {@code 2}, and the
* {@link #values} collection is {@code [1, 2, 3]}, not {@code [[1, 2], [3]]}.
* For those times when the first style is more useful, use the multimap's
* {@link #asMap} view (or create a {@code Map<K, Collection<V>>} in the first
* place).
*
* <h3>Example</h3>
*
* <p>
* The following code:
*
* <pre>
* {
* &#64;code
*
* ListMultimap<String, String> multimap = ArrayListMultimap.create();
* for (President pres : US_PRESIDENTS_IN_ORDER) {
* multimap.put(pres.firstName(), pres.lastName());
* }
* for (String firstName : multimap.keySet()) {
* List<String> lastNames = multimap.get(firstName);
* out.println(firstName + ": " + lastNames);
* }
* }
* </pre>
*
* ... produces output such as:
*
* <pre>
* {@code
*
* Zachary: [Taylor]
* John: [Adams, Adams, Tyler, Kennedy] // Remember, Quincy!
* George: [Washington, Bush, Bush]
* Grover: [Cleveland, Cleveland] // Two, non-consecutive terms, rep'ing NJ!
* ...}
* </pre>
*
* <h3>Views</h3>
*
* <p>
* Much of the power of the multimap API comes from the <i>view collections</i>
* it provides. These always reflect the latest state of the multimap itself.
* When they support modification, the changes are <i>write-through</i> (they
* automatically update the backing multimap). These view collections are:
*
* <ul>
* <li>{@link #asMap}, mentioned above</li>
* <li>{@link #keys}, {@link #keySet}, {@link #values}, {@link #entries}, which
* are similar to the corresponding view collections of {@link Map}
* <li>and, notably, even the collection returned by {@link #get get(key)} is an
* active view of the values corresponding to {@code key}
* </ul>
*
* <p>
* The collections returned by the {@link #replaceValues replaceValues} and
* {@link #removeAll removeAll} methods, which contain values that have just
* been removed from the multimap, are naturally <i>not</i> views.
*
* <h3>Subinterfaces</h3>
*
* <p>
* Instead of using the {@code Multimap} interface directly, prefer the
* subinterfaces {@link ListMultimap} and {@link SetMultimap}. These take their
* names from the fact that the collections they return from {@code get} behave
* like (and, of course, implement) {@link List} and {@link Set}, respectively.
*
* <p>
* For example, the "presidents" code snippet above used a {@code
* ListMultimap}; if it had used a {@code SetMultimap} instead, two presidents
* would have vanished, and last names might or might not appear in
* chronological order.
*
* <p>
* <b>Warning:</b> instances of type {@code Multimap} may not implement
* {@link Object#equals} in the way you expect (multimaps containing the same
* key-value pairs, even in the same order, may or may not be equal). The
* recommended subinterfaces provide a much stronger guarantee.
*
* <h3>Comparison to a map of collections</h3>
*
* <p>
* Multimaps are commonly used in places where a {@code Map<K,
* Collection<V>>} would otherwise have appeared. The differences include:
*
* <ul>
* <li>There is no need to populate an empty collection before adding an entry
* with {@link #put put}.
* <li>{@code get} never returns {@code null}, only an empty collection.
* <li>A key is contained in the multimap if and only if it maps to at least one
* value. Any operation that causes a key to have zero associated values has the
* effect of <i>removing</i> that key from the multimap.
* <li>The total entry count is available as {@link #size}.
* <li>Many complex operations become easier; for example, {@code
* Collections.min(multimap.values())} finds the smallest value across all
* keys.
* </ul>
*
* <h3>Implementations</h3>
*
* <p>
* As always, prefer the immutable implementations,
* {@link ImmutableListMultimap} and {@link ImmutableSetMultimap}.
* General-purpose mutable implementations are listed above under "All Known
* Implementing Classes". You can also create a <i>custom</i> multimap, backed
* by any {@code
* Map} and {@link Collection} types, using the {@link Multimaps#newMultimap
* Multimaps.newMultimap} family of methods. Finally, another popular way to
* obtain a multimap is using {@link Multimaps#index Multimaps.index}. See the
* {@link Multimaps} class for these and other static utilities related to
* multimaps.
*
* <h3>Other Notes</h3>
*
* <p>
* As with {@code Map}, the behavior of a {@code Multimap} is not specified if
* key objects already present in the multimap change in a manner that affects
* {@code equals} comparisons. Use caution if mutable objects are used as keys
* in a {@code Multimap}.
*
* <p>
* All methods that modify the multimap are optional. The view collections
* returned by the multimap may or may not be modifiable. Any modification
* method that is not supported will throw
* {@link UnsupportedOperationException}.
*
* <p>
* See the Guava User Guide article on <a href=
* "http://code.google.com/p/guava-libraries/wiki/NewCollectionTypesExplained#Multimap">
* {@code Multimap}</a>.
*
* @author Jared Levy
* @since 2.0 (imported from Google Collections Library)
*/
@GwtCompatible
public interface Multimap<K, V> {
// Query Operations
/**
* Returns the number of key-value pairs in this multimap.
*
* <p>
* <b>Note:</b> this method does not return the number of <i>distinct keys</i>
* in the multimap, which is given by {@code keySet().size()} or
* {@code asMap().size()}. See the opening section of the {@link Multimap} class
* documentation for clarification.
*/
int size();
/**
* Returns {@code true} if this multimap contains no key-value pairs. Equivalent
* to {@code size() == 0}, but can in some cases be more efficient.
*/
boolean isEmpty();
/**
* Returns {@code true} if this multimap contains at least one key-value pair
* with the key {@code key}.
*/
boolean containsKey(@Nullable Object key);
/**
* Returns {@code true} if this multimap contains at least one key-value pair
* with the value {@code value}.
*/
boolean containsValue(@Nullable Object value);
/**
* Returns {@code true} if this multimap contains at least one key-value pair
* with the key {@code key} and the value {@code value}.
*/
boolean containsEntry(@Nullable Object key, @Nullable Object value);
// Modification Operations
/**
* Stores a key-value pair in this multimap.
*
* <p>
* Some multimap implementations allow duplicate key-value pairs, in which case
* {@code put} always adds a new key-value pair and increases the multimap size
* by 1. Other implementations prohibit duplicates, and storing a key-value pair
* that's already in the multimap has no effect.
*
* @return {@code true} if the method increased the size of the multimap, or
* {@code false} if the multimap already contained the key-value pair
* and doesn't allow duplicates
*/
boolean put(@Nullable K key, @Nullable V value);
/**
* Removes a single key-value pair with the key {@code key} and the value
* {@code value} from this multimap, if such exists. If multiple key-value pairs
* in the multimap fit this description, which one is removed is unspecified.
*
* @return {@code true} if the multimap changed
*/
boolean remove(@Nullable Object key, @Nullable Object value);
// Bulk Operations
/**
* Stores a key-value pair in this multimap for each of {@code values}, all
* using the same key, {@code key}. Equivalent to (but expected to be more
* efficient than):
*
* <pre>
* {@code
*
* for (V value : values) {
* put(key, value);
* }}
* </pre>
*
* <p>
* In particular, this is a no-op if {@code values} is empty.
*
* @return {@code true} if the multimap changed
*/
boolean putAll(@Nullable K key, Iterable<? extends V> values);
/**
* Stores all key-value pairs of {@code multimap} in this multimap, in the order
* returned by {@code multimap.entries()}.
*
* @return {@code true} if the multimap changed
*/
boolean putAll(Multimap<? extends K, ? extends V> multimap);
/**
* Stores a collection of values with the same key, replacing any existing
* values for that key.
*
* <p>
* If {@code values} is empty, this is equivalent to {@link #removeAll(Object)
* removeAll(key)}.
*
* @return the collection of replaced values, or an empty collection if no
* values were previously associated with the key. The collection
* <i>may</i> be modifiable, but updating it will have no effect on the
* multimap.
*/
Collection<V> replaceValues(@Nullable K key, Iterable<? extends V> values);
/**
* Removes all values associated with the key {@code key}.
*
* <p>
* Once this method returns, {@code key} will not be mapped to any values, so it
* will not appear in {@link #keySet()}, {@link #asMap()}, or any other views.
*
* @return the values that were removed (possibly empty). The returned
* collection <i>may</i> be modifiable, but updating it will have no
* effect on the multimap.
*/
Collection<V> removeAll(@Nullable Object key);
/**
* Removes all key-value pairs from the multimap, leaving it
* {@linkplain #isEmpty empty}.
*/
void clear();
// Views
/**
* Returns a view collection of the values associated with {@code key} in this
* multimap, if any. Note that when {@code containsKey(key)} is false, this
* returns an empty collection, not {@code null}.
*
* <p>
* Changes to the returned collection will update the underlying multimap, and
* vice versa.
*/
Collection<V> get(@Nullable K key);
/**
* Returns a view collection of all <i>distinct</i> keys contained in this
* multimap. Note that the key set contains a key if and only if this multimap
* maps that key to at least one value.
*
* <p>
* Changes to the returned set will update the underlying multimap, and vice
* versa. However, <i>adding</i> to the returned set is not possible.
*/
Set<K> keySet();
/**
* Returns a view collection containing the key from each key-value pair in this
* multimap, <i>without</i> collapsing duplicates. This collection has the same
* size as this multimap, and {@code keys().count(k) ==
* get(k).size()} for all {@code k}.
*
* <p>
* Changes to the returned multiset will update the underlying multimap, and
* vice versa. However, <i>adding</i> to the returned collection is not
* possible.
*/
Multiset<K> keys();
/**
* Returns a view collection containing the <i>value</i> from each key-value
* pair contained in this multimap, without collapsing duplicates (so {@code
* values().size() == size()}).
*
* <p>
* Changes to the returned collection will update the underlying multimap, and
* vice versa. However, <i>adding</i> to the returned collection is not
* possible.
*/
Collection<V> values();
/**
* Returns a view collection of all key-value pairs contained in this multimap,
* as {@link Map.Entry} instances.
*
* <p>
* Changes to the returned collection or the entries it contains will update the
* underlying multimap, and vice versa. However, <i>adding</i> to the returned
* collection is not possible.
*/
Collection<Map.Entry<K, V>> entries();
/**
* Returns a view of this multimap as a {@code Map} from each distinct key to
* the nonempty 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 multimap; otherwise it returns {@code
* null} as opposed to an empty collection.
*
* <p>
* Changes to the returned map or the collections that serve as its values will
* update the underlying multimap, and vice versa. The map does not support
* {@code put} or {@code putAll}, nor do its entries support
* {@link Map.Entry#setValue setValue}.
*/
Map<K, Collection<V>> asMap();
// Comparison and hashing
/**
* Compares the specified object with this multimap for equality. Two multimaps
* are equal when their map views, as returned by {@link #asMap}, are also
* equal.
*
* <p>
* In general, two multimaps with identical key-value mappings may or may not be
* equal, depending on the implementation. For example, two {@link SetMultimap}
* instances with the same key-value mappings are equal, but equality of two
* {@link ListMultimap} instances depends on the ordering of the values for each
* key.
*
* <p>
* A non-empty {@link SetMultimap} cannot be equal to a non-empty
* {@link ListMultimap}, since their {@link #asMap} views contain unequal
* collections as values. However, any two empty multimaps are equal, because
* they both have empty {@link #asMap} views.
*/
@Override
boolean equals(@Nullable Object obj);
/**
* Returns the hash code for this multimap.
*
* <p>
* The hash code of a multimap is defined as the hash code of the map view, as
* returned by {@link Multimap#asMap}.
*/
@Override
int hashCode();
}