EaglerForge/sources/main/java/com/google/common/collect/Multimaps.java

/*
 * 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 static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.CollectPreconditions.checkNonnegative;
import static com.google.common.collect.CollectPreconditions.checkRemove;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.SortedSet;

import javax.annotation.Nullable;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Function;
import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import com.google.common.base.Supplier;
import com.google.common.collect.Maps.EntryTransformer;

/**
 * Provides static methods acting on or generating a {@code Multimap}.
 *
 * <p>
 * See the Guava User Guide article on <a href=
 * "http://code.google.com/p/guava-libraries/wiki/CollectionUtilitiesExplained#Multimaps">
 * {@code Multimaps}</a>.
 *
 * @author Jared Levy
 * @author Robert Konigsberg
 * @author Mike Bostock
 * @author Louis Wasserman
 * @since 2.0 (imported from Google Collections Library)
 */
@GwtCompatible(emulated = true)
public final class Multimaps {
	private Multimaps() {
	}

	/**
	 * Creates a new {@code Multimap} backed by {@code map}, whose internal value
	 * collections are generated by {@code factory}.
	 *
	 * <b>Warning: do not use</b> this method when the collections returned by
	 * {@code factory} implement either {@link List} or {@code Set}! Use the more
	 * specific method {@link #newListMultimap}, {@link #newSetMultimap} or
	 * {@link #newSortedSetMultimap} instead, to avoid very surprising behavior from
	 * {@link Multimap#equals}.
	 *
	 * <p>
	 * The {@code factory}-generated and {@code map} classes determine the multimap
	 * iteration order. They also specify the behavior of the {@code equals},
	 * {@code hashCode}, and {@code toString} methods for the multimap and its
	 * returned views. However, the multimap's {@code get} method returns instances
	 * of a different class than {@code factory.get()} does.
	 *
	 * <p>
	 * The multimap is serializable if {@code map}, {@code factory}, the collections
	 * generated by {@code factory}, and the multimap contents are all serializable.
	 *
	 * <p>
	 * The multimap is not threadsafe when any concurrent operations update the
	 * multimap, even if {@code map} and the instances generated by {@code factory}
	 * are. Concurrent read operations will work correctly. To allow concurrent
	 * update operations, wrap the multimap with a call to
	 * {@link #synchronizedMultimap}.
	 *
	 * <p>
	 * Call this method only when the simpler methods
	 * {@link ArrayListMultimap#create()}, {@link HashMultimap#create()},
	 * {@link LinkedHashMultimap#create()}, {@link LinkedListMultimap#create()},
	 * {@link TreeMultimap#create()}, and
	 * {@link TreeMultimap#create(Comparator, Comparator)} won't suffice.
	 *
	 * <p>
	 * Note: the multimap assumes complete ownership over of {@code map} and the
	 * collections returned by {@code factory}. Those objects should not be manually
	 * updated and they should not use soft, weak, or phantom references.
	 *
	 * @param map     place to store the mapping from each key to its corresponding
	 *                values
	 * @param factory supplier of new, empty collections that will each hold all
	 *                values for a given key
	 * @throws IllegalArgumentException if {@code map} is not empty
	 */
	public static <K, V> Multimap<K, V> newMultimap(Map<K, Collection<V>> map,
			final Supplier<? extends Collection<V>> factory) {
		return new CustomMultimap<K, V>(map, factory);
	}

	private static class CustomMultimap<K, V> extends AbstractMapBasedMultimap<K, V> {
		transient Supplier<? extends Collection<V>> factory;

		CustomMultimap(Map<K, Collection<V>> map, Supplier<? extends Collection<V>> factory) {
			super(map);
			this.factory = checkNotNull(factory);
		}

		@Override
		protected Collection<V> createCollection() {
			return factory.get();
		}

		// can't use Serialization writeMultimap and populateMultimap methods since
		// there's no way to generate the empty backing map.

		/** @serialData the factory and the backing map */
		@GwtIncompatible("java.io.ObjectOutputStream")
		private void writeObject(ObjectOutputStream stream) throws IOException {
			stream.defaultWriteObject();
			stream.writeObject(factory);
			stream.writeObject(backingMap());
		}

		@GwtIncompatible("java.io.ObjectInputStream")
		@SuppressWarnings("unchecked") // reading data stored by writeObject
		private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
			stream.defaultReadObject();
			factory = (Supplier<? extends Collection<V>>) stream.readObject();
			Map<K, Collection<V>> map = (Map<K, Collection<V>>) stream.readObject();
			setMap(map);
		}

		@GwtIncompatible("java serialization not supported")
		private static final long serialVersionUID = 0;
	}

	/**
	 * Creates a new {@code ListMultimap} that uses the provided map and factory. It
	 * can generate a multimap based on arbitrary {@link Map} and {@link List}
	 * classes.
	 *
	 * <p>
	 * The {@code factory}-generated and {@code map} classes determine the multimap
	 * iteration order. They also specify the behavior of the {@code equals},
	 * {@code hashCode}, and {@code toString} methods for the multimap and its
	 * returned views. The multimap's {@code get}, {@code
	 * removeAll}, and {@code replaceValues} methods return {@code RandomAccess}
	 * lists if the factory does. However, the multimap's {@code get} method returns
	 * instances of a different class than does {@code factory.get()}.
	 *
	 * <p>
	 * The multimap is serializable if {@code map}, {@code factory}, the lists
	 * generated by {@code factory}, and the multimap contents are all serializable.
	 *
	 * <p>
	 * The multimap is not threadsafe when any concurrent operations update the
	 * multimap, even if {@code map} and the instances generated by {@code factory}
	 * are. Concurrent read operations will work correctly. To allow concurrent
	 * update operations, wrap the multimap with a call to
	 * {@link #synchronizedListMultimap}.
	 *
	 * <p>
	 * Call this method only when the simpler methods
	 * {@link ArrayListMultimap#create()} and {@link LinkedListMultimap#create()}
	 * won't suffice.
	 *
	 * <p>
	 * Note: the multimap assumes complete ownership over of {@code map} and the
	 * lists returned by {@code factory}. Those objects should not be manually
	 * updated, they should be empty when provided, and they should not use soft,
	 * weak, or phantom references.
	 *
	 * @param map     place to store the mapping from each key to its corresponding
	 *                values
	 * @param factory supplier of new, empty lists that will each hold all values
	 *                for a given key
	 * @throws IllegalArgumentException if {@code map} is not empty
	 */
	public static <K, V> ListMultimap<K, V> newListMultimap(Map<K, Collection<V>> map,
			final Supplier<? extends List<V>> factory) {
		return new CustomListMultimap<K, V>(map, factory);
	}

	private static class CustomListMultimap<K, V> extends AbstractListMultimap<K, V> {
		transient Supplier<? extends List<V>> factory;

		CustomListMultimap(Map<K, Collection<V>> map, Supplier<? extends List<V>> factory) {
			super(map);
			this.factory = checkNotNull(factory);
		}

		@Override
		protected List<V> createCollection() {
			return factory.get();
		}

		/** @serialData the factory and the backing map */
		@GwtIncompatible("java.io.ObjectOutputStream")
		private void writeObject(ObjectOutputStream stream) throws IOException {
			stream.defaultWriteObject();
			stream.writeObject(factory);
			stream.writeObject(backingMap());
		}

		@GwtIncompatible("java.io.ObjectInputStream")
		@SuppressWarnings("unchecked") // reading data stored by writeObject
		private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
			stream.defaultReadObject();
			factory = (Supplier<? extends List<V>>) stream.readObject();
			Map<K, Collection<V>> map = (Map<K, Collection<V>>) stream.readObject();
			setMap(map);
		}

		@GwtIncompatible("java serialization not supported")
		private static final long serialVersionUID = 0;
	}

	/**
	 * Creates a new {@code SetMultimap} that uses the provided map and factory. It
	 * can generate a multimap based on arbitrary {@link Map} and {@link Set}
	 * classes.
	 *
	 * <p>
	 * The {@code factory}-generated and {@code map} classes determine the multimap
	 * iteration order. They also specify the behavior of the {@code equals},
	 * {@code hashCode}, and {@code toString} methods for the multimap and its
	 * returned views. However, the multimap's {@code get} method returns instances
	 * of a different class than {@code factory.get()} does.
	 *
	 * <p>
	 * The multimap is serializable if {@code map}, {@code factory}, the sets
	 * generated by {@code factory}, and the multimap contents are all serializable.
	 *
	 * <p>
	 * The multimap is not threadsafe when any concurrent operations update the
	 * multimap, even if {@code map} and the instances generated by {@code factory}
	 * are. Concurrent read operations will work correctly. To allow concurrent
	 * update operations, wrap the multimap with a call to
	 * {@link #synchronizedSetMultimap}.
	 *
	 * <p>
	 * Call this method only when the simpler methods {@link HashMultimap#create()},
	 * {@link LinkedHashMultimap#create()}, {@link TreeMultimap#create()}, and
	 * {@link TreeMultimap#create(Comparator, Comparator)} won't suffice.
	 *
	 * <p>
	 * Note: the multimap assumes complete ownership over of {@code map} and the
	 * sets returned by {@code factory}. Those objects should not be manually
	 * updated and they should not use soft, weak, or phantom references.
	 *
	 * @param map     place to store the mapping from each key to its corresponding
	 *                values
	 * @param factory supplier of new, empty sets that will each hold all values for
	 *                a given key
	 * @throws IllegalArgumentException if {@code map} is not empty
	 */
	public static <K, V> SetMultimap<K, V> newSetMultimap(Map<K, Collection<V>> map,
			final Supplier<? extends Set<V>> factory) {
		return new CustomSetMultimap<K, V>(map, factory);
	}

	private static class CustomSetMultimap<K, V> extends AbstractSetMultimap<K, V> {
		transient Supplier<? extends Set<V>> factory;

		CustomSetMultimap(Map<K, Collection<V>> map, Supplier<? extends Set<V>> factory) {
			super(map);
			this.factory = checkNotNull(factory);
		}

		@Override
		protected Set<V> createCollection() {
			return factory.get();
		}

		/** @serialData the factory and the backing map */
		@GwtIncompatible("java.io.ObjectOutputStream")
		private void writeObject(ObjectOutputStream stream) throws IOException {
			stream.defaultWriteObject();
			stream.writeObject(factory);
			stream.writeObject(backingMap());
		}

		@GwtIncompatible("java.io.ObjectInputStream")
		@SuppressWarnings("unchecked") // reading data stored by writeObject
		private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
			stream.defaultReadObject();
			factory = (Supplier<? extends Set<V>>) stream.readObject();
			Map<K, Collection<V>> map = (Map<K, Collection<V>>) stream.readObject();
			setMap(map);
		}

		@GwtIncompatible("not needed in emulated source")
		private static final long serialVersionUID = 0;
	}

	/**
	 * Creates a new {@code SortedSetMultimap} that uses the provided map and
	 * factory. It can generate a multimap based on arbitrary {@link Map} and
	 * {@link SortedSet} classes.
	 *
	 * <p>
	 * The {@code factory}-generated and {@code map} classes determine the multimap
	 * iteration order. They also specify the behavior of the {@code equals},
	 * {@code hashCode}, and {@code toString} methods for the multimap and its
	 * returned views. However, the multimap's {@code get} method returns instances
	 * of a different class than {@code factory.get()} does.
	 *
	 * <p>
	 * The multimap is serializable if {@code map}, {@code factory}, the sets
	 * generated by {@code factory}, and the multimap contents are all serializable.
	 *
	 * <p>
	 * The multimap is not threadsafe when any concurrent operations update the
	 * multimap, even if {@code map} and the instances generated by {@code factory}
	 * are. Concurrent read operations will work correctly. To allow concurrent
	 * update operations, wrap the multimap with a call to
	 * {@link #synchronizedSortedSetMultimap}.
	 *
	 * <p>
	 * Call this method only when the simpler methods {@link TreeMultimap#create()}
	 * and {@link TreeMultimap#create(Comparator, Comparator)} won't suffice.
	 *
	 * <p>
	 * Note: the multimap assumes complete ownership over of {@code map} and the
	 * sets returned by {@code factory}. Those objects should not be manually
	 * updated and they should not use soft, weak, or phantom references.
	 *
	 * @param map     place to store the mapping from each key to its corresponding
	 *                values
	 * @param factory supplier of new, empty sorted sets that will each hold all
	 *                values for a given key
	 * @throws IllegalArgumentException if {@code map} is not empty
	 */
	public static <K, V> SortedSetMultimap<K, V> newSortedSetMultimap(Map<K, Collection<V>> map,
			final Supplier<? extends SortedSet<V>> factory) {
		return new CustomSortedSetMultimap<K, V>(map, factory);
	}

	private static class CustomSortedSetMultimap<K, V> extends AbstractSortedSetMultimap<K, V> {
		transient Supplier<? extends SortedSet<V>> factory;
		transient Comparator<? super V> valueComparator;

		CustomSortedSetMultimap(Map<K, Collection<V>> map, Supplier<? extends SortedSet<V>> factory) {
			super(map);
			this.factory = checkNotNull(factory);
			valueComparator = factory.get().comparator();
		}

		@Override
		protected SortedSet<V> createCollection() {
			return factory.get();
		}

		@Override
		public Comparator<? super V> valueComparator() {
			return valueComparator;
		}

		/** @serialData the factory and the backing map */
		@GwtIncompatible("java.io.ObjectOutputStream")
		private void writeObject(ObjectOutputStream stream) throws IOException {
			stream.defaultWriteObject();
			stream.writeObject(factory);
			stream.writeObject(backingMap());
		}

		@GwtIncompatible("java.io.ObjectInputStream")
		@SuppressWarnings("unchecked") // reading data stored by writeObject
		private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
			stream.defaultReadObject();
			factory = (Supplier<? extends SortedSet<V>>) stream.readObject();
			valueComparator = factory.get().comparator();
			Map<K, Collection<V>> map = (Map<K, Collection<V>>) stream.readObject();
			setMap(map);
		}

		@GwtIncompatible("not needed in emulated source")
		private static final long serialVersionUID = 0;
	}

	/**
	 * Copies each key-value mapping in {@code source} into {@code dest}, with its
	 * key and value reversed.
	 *
	 * <p>
	 * If {@code source} is an {@link ImmutableMultimap}, consider using
	 * {@link ImmutableMultimap#inverse} instead.
	 *
	 * @param source any multimap
	 * @param dest   the multimap to copy into; usually empty
	 * @return {@code dest}
	 */
	public static <K, V, M extends Multimap<K, V>> M invertFrom(Multimap<? extends V, ? extends K> source, M dest) {
		checkNotNull(dest);
		for (Map.Entry<? extends V, ? extends K> entry : source.entries()) {
			dest.put(entry.getValue(), entry.getKey());
		}
		return dest;
	}

	/**
	 * Returns a synchronized (thread-safe) multimap backed by the specified
	 * multimap. In order to guarantee serial access, it is critical that <b>all</b>
	 * access to the backing multimap is accomplished through the returned multimap.
	 *
	 * <p>
	 * It is imperative that the user manually synchronize on the returned multimap
	 * when accessing any of its collection views:
	 * 
	 * <pre>
	 *    {@code
	 *
	 *   Multimap<K, V> multimap = Multimaps.synchronizedMultimap(
	 *       HashMultimap.<K, V>create());
	 *   ...
	 *   Collection<V> values = multimap.get(key);  // Needn't be in synchronized block
	 *   ...
	 *   synchronized (multimap) {  // Synchronizing on multimap, not values!
	 *     Iterator<V> i = values.iterator(); // Must be in synchronized block
	 *     while (i.hasNext()) {
	 *       foo(i.next());
	 *     }
	 *   }}
	 * </pre>
	 *
	 * <p>
	 * Failure to follow this advice may result in non-deterministic behavior.
	 *
	 * <p>
	 * Note that the generated multimap's {@link Multimap#removeAll} and
	 * {@link Multimap#replaceValues} methods return collections that aren't
	 * synchronized.
	 *
	 * <p>
	 * The returned multimap will be serializable if the specified multimap is
	 * serializable.
	 *
	 * @param multimap the multimap to be wrapped in a synchronized view
	 * @return a synchronized view of the specified multimap
	 */
	public static <K, V> Multimap<K, V> synchronizedMultimap(Multimap<K, V> multimap) {
		return Synchronized.multimap(multimap, null);
	}

	/**
	 * Returns an unmodifiable view of the specified multimap. Query operations on
	 * the returned multimap "read through" to the specified multimap, and attempts
	 * to modify the returned multimap, either directly or through the multimap's
	 * views, result in an {@code UnsupportedOperationException}.
	 *
	 * <p>
	 * Note that the generated multimap's {@link Multimap#removeAll} and
	 * {@link Multimap#replaceValues} methods return collections that are
	 * modifiable.
	 *
	 * <p>
	 * The returned multimap will be serializable if the specified multimap is
	 * serializable.
	 *
	 * @param delegate the multimap for which an unmodifiable view is to be returned
	 * @return an unmodifiable view of the specified multimap
	 */
	public static <K, V> Multimap<K, V> unmodifiableMultimap(Multimap<K, V> delegate) {
		if (delegate instanceof UnmodifiableMultimap || delegate instanceof ImmutableMultimap) {
			return delegate;
		}
		return new UnmodifiableMultimap<K, V>(delegate);
	}

	/**
	 * Simply returns its argument.
	 *
	 * @deprecated no need to use this
	 * @since 10.0
	 */
	@Deprecated
	public static <K, V> Multimap<K, V> unmodifiableMultimap(ImmutableMultimap<K, V> delegate) {
		return checkNotNull(delegate);
	}

	private static class UnmodifiableMultimap<K, V> extends ForwardingMultimap<K, V> implements Serializable {
		final Multimap<K, V> delegate;
		transient Collection<Entry<K, V>> entries;
		transient Multiset<K> keys;
		transient Set<K> keySet;
		transient Collection<V> values;
		transient Map<K, Collection<V>> map;

		UnmodifiableMultimap(final Multimap<K, V> delegate) {
			this.delegate = checkNotNull(delegate);
		}

		@Override
		protected Multimap<K, V> delegate() {
			return delegate;
		}

		@Override
		public void clear() {
			throw new UnsupportedOperationException();
		}

		@Override
		public Map<K, Collection<V>> asMap() {
			Map<K, Collection<V>> result = map;
			if (result == null) {
				result = map = Collections.unmodifiableMap(
						Maps.transformValues(delegate.asMap(), new Function<Collection<V>, Collection<V>>() {
							@Override
							public Collection<V> apply(Collection<V> collection) {
								return unmodifiableValueCollection(collection);
							}
						}));
			}
			return result;
		}

		@Override
		public Collection<Entry<K, V>> entries() {
			Collection<Entry<K, V>> result = entries;
			if (result == null) {
				entries = result = unmodifiableEntries(delegate.entries());
			}
			return result;
		}

		@Override
		public Collection<V> get(K key) {
			return unmodifiableValueCollection(delegate.get(key));
		}

		@Override
		public Multiset<K> keys() {
			Multiset<K> result = keys;
			if (result == null) {
				keys = result = Multisets.unmodifiableMultiset(delegate.keys());
			}
			return result;
		}

		@Override
		public Set<K> keySet() {
			Set<K> result = keySet;
			if (result == null) {
				keySet = result = Collections.unmodifiableSet(delegate.keySet());
			}
			return result;
		}

		@Override
		public boolean put(K key, V value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean putAll(K key, Iterable<? extends V> values) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean putAll(Multimap<? extends K, ? extends V> multimap) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean remove(Object key, Object value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public Collection<V> removeAll(Object key) {
			throw new UnsupportedOperationException();
		}

		@Override
		public Collection<V> replaceValues(K key, Iterable<? extends V> values) {
			throw new UnsupportedOperationException();
		}

		@Override
		public Collection<V> values() {
			Collection<V> result = values;
			if (result == null) {
				values = result = Collections.unmodifiableCollection(delegate.values());
			}
			return result;
		}

		private static final long serialVersionUID = 0;
	}

	private static class UnmodifiableListMultimap<K, V> extends UnmodifiableMultimap<K, V>
			implements ListMultimap<K, V> {
		UnmodifiableListMultimap(ListMultimap<K, V> delegate) {
			super(delegate);
		}

		@Override
		public ListMultimap<K, V> delegate() {
			return (ListMultimap<K, V>) super.delegate();
		}

		@Override
		public List<V> get(K key) {
			return Collections.unmodifiableList(delegate().get(key));
		}

		@Override
		public List<V> removeAll(Object key) {
			throw new UnsupportedOperationException();
		}

		@Override
		public List<V> replaceValues(K key, Iterable<? extends V> values) {
			throw new UnsupportedOperationException();
		}

		private static final long serialVersionUID = 0;
	}

	private static class UnmodifiableSetMultimap<K, V> extends UnmodifiableMultimap<K, V> implements SetMultimap<K, V> {
		UnmodifiableSetMultimap(SetMultimap<K, V> delegate) {
			super(delegate);
		}

		@Override
		public SetMultimap<K, V> delegate() {
			return (SetMultimap<K, V>) super.delegate();
		}

		@Override
		public Set<V> get(K key) {
			/*
			 * Note that this doesn't return a SortedSet when delegate is a
			 * SortedSetMultiset, unlike (SortedSet<V>) super.get().
			 */
			return Collections.unmodifiableSet(delegate().get(key));
		}

		@Override
		public Set<Map.Entry<K, V>> entries() {
			return Maps.unmodifiableEntrySet(delegate().entries());
		}

		@Override
		public Set<V> removeAll(Object key) {
			throw new UnsupportedOperationException();
		}

		@Override
		public Set<V> replaceValues(K key, Iterable<? extends V> values) {
			throw new UnsupportedOperationException();
		}

		private static final long serialVersionUID = 0;
	}

	private static class UnmodifiableSortedSetMultimap<K, V> extends UnmodifiableSetMultimap<K, V>
			implements SortedSetMultimap<K, V> {
		UnmodifiableSortedSetMultimap(SortedSetMultimap<K, V> delegate) {
			super(delegate);
		}

		@Override
		public SortedSetMultimap<K, V> delegate() {
			return (SortedSetMultimap<K, V>) super.delegate();
		}

		@Override
		public SortedSet<V> get(K key) {
			return Collections.unmodifiableSortedSet(delegate().get(key));
		}

		@Override
		public SortedSet<V> removeAll(Object key) {
			throw new UnsupportedOperationException();
		}

		@Override
		public SortedSet<V> replaceValues(K key, Iterable<? extends V> values) {
			throw new UnsupportedOperationException();
		}

		@Override
		public Comparator<? super V> valueComparator() {
			return delegate().valueComparator();
		}

		private static final long serialVersionUID = 0;
	}

	/**
	 * Returns a synchronized (thread-safe) {@code SetMultimap} backed by the
	 * specified multimap.
	 *
	 * <p>
	 * You must follow the warnings described in {@link #synchronizedMultimap}.
	 *
	 * <p>
	 * The returned multimap will be serializable if the specified multimap is
	 * serializable.
	 *
	 * @param multimap the multimap to be wrapped
	 * @return a synchronized view of the specified multimap
	 */
	public static <K, V> SetMultimap<K, V> synchronizedSetMultimap(SetMultimap<K, V> multimap) {
		return Synchronized.setMultimap(multimap, null);
	}

	/**
	 * Returns an unmodifiable view of the specified {@code SetMultimap}. Query
	 * operations on the returned multimap "read through" to the specified multimap,
	 * and attempts to modify the returned multimap, either directly or through the
	 * multimap's views, result in an {@code UnsupportedOperationException}.
	 *
	 * <p>
	 * Note that the generated multimap's {@link Multimap#removeAll} and
	 * {@link Multimap#replaceValues} methods return collections that are
	 * modifiable.
	 *
	 * <p>
	 * The returned multimap will be serializable if the specified multimap is
	 * serializable.
	 *
	 * @param delegate the multimap for which an unmodifiable view is to be returned
	 * @return an unmodifiable view of the specified multimap
	 */
	public static <K, V> SetMultimap<K, V> unmodifiableSetMultimap(SetMultimap<K, V> delegate) {
		if (delegate instanceof UnmodifiableSetMultimap || delegate instanceof ImmutableSetMultimap) {
			return delegate;
		}
		return new UnmodifiableSetMultimap<K, V>(delegate);
	}

	/**
	 * Simply returns its argument.
	 *
	 * @deprecated no need to use this
	 * @since 10.0
	 */
	@Deprecated
	public static <K, V> SetMultimap<K, V> unmodifiableSetMultimap(ImmutableSetMultimap<K, V> delegate) {
		return checkNotNull(delegate);
	}

	/**
	 * Returns a synchronized (thread-safe) {@code SortedSetMultimap} backed by the
	 * specified multimap.
	 *
	 * <p>
	 * You must follow the warnings described in {@link #synchronizedMultimap}.
	 *
	 * <p>
	 * The returned multimap will be serializable if the specified multimap is
	 * serializable.
	 *
	 * @param multimap the multimap to be wrapped
	 * @return a synchronized view of the specified multimap
	 */
	public static <K, V> SortedSetMultimap<K, V> synchronizedSortedSetMultimap(SortedSetMultimap<K, V> multimap) {
		return Synchronized.sortedSetMultimap(multimap, null);
	}

	/**
	 * Returns an unmodifiable view of the specified {@code SortedSetMultimap}.
	 * Query operations on the returned multimap "read through" to the specified
	 * multimap, and attempts to modify the returned multimap, either directly or
	 * through the multimap's views, result in an
	 * {@code UnsupportedOperationException}.
	 *
	 * <p>
	 * Note that the generated multimap's {@link Multimap#removeAll} and
	 * {@link Multimap#replaceValues} methods return collections that are
	 * modifiable.
	 *
	 * <p>
	 * The returned multimap will be serializable if the specified multimap is
	 * serializable.
	 *
	 * @param delegate the multimap for which an unmodifiable view is to be returned
	 * @return an unmodifiable view of the specified multimap
	 */
	public static <K, V> SortedSetMultimap<K, V> unmodifiableSortedSetMultimap(SortedSetMultimap<K, V> delegate) {
		if (delegate instanceof UnmodifiableSortedSetMultimap) {
			return delegate;
		}
		return new UnmodifiableSortedSetMultimap<K, V>(delegate);
	}

	/**
	 * Returns a synchronized (thread-safe) {@code ListMultimap} backed by the
	 * specified multimap.
	 *
	 * <p>
	 * You must follow the warnings described in {@link #synchronizedMultimap}.
	 *
	 * @param multimap the multimap to be wrapped
	 * @return a synchronized view of the specified multimap
	 */
	public static <K, V> ListMultimap<K, V> synchronizedListMultimap(ListMultimap<K, V> multimap) {
		return Synchronized.listMultimap(multimap, null);
	}

	/**
	 * Returns an unmodifiable view of the specified {@code ListMultimap}. Query
	 * operations on the returned multimap "read through" to the specified multimap,
	 * and attempts to modify the returned multimap, either directly or through the
	 * multimap's views, result in an {@code UnsupportedOperationException}.
	 *
	 * <p>
	 * Note that the generated multimap's {@link Multimap#removeAll} and
	 * {@link Multimap#replaceValues} methods return collections that are
	 * modifiable.
	 *
	 * <p>
	 * The returned multimap will be serializable if the specified multimap is
	 * serializable.
	 *
	 * @param delegate the multimap for which an unmodifiable view is to be returned
	 * @return an unmodifiable view of the specified multimap
	 */
	public static <K, V> ListMultimap<K, V> unmodifiableListMultimap(ListMultimap<K, V> delegate) {
		if (delegate instanceof UnmodifiableListMultimap || delegate instanceof ImmutableListMultimap) {
			return delegate;
		}
		return new UnmodifiableListMultimap<K, V>(delegate);
	}

	/**
	 * Simply returns its argument.
	 *
	 * @deprecated no need to use this
	 * @since 10.0
	 */
	@Deprecated
	public static <K, V> ListMultimap<K, V> unmodifiableListMultimap(ImmutableListMultimap<K, V> delegate) {
		return checkNotNull(delegate);
	}

	/**
	 * Returns an unmodifiable view of the specified collection, preserving the
	 * interface for instances of {@code SortedSet}, {@code Set}, {@code List} and
	 * {@code Collection}, in that order of preference.
	 *
	 * @param collection the collection for which to return an unmodifiable view
	 * @return an unmodifiable view of the collection
	 */
	private static <V> Collection<V> unmodifiableValueCollection(Collection<V> collection) {
		if (collection instanceof SortedSet) {
			return Collections.unmodifiableSortedSet((SortedSet<V>) collection);
		} else if (collection instanceof Set) {
			return Collections.unmodifiableSet((Set<V>) collection);
		} else if (collection instanceof List) {
			return Collections.unmodifiableList((List<V>) collection);
		}
		return Collections.unmodifiableCollection(collection);
	}

	/**
	 * Returns an unmodifiable view of the specified collection of entries. The
	 * {@link Entry#setValue} operation throws an
	 * {@link UnsupportedOperationException}. If the specified collection is a
	 * {@code
	 * Set}, the returned collection is also a {@code Set}.
	 *
	 * @param entries the entries for which to return an unmodifiable view
	 * @return an unmodifiable view of the entries
	 */
	private static <K, V> Collection<Entry<K, V>> unmodifiableEntries(Collection<Entry<K, V>> entries) {
		if (entries instanceof Set) {
			return Maps.unmodifiableEntrySet((Set<Entry<K, V>>) entries);
		}
		return new Maps.UnmodifiableEntries<K, V>(Collections.unmodifiableCollection(entries));
	}

	/**
	 * Returns {@link ListMultimap#asMap multimap.asMap()}, with its type corrected
	 * from {@code Map<K, Collection<V>>} to {@code Map<K, List<V>>}.
	 *
	 * @since 15.0
	 */
	@Beta
	@SuppressWarnings("unchecked")
	// safe by specification of ListMultimap.asMap()
	public static <K, V> Map<K, List<V>> asMap(ListMultimap<K, V> multimap) {
		return (Map<K, List<V>>) (Map<K, ?>) multimap.asMap();
	}

	/**
	 * Returns {@link SetMultimap#asMap multimap.asMap()}, with its type corrected
	 * from {@code Map<K, Collection<V>>} to {@code Map<K, Set<V>>}.
	 *
	 * @since 15.0
	 */
	@Beta
	@SuppressWarnings("unchecked")
	// safe by specification of SetMultimap.asMap()
	public static <K, V> Map<K, Set<V>> asMap(SetMultimap<K, V> multimap) {
		return (Map<K, Set<V>>) (Map<K, ?>) multimap.asMap();
	}

	/**
	 * Returns {@link SortedSetMultimap#asMap multimap.asMap()}, with its type
	 * corrected from {@code Map<K, Collection<V>>} to {@code Map<K, SortedSet<V>>}.
	 *
	 * @since 15.0
	 */
	@Beta
	@SuppressWarnings("unchecked")
	// safe by specification of SortedSetMultimap.asMap()
	public static <K, V> Map<K, SortedSet<V>> asMap(SortedSetMultimap<K, V> multimap) {
		return (Map<K, SortedSet<V>>) (Map<K, ?>) multimap.asMap();
	}

	/**
	 * Returns {@link Multimap#asMap multimap.asMap()}. This is provided for parity
	 * with the other more strongly-typed {@code asMap()} implementations.
	 *
	 * @since 15.0
	 */
	@Beta
	public static <K, V> Map<K, Collection<V>> asMap(Multimap<K, V> multimap) {
		return multimap.asMap();
	}

	/**
	 * Returns a multimap view of the specified map. The multimap is backed by the
	 * map, so changes to the map are reflected in the multimap, and vice versa. If
	 * the map is modified while an iteration over one of the multimap's collection
	 * views is in progress (except through the iterator's own {@code
	 * remove} operation, or through the {@code setValue} operation on a map entry
	 * returned by the iterator), the results of the iteration are undefined.
	 *
	 * <p>
	 * The multimap supports mapping removal, which removes the corresponding
	 * mapping from the map. It does not support any operations which might add
	 * mappings, such as {@code put}, {@code putAll} or {@code replaceValues}.
	 *
	 * <p>
	 * The returned multimap will be serializable if the specified map is
	 * serializable.
	 *
	 * @param map the backing map for the returned multimap view
	 */
	public static <K, V> SetMultimap<K, V> forMap(Map<K, V> map) {
		return new MapMultimap<K, V>(map);
	}

	/** @see Multimaps#forMap */
	private static class MapMultimap<K, V> extends AbstractMultimap<K, V> implements SetMultimap<K, V>, Serializable {
		final Map<K, V> map;

		MapMultimap(Map<K, V> map) {
			this.map = checkNotNull(map);
		}

		@Override
		public int size() {
			return map.size();
		}

		@Override
		public boolean containsKey(Object key) {
			return map.containsKey(key);
		}

		@Override
		public boolean containsValue(Object value) {
			return map.containsValue(value);
		}

		@Override
		public boolean containsEntry(Object key, Object value) {
			return map.entrySet().contains(Maps.immutableEntry(key, value));
		}

		@Override
		public Set<V> get(final K key) {
			return new Sets.ImprovedAbstractSet<V>() {
				@Override
				public Iterator<V> iterator() {
					return new Iterator<V>() {
						int i;

						@Override
						public boolean hasNext() {
							return (i == 0) && map.containsKey(key);
						}

						@Override
						public V next() {
							if (!hasNext()) {
								throw new NoSuchElementException();
							}
							i++;
							return map.get(key);
						}

						@Override
						public void remove() {
							checkRemove(i == 1);
							i = -1;
							map.remove(key);
						}
					};
				}

				@Override
				public int size() {
					return map.containsKey(key) ? 1 : 0;
				}
			};
		}

		@Override
		public boolean put(K key, V value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean putAll(K key, Iterable<? extends V> values) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean putAll(Multimap<? extends K, ? extends V> multimap) {
			throw new UnsupportedOperationException();
		}

		@Override
		public Set<V> replaceValues(K key, Iterable<? extends V> values) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean remove(Object key, Object value) {
			return map.entrySet().remove(Maps.immutableEntry(key, value));
		}

		@Override
		public Set<V> removeAll(Object key) {
			Set<V> values = new HashSet<V>(2);
			if (!map.containsKey(key)) {
				return values;
			}
			values.add(map.remove(key));
			return values;
		}

		@Override
		public void clear() {
			map.clear();
		}

		@Override
		public Set<K> keySet() {
			return map.keySet();
		}

		@Override
		public Collection<V> values() {
			return map.values();
		}

		@Override
		public Set<Entry<K, V>> entries() {
			return map.entrySet();
		}

		@Override
		Iterator<Entry<K, V>> entryIterator() {
			return map.entrySet().iterator();
		}

		@Override
		Map<K, Collection<V>> createAsMap() {
			return new AsMap<K, V>(this);
		}

		@Override
		public int hashCode() {
			return map.hashCode();
		}

		private static final long serialVersionUID = 7845222491160860175L;
	}

	/**
	 * Returns a view of a multimap where each value is transformed by a function.
	 * All other properties of the multimap, such as iteration order, are left
	 * intact. For example, the code:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	Multimap<String, Integer> multimap = ImmutableSetMultimap.of("a", 2, "b", -3, "b", -3, "a", 4, "c", 6);
	 * 	Function<Integer, String> square = new Function<Integer, String>() {
	 * 		public String apply(Integer in) {
	 * 			return Integer.toString(in * in);
	 * 		}
	 * 	};
	 * 	Multimap<String, String> transformed = Multimaps.transformValues(multimap, square);
	 * 	System.out.println(transformed);
	 * }
	 * </pre>
	 *
	 * ... prints {@code {a=[4, 16], b=[9, 9], c=[36]}}.
	 *
	 * <p>
	 * Changes in the underlying multimap are reflected in this view. Conversely,
	 * this view supports removal operations, and these are reflected in the
	 * underlying multimap.
	 *
	 * <p>
	 * It's acceptable for the underlying multimap to contain null keys, and even
	 * null values provided that the function is capable of accepting null input.
	 * The transformed multimap might contain null values, if the function sometimes
	 * gives a null result.
	 *
	 * <p>
	 * The returned multimap is not thread-safe or serializable, even if the
	 * underlying multimap is. The {@code equals} and {@code hashCode} methods of
	 * the returned multimap are meaningless, since there is not a definition of
	 * {@code equals} or {@code hashCode} for general collections, and {@code get()}
	 * will return a general {@code Collection} as opposed to a {@code List} or a
	 * {@code Set}.
	 *
	 * <p>
	 * The function is applied lazily, invoked when needed. This is necessary for
	 * the returned multimap to be a view, but it means that the function will be
	 * applied many times for bulk operations like {@link Multimap#containsValue}
	 * and {@code Multimap.toString()}. For this to perform well, {@code function}
	 * should be fast. To avoid lazy evaluation when the returned multimap doesn't
	 * need to be a view, copy the returned multimap into a new multimap of your
	 * choosing.
	 *
	 * @since 7.0
	 */
	public static <K, V1, V2> Multimap<K, V2> transformValues(Multimap<K, V1> fromMultimap,
			final Function<? super V1, V2> function) {
		checkNotNull(function);
		EntryTransformer<K, V1, V2> transformer = Maps.asEntryTransformer(function);
		return transformEntries(fromMultimap, transformer);
	}

	/**
	 * Returns a view of a multimap whose values are derived from the original
	 * multimap's entries. In contrast to {@link #transformValues}, this method's
	 * entry-transformation logic may depend on the key as well as the value.
	 *
	 * <p>
	 * All other properties of the transformed multimap, such as iteration order,
	 * are left intact. For example, the code:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	SetMultimap<String, Integer> multimap = ImmutableSetMultimap.of("a", 1, "a", 4, "b", -6);
	 * 	EntryTransformer<String, Integer, String> transformer = new EntryTransformer<String, Integer, String>() {
	 * 		public String transformEntry(String key, Integer value) {
	 * 			return (value >= 0) ? key : "no" + key;
	 * 		}
	 * 	};
	 * 	Multimap<String, String> transformed = Multimaps.transformEntries(multimap, transformer);
	 * 	System.out.println(transformed);
	 * }
	 * </pre>
	 *
	 * ... prints {@code {a=[a, a], b=[nob]}}.
	 *
	 * <p>
	 * Changes in the underlying multimap are reflected in this view. Conversely,
	 * this view supports removal operations, and these are reflected in the
	 * underlying multimap.
	 *
	 * <p>
	 * It's acceptable for the underlying multimap to contain null keys and null
	 * values provided that the transformer is capable of accepting null inputs. The
	 * transformed multimap might contain null values if the transformer sometimes
	 * gives a null result.
	 *
	 * <p>
	 * The returned multimap is not thread-safe or serializable, even if the
	 * underlying multimap is. The {@code equals} and {@code hashCode} methods of
	 * the returned multimap are meaningless, since there is not a definition of
	 * {@code equals} or {@code hashCode} for general collections, and {@code get()}
	 * will return a general {@code Collection} as opposed to a {@code List} or a
	 * {@code Set}.
	 *
	 * <p>
	 * The transformer is applied lazily, invoked when needed. This is necessary for
	 * the returned multimap to be a view, but it means that the transformer will be
	 * applied many times for bulk operations like {@link Multimap#containsValue}
	 * and {@link Object#toString}. For this to perform well, {@code transformer}
	 * should be fast. To avoid lazy evaluation when the returned multimap doesn't
	 * need to be a view, copy the returned multimap into a new multimap of your
	 * choosing.
	 *
	 * <p>
	 * <b>Warning:</b> This method assumes that for any instance {@code k} of
	 * {@code EntryTransformer} key type {@code K}, {@code k.equals(k2)} implies
	 * that {@code k2} is also of type {@code K}. Using an {@code
	 * EntryTransformer} key type for which this may not hold, such as {@code
	 * ArrayList}, may risk a {@code ClassCastException} when calling methods on the
	 * transformed multimap.
	 *
	 * @since 7.0
	 */
	public static <K, V1, V2> Multimap<K, V2> transformEntries(Multimap<K, V1> fromMap,
			EntryTransformer<? super K, ? super V1, V2> transformer) {
		return new TransformedEntriesMultimap<K, V1, V2>(fromMap, transformer);
	}

	private static class TransformedEntriesMultimap<K, V1, V2> extends AbstractMultimap<K, V2> {
		final Multimap<K, V1> fromMultimap;
		final EntryTransformer<? super K, ? super V1, V2> transformer;

		TransformedEntriesMultimap(Multimap<K, V1> fromMultimap,
				final EntryTransformer<? super K, ? super V1, V2> transformer) {
			this.fromMultimap = checkNotNull(fromMultimap);
			this.transformer = checkNotNull(transformer);
		}

		Collection<V2> transform(K key, Collection<V1> values) {
			Function<? super V1, V2> function = Maps.asValueToValueFunction(transformer, key);
			if (values instanceof List) {
				return Lists.transform((List<V1>) values, function);
			} else {
				return Collections2.transform(values, function);
			}
		}

		@Override
		Map<K, Collection<V2>> createAsMap() {
			return Maps.transformEntries(fromMultimap.asMap(),
					new EntryTransformer<K, Collection<V1>, Collection<V2>>() {
						@Override
						public Collection<V2> transformEntry(K key, Collection<V1> value) {
							return transform(key, value);
						}
					});
		}

		@Override
		public void clear() {
			fromMultimap.clear();
		}

		@Override
		public boolean containsKey(Object key) {
			return fromMultimap.containsKey(key);
		}

		@Override
		Iterator<Entry<K, V2>> entryIterator() {
			return Iterators.transform(fromMultimap.entries().iterator(),
					Maps.<K, V1, V2>asEntryToEntryFunction(transformer));
		}

		@Override
		public Collection<V2> get(final K key) {
			return transform(key, fromMultimap.get(key));
		}

		@Override
		public boolean isEmpty() {
			return fromMultimap.isEmpty();
		}

		@Override
		public Set<K> keySet() {
			return fromMultimap.keySet();
		}

		@Override
		public Multiset<K> keys() {
			return fromMultimap.keys();
		}

		@Override
		public boolean put(K key, V2 value) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean putAll(K key, Iterable<? extends V2> values) {
			throw new UnsupportedOperationException();
		}

		@Override
		public boolean putAll(Multimap<? extends K, ? extends V2> multimap) {
			throw new UnsupportedOperationException();
		}

		@SuppressWarnings("unchecked")
		@Override
		public boolean remove(Object key, Object value) {
			return get((K) key).remove(value);
		}

		@SuppressWarnings("unchecked")
		@Override
		public Collection<V2> removeAll(Object key) {
			return transform((K) key, fromMultimap.removeAll(key));
		}

		@Override
		public Collection<V2> replaceValues(K key, Iterable<? extends V2> values) {
			throw new UnsupportedOperationException();
		}

		@Override
		public int size() {
			return fromMultimap.size();
		}

		@Override
		Collection<V2> createValues() {
			return Collections2.transform(fromMultimap.entries(), Maps.<K, V1, V2>asEntryToValueFunction(transformer));
		}
	}

	/**
	 * Returns a view of a {@code ListMultimap} where each value is transformed by a
	 * function. All other properties of the multimap, such as iteration order, are
	 * left intact. For example, the code:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	ListMultimap<String, Integer> multimap = ImmutableListMultimap.of("a", 4, "a", 16, "b", 9);
	 * 	Function<Integer, Double> sqrt = new Function<Integer, Double>() {
	 * 		public Double apply(Integer in) {
	 * 			return Math.sqrt((int) in);
	 * 		}
	 * 	};
	 * 	ListMultimap<String, Double> transformed = Multimaps.transformValues(map, sqrt);
	 * 	System.out.println(transformed);
	 * }
	 * </pre>
	 *
	 * ... prints {@code {a=[2.0, 4.0], b=[3.0]}}.
	 *
	 * <p>
	 * Changes in the underlying multimap are reflected in this view. Conversely,
	 * this view supports removal operations, and these are reflected in the
	 * underlying multimap.
	 *
	 * <p>
	 * It's acceptable for the underlying multimap to contain null keys, and even
	 * null values provided that the function is capable of accepting null input.
	 * The transformed multimap might contain null values, if the function sometimes
	 * gives a null result.
	 *
	 * <p>
	 * The returned multimap is not thread-safe or serializable, even if the
	 * underlying multimap is.
	 *
	 * <p>
	 * The function is applied lazily, invoked when needed. This is necessary for
	 * the returned multimap to be a view, but it means that the function will be
	 * applied many times for bulk operations like {@link Multimap#containsValue}
	 * and {@code Multimap.toString()}. For this to perform well, {@code function}
	 * should be fast. To avoid lazy evaluation when the returned multimap doesn't
	 * need to be a view, copy the returned multimap into a new multimap of your
	 * choosing.
	 *
	 * @since 7.0
	 */
	public static <K, V1, V2> ListMultimap<K, V2> transformValues(ListMultimap<K, V1> fromMultimap,
			final Function<? super V1, V2> function) {
		checkNotNull(function);
		EntryTransformer<K, V1, V2> transformer = Maps.asEntryTransformer(function);
		return transformEntries(fromMultimap, transformer);
	}

	/**
	 * Returns a view of a {@code ListMultimap} whose values are derived from the
	 * original multimap's entries. In contrast to
	 * {@link #transformValues(ListMultimap, Function)}, this method's
	 * entry-transformation logic may depend on the key as well as the value.
	 *
	 * <p>
	 * All other properties of the transformed multimap, such as iteration order,
	 * are left intact. For example, the code:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	Multimap<String, Integer> multimap = ImmutableMultimap.of("a", 1, "a", 4, "b", 6);
	 * 	EntryTransformer<String, Integer, String> transformer = new EntryTransformer<String, Integer, String>() {
	 * 		public String transformEntry(String key, Integer value) {
	 * 			return key + value;
	 * 		}
	 * 	};
	 * 	Multimap<String, String> transformed = Multimaps.transformEntries(multimap, transformer);
	 * 	System.out.println(transformed);
	 * }
	 * </pre>
	 *
	 * ... prints {@code {"a"=["a1", "a4"], "b"=["b6"]}}.
	 *
	 * <p>
	 * Changes in the underlying multimap are reflected in this view. Conversely,
	 * this view supports removal operations, and these are reflected in the
	 * underlying multimap.
	 *
	 * <p>
	 * It's acceptable for the underlying multimap to contain null keys and null
	 * values provided that the transformer is capable of accepting null inputs. The
	 * transformed multimap might contain null values if the transformer sometimes
	 * gives a null result.
	 *
	 * <p>
	 * The returned multimap is not thread-safe or serializable, even if the
	 * underlying multimap is.
	 *
	 * <p>
	 * The transformer is applied lazily, invoked when needed. This is necessary for
	 * the returned multimap to be a view, but it means that the transformer will be
	 * applied many times for bulk operations like {@link Multimap#containsValue}
	 * and {@link Object#toString}. For this to perform well, {@code transformer}
	 * should be fast. To avoid lazy evaluation when the returned multimap doesn't
	 * need to be a view, copy the returned multimap into a new multimap of your
	 * choosing.
	 *
	 * <p>
	 * <b>Warning:</b> This method assumes that for any instance {@code k} of
	 * {@code EntryTransformer} key type {@code K}, {@code k.equals(k2)} implies
	 * that {@code k2} is also of type {@code K}. Using an {@code
	 * EntryTransformer} key type for which this may not hold, such as {@code
	 * ArrayList}, may risk a {@code ClassCastException} when calling methods on the
	 * transformed multimap.
	 *
	 * @since 7.0
	 */
	public static <K, V1, V2> ListMultimap<K, V2> transformEntries(ListMultimap<K, V1> fromMap,
			EntryTransformer<? super K, ? super V1, V2> transformer) {
		return new TransformedEntriesListMultimap<K, V1, V2>(fromMap, transformer);
	}

	private static final class TransformedEntriesListMultimap<K, V1, V2> extends TransformedEntriesMultimap<K, V1, V2>
			implements ListMultimap<K, V2> {

		TransformedEntriesListMultimap(ListMultimap<K, V1> fromMultimap,
				EntryTransformer<? super K, ? super V1, V2> transformer) {
			super(fromMultimap, transformer);
		}

		@Override
		List<V2> transform(K key, Collection<V1> values) {
			return Lists.transform((List<V1>) values, Maps.asValueToValueFunction(transformer, key));
		}

		@Override
		public List<V2> get(K key) {
			return transform(key, fromMultimap.get(key));
		}

		@SuppressWarnings("unchecked")
		@Override
		public List<V2> removeAll(Object key) {
			return transform((K) key, fromMultimap.removeAll(key));
		}

		@Override
		public List<V2> replaceValues(K key, Iterable<? extends V2> values) {
			throw new UnsupportedOperationException();
		}
	}

	/**
	 * Creates an index {@code ImmutableListMultimap} that contains the results of
	 * applying a specified function to each item in an {@code Iterable} of values.
	 * Each value will be stored as a value in the resulting multimap, yielding a
	 * multimap with the same size as the input iterable. The key used to store that
	 * value in the multimap will be the result of calling the function on that
	 * value. The resulting multimap is created as an immutable snapshot. In the
	 * returned multimap, keys appear in the order they are first encountered, and
	 * the values corresponding to each key appear in the same order as they are
	 * encountered.
	 *
	 * <p>
	 * For example,
	 * 
	 * <pre>
	 *    {@code
	 *
	 *   List<String> badGuys =
	 *       Arrays.asList("Inky", "Blinky", "Pinky", "Pinky", "Clyde");
	 *   Function<String, Integer> stringLengthFunction = ...;
	 *   Multimap<Integer, String> index =
	 *       Multimaps.index(badGuys, stringLengthFunction);
	 *   System.out.println(index);}
	 * </pre>
	 *
	 * <p>
	 * prints
	 * 
	 * <pre>
	 *    {@code
	 *
	 *   {4=[Inky], 6=[Blinky], 5=[Pinky, Pinky, Clyde]}}
	 * </pre>
	 *
	 * <p>
	 * The returned multimap is serializable if its keys and values are all
	 * serializable.
	 *
	 * @param values      the values to use when constructing the {@code
	 *     ImmutableListMultimap}
	 * @param keyFunction the function used to produce the key for each value
	 * @return {@code ImmutableListMultimap} mapping the result of evaluating the
	 *         function {@code keyFunction} on each value in the input collection to
	 *         that value
	 * @throws NullPointerException if any of the following cases is true:
	 *                              <ul>
	 *                              <li>{@code values} is null
	 *                              <li>{@code keyFunction} is null
	 *                              <li>An element in {@code values} is null
	 *                              <li>{@code keyFunction} returns {@code null} for
	 *                              any element of {@code
	 *         values}
	 *                              </ul>
	 */
	public static <K, V> ImmutableListMultimap<K, V> index(Iterable<V> values, Function<? super V, K> keyFunction) {
		return index(values.iterator(), keyFunction);
	}

	/**
	 * Creates an index {@code ImmutableListMultimap} that contains the results of
	 * applying a specified function to each item in an {@code Iterator} of values.
	 * Each value will be stored as a value in the resulting multimap, yielding a
	 * multimap with the same size as the input iterator. The key used to store that
	 * value in the multimap will be the result of calling the function on that
	 * value. The resulting multimap is created as an immutable snapshot. In the
	 * returned multimap, keys appear in the order they are first encountered, and
	 * the values corresponding to each key appear in the same order as they are
	 * encountered.
	 *
	 * <p>
	 * For example,
	 * 
	 * <pre>
	 *    {@code
	 *
	 *   List<String> badGuys =
	 *       Arrays.asList("Inky", "Blinky", "Pinky", "Pinky", "Clyde");
	 *   Function<String, Integer> stringLengthFunction = ...;
	 *   Multimap<Integer, String> index =
	 *       Multimaps.index(badGuys.iterator(), stringLengthFunction);
	 *   System.out.println(index);}
	 * </pre>
	 *
	 * <p>
	 * prints
	 * 
	 * <pre>
	 *    {@code
	 *
	 *   {4=[Inky], 6=[Blinky], 5=[Pinky, Pinky, Clyde]}}
	 * </pre>
	 *
	 * <p>
	 * The returned multimap is serializable if its keys and values are all
	 * serializable.
	 *
	 * @param values      the values to use when constructing the {@code
	 *     ImmutableListMultimap}
	 * @param keyFunction the function used to produce the key for each value
	 * @return {@code ImmutableListMultimap} mapping the result of evaluating the
	 *         function {@code keyFunction} on each value in the input collection to
	 *         that value
	 * @throws NullPointerException if any of the following cases is true:
	 *                              <ul>
	 *                              <li>{@code values} is null
	 *                              <li>{@code keyFunction} is null
	 *                              <li>An element in {@code values} is null
	 *                              <li>{@code keyFunction} returns {@code null} for
	 *                              any element of {@code
	 *         values}
	 *                              </ul>
	 * @since 10.0
	 */
	public static <K, V> ImmutableListMultimap<K, V> index(Iterator<V> values, Function<? super V, K> keyFunction) {
		checkNotNull(keyFunction);
		ImmutableListMultimap.Builder<K, V> builder = ImmutableListMultimap.builder();
		while (values.hasNext()) {
			V value = values.next();
			checkNotNull(value, values);
			builder.put(keyFunction.apply(value), value);
		}
		return builder.build();
	}

	static class Keys<K, V> extends AbstractMultiset<K> {
		final Multimap<K, V> multimap;

		Keys(Multimap<K, V> multimap) {
			this.multimap = multimap;
		}

		@Override
		Iterator<Multiset.Entry<K>> entryIterator() {
			return new TransformedIterator<Map.Entry<K, Collection<V>>, Multiset.Entry<K>>(
					multimap.asMap().entrySet().iterator()) {
				@Override
				Multiset.Entry<K> transform(final Map.Entry<K, Collection<V>> backingEntry) {
					return new Multisets.AbstractEntry<K>() {
						@Override
						public K getElement() {
							return backingEntry.getKey();
						}

						@Override
						public int getCount() {
							return backingEntry.getValue().size();
						}
					};
				}
			};
		}

		@Override
		int distinctElements() {
			return multimap.asMap().size();
		}

		@Override
		Set<Multiset.Entry<K>> createEntrySet() {
			return new KeysEntrySet();
		}

		class KeysEntrySet extends Multisets.EntrySet<K> {
			@Override
			Multiset<K> multiset() {
				return Keys.this;
			}

			@Override
			public Iterator<Multiset.Entry<K>> iterator() {
				return entryIterator();
			}

			@Override
			public int size() {
				return distinctElements();
			}

			@Override
			public boolean isEmpty() {
				return multimap.isEmpty();
			}

			@Override
			public boolean contains(@Nullable Object o) {
				if (o instanceof Multiset.Entry) {
					Multiset.Entry<?> entry = (Multiset.Entry<?>) o;
					Collection<V> collection = multimap.asMap().get(entry.getElement());
					return collection != null && collection.size() == entry.getCount();
				}
				return false;
			}

			@Override
			public boolean remove(@Nullable Object o) {
				if (o instanceof Multiset.Entry) {
					Multiset.Entry<?> entry = (Multiset.Entry<?>) o;
					Collection<V> collection = multimap.asMap().get(entry.getElement());
					if (collection != null && collection.size() == entry.getCount()) {
						collection.clear();
						return true;
					}
				}
				return false;
			}
		}

		@Override
		public boolean contains(@Nullable Object element) {
			return multimap.containsKey(element);
		}

		@Override
		public Iterator<K> iterator() {
			return Maps.keyIterator(multimap.entries().iterator());
		}

		@Override
		public int count(@Nullable Object element) {
			Collection<V> values = Maps.safeGet(multimap.asMap(), element);
			return (values == null) ? 0 : values.size();
		}

		@Override
		public int remove(@Nullable Object element, int occurrences) {
			checkNonnegative(occurrences, "occurrences");
			if (occurrences == 0) {
				return count(element);
			}

			Collection<V> values = Maps.safeGet(multimap.asMap(), element);

			if (values == null) {
				return 0;
			}

			int oldCount = values.size();
			if (occurrences >= oldCount) {
				values.clear();
			} else {
				Iterator<V> iterator = values.iterator();
				for (int i = 0; i < occurrences; i++) {
					iterator.next();
					iterator.remove();
				}
			}
			return oldCount;
		}

		@Override
		public void clear() {
			multimap.clear();
		}

		@Override
		public Set<K> elementSet() {
			return multimap.keySet();
		}
	}

	/**
	 * A skeleton implementation of {@link Multimap#entries()}.
	 */
	abstract static class Entries<K, V> extends AbstractCollection<Map.Entry<K, V>> {
		abstract Multimap<K, V> multimap();

		@Override
		public int size() {
			return multimap().size();
		}

		@Override
		public boolean contains(@Nullable Object o) {
			if (o instanceof Map.Entry) {
				Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o;
				return multimap().containsEntry(entry.getKey(), entry.getValue());
			}
			return false;
		}

		@Override
		public boolean remove(@Nullable Object o) {
			if (o instanceof Map.Entry) {
				Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o;
				return multimap().remove(entry.getKey(), entry.getValue());
			}
			return false;
		}

		@Override
		public void clear() {
			multimap().clear();
		}
	}

	/**
	 * A skeleton implementation of {@link Multimap#asMap()}.
	 */
	static final class AsMap<K, V> extends Maps.ImprovedAbstractMap<K, Collection<V>> {
		private final Multimap<K, V> multimap;

		AsMap(Multimap<K, V> multimap) {
			this.multimap = checkNotNull(multimap);
		}

		@Override
		public int size() {
			return multimap.keySet().size();
		}

		@Override
		protected Set<Entry<K, Collection<V>>> createEntrySet() {
			return new EntrySet();
		}

		void removeValuesForKey(Object key) {
			multimap.keySet().remove(key);
		}

		class EntrySet extends Maps.EntrySet<K, Collection<V>> {
			@Override
			Map<K, Collection<V>> map() {
				return AsMap.this;
			}

			@Override
			public Iterator<Entry<K, Collection<V>>> iterator() {
				return Maps.asMapEntryIterator(multimap.keySet(), new Function<K, Collection<V>>() {
					@Override
					public Collection<V> apply(K key) {
						return multimap.get(key);
					}
				});
			}

			@Override
			public boolean remove(Object o) {
				if (!contains(o)) {
					return false;
				}
				Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o;
				removeValuesForKey(entry.getKey());
				return true;
			}
		}

		@SuppressWarnings("unchecked")
		@Override
		public Collection<V> get(Object key) {
			return containsKey(key) ? multimap.get((K) key) : null;
		}

		@Override
		public Collection<V> remove(Object key) {
			return containsKey(key) ? multimap.removeAll(key) : null;
		}

		@Override
		public Set<K> keySet() {
			return multimap.keySet();
		}

		@Override
		public boolean isEmpty() {
			return multimap.isEmpty();
		}

		@Override
		public boolean containsKey(Object key) {
			return multimap.containsKey(key);
		}

		@Override
		public void clear() {
			multimap.clear();
		}
	}

	/**
	 * Returns a multimap containing the mappings in {@code unfiltered} whose keys
	 * satisfy a predicate. The returned multimap is a live view of
	 * {@code unfiltered}; changes to one affect the other.
	 *
	 * <p>
	 * The resulting multimap's views have iterators that don't support
	 * {@code remove()}, but all other methods are supported by the multimap and its
	 * views. When adding a key that doesn't satisfy the predicate, the multimap's
	 * {@code put()}, {@code putAll()}, and {@code replaceValues()} methods throw an
	 * {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered multimap or its views, only mappings whose keys satisfy the
	 * filter will be removed from the underlying multimap.
	 *
	 * <p>
	 * The returned multimap isn't threadsafe or serializable, even if
	 * {@code unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered multimap's methods, such as {@code size()}, iterate
	 * across every key/value mapping in the underlying multimap and determine which
	 * satisfy the filter. When a live view is <i>not</i> needed, it may be faster
	 * to copy the filtered multimap and use the copy.
	 *
	 * <p>
	 * <b>Warning:</b> {@code keyPredicate} must be <i>consistent with equals</i>,
	 * as documented at {@link Predicate#apply}. Do not provide a predicate such as
	 * {@code Predicates.instanceOf(ArrayList.class)}, which is inconsistent with
	 * equals.
	 *
	 * @since 11.0
	 */
	public static <K, V> Multimap<K, V> filterKeys(Multimap<K, V> unfiltered, final Predicate<? super K> keyPredicate) {
		if (unfiltered instanceof SetMultimap) {
			return filterKeys((SetMultimap<K, V>) unfiltered, keyPredicate);
		} else if (unfiltered instanceof ListMultimap) {
			return filterKeys((ListMultimap<K, V>) unfiltered, keyPredicate);
		} else if (unfiltered instanceof FilteredKeyMultimap) {
			FilteredKeyMultimap<K, V> prev = (FilteredKeyMultimap<K, V>) unfiltered;
			return new FilteredKeyMultimap<K, V>(prev.unfiltered, Predicates.and(prev.keyPredicate, keyPredicate));
		} else if (unfiltered instanceof FilteredMultimap) {
			FilteredMultimap<K, V> prev = (FilteredMultimap<K, V>) unfiltered;
			return filterFiltered(prev, Maps.<K>keyPredicateOnEntries(keyPredicate));
		} else {
			return new FilteredKeyMultimap<K, V>(unfiltered, keyPredicate);
		}
	}

	/**
	 * Returns a multimap containing the mappings in {@code unfiltered} whose keys
	 * satisfy a predicate. The returned multimap is a live view of
	 * {@code unfiltered}; changes to one affect the other.
	 *
	 * <p>
	 * The resulting multimap's views have iterators that don't support
	 * {@code remove()}, but all other methods are supported by the multimap and its
	 * views. When adding a key that doesn't satisfy the predicate, the multimap's
	 * {@code put()}, {@code putAll()}, and {@code replaceValues()} methods throw an
	 * {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered multimap or its views, only mappings whose keys satisfy the
	 * filter will be removed from the underlying multimap.
	 *
	 * <p>
	 * The returned multimap isn't threadsafe or serializable, even if
	 * {@code unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered multimap's methods, such as {@code size()}, iterate
	 * across every key/value mapping in the underlying multimap and determine which
	 * satisfy the filter. When a live view is <i>not</i> needed, it may be faster
	 * to copy the filtered multimap and use the copy.
	 *
	 * <p>
	 * <b>Warning:</b> {@code keyPredicate} must be <i>consistent with equals</i>,
	 * as documented at {@link Predicate#apply}. Do not provide a predicate such as
	 * {@code Predicates.instanceOf(ArrayList.class)}, which is inconsistent with
	 * equals.
	 *
	 * @since 14.0
	 */
	public static <K, V> SetMultimap<K, V> filterKeys(SetMultimap<K, V> unfiltered,
			final Predicate<? super K> keyPredicate) {
		if (unfiltered instanceof FilteredKeySetMultimap) {
			FilteredKeySetMultimap<K, V> prev = (FilteredKeySetMultimap<K, V>) unfiltered;
			return new FilteredKeySetMultimap<K, V>(prev.unfiltered(), Predicates.and(prev.keyPredicate, keyPredicate));
		} else if (unfiltered instanceof FilteredSetMultimap) {
			FilteredSetMultimap<K, V> prev = (FilteredSetMultimap<K, V>) unfiltered;
			return filterFiltered(prev, Maps.<K>keyPredicateOnEntries(keyPredicate));
		} else {
			return new FilteredKeySetMultimap<K, V>(unfiltered, keyPredicate);
		}
	}

	/**
	 * Returns a multimap containing the mappings in {@code unfiltered} whose keys
	 * satisfy a predicate. The returned multimap is a live view of
	 * {@code unfiltered}; changes to one affect the other.
	 *
	 * <p>
	 * The resulting multimap's views have iterators that don't support
	 * {@code remove()}, but all other methods are supported by the multimap and its
	 * views. When adding a key that doesn't satisfy the predicate, the multimap's
	 * {@code put()}, {@code putAll()}, and {@code replaceValues()} methods throw an
	 * {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered multimap or its views, only mappings whose keys satisfy the
	 * filter will be removed from the underlying multimap.
	 *
	 * <p>
	 * The returned multimap isn't threadsafe or serializable, even if
	 * {@code unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered multimap's methods, such as {@code size()}, iterate
	 * across every key/value mapping in the underlying multimap and determine which
	 * satisfy the filter. When a live view is <i>not</i> needed, it may be faster
	 * to copy the filtered multimap and use the copy.
	 *
	 * <p>
	 * <b>Warning:</b> {@code keyPredicate} must be <i>consistent with equals</i>,
	 * as documented at {@link Predicate#apply}. Do not provide a predicate such as
	 * {@code Predicates.instanceOf(ArrayList.class)}, which is inconsistent with
	 * equals.
	 *
	 * @since 14.0
	 */
	public static <K, V> ListMultimap<K, V> filterKeys(ListMultimap<K, V> unfiltered,
			final Predicate<? super K> keyPredicate) {
		if (unfiltered instanceof FilteredKeyListMultimap) {
			FilteredKeyListMultimap<K, V> prev = (FilteredKeyListMultimap<K, V>) unfiltered;
			return new FilteredKeyListMultimap<K, V>(prev.unfiltered(),
					Predicates.and(prev.keyPredicate, keyPredicate));
		} else {
			return new FilteredKeyListMultimap<K, V>(unfiltered, keyPredicate);
		}
	}

	/**
	 * Returns a multimap containing the mappings in {@code unfiltered} whose values
	 * satisfy a predicate. The returned multimap is a live view of
	 * {@code unfiltered}; changes to one affect the other.
	 *
	 * <p>
	 * The resulting multimap's views have iterators that don't support
	 * {@code remove()}, but all other methods are supported by the multimap and its
	 * views. When adding a value that doesn't satisfy the predicate, the multimap's
	 * {@code put()}, {@code putAll()}, and {@code replaceValues()} methods throw an
	 * {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered multimap or its views, only mappings whose value satisfy the
	 * filter will be removed from the underlying multimap.
	 *
	 * <p>
	 * The returned multimap isn't threadsafe or serializable, even if
	 * {@code unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered multimap's methods, such as {@code size()}, iterate
	 * across every key/value mapping in the underlying multimap and determine which
	 * satisfy the filter. When a live view is <i>not</i> needed, it may be faster
	 * to copy the filtered multimap and use the copy.
	 *
	 * <p>
	 * <b>Warning:</b> {@code valuePredicate} must be <i>consistent with equals</i>,
	 * as documented at {@link Predicate#apply}. Do not provide a predicate such as
	 * {@code Predicates.instanceOf(ArrayList.class)}, which is inconsistent with
	 * equals.
	 *
	 * @since 11.0
	 */
	public static <K, V> Multimap<K, V> filterValues(Multimap<K, V> unfiltered,
			final Predicate<? super V> valuePredicate) {
		return filterEntries(unfiltered, Maps.<V>valuePredicateOnEntries(valuePredicate));
	}

	/**
	 * Returns a multimap containing the mappings in {@code unfiltered} whose values
	 * satisfy a predicate. The returned multimap is a live view of
	 * {@code unfiltered}; changes to one affect the other.
	 *
	 * <p>
	 * The resulting multimap's views have iterators that don't support
	 * {@code remove()}, but all other methods are supported by the multimap and its
	 * views. When adding a value that doesn't satisfy the predicate, the multimap's
	 * {@code put()}, {@code putAll()}, and {@code replaceValues()} methods throw an
	 * {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered multimap or its views, only mappings whose value satisfy the
	 * filter will be removed from the underlying multimap.
	 *
	 * <p>
	 * The returned multimap isn't threadsafe or serializable, even if
	 * {@code unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered multimap's methods, such as {@code size()}, iterate
	 * across every key/value mapping in the underlying multimap and determine which
	 * satisfy the filter. When a live view is <i>not</i> needed, it may be faster
	 * to copy the filtered multimap and use the copy.
	 *
	 * <p>
	 * <b>Warning:</b> {@code valuePredicate} must be <i>consistent with equals</i>,
	 * as documented at {@link Predicate#apply}. Do not provide a predicate such as
	 * {@code Predicates.instanceOf(ArrayList.class)}, which is inconsistent with
	 * equals.
	 *
	 * @since 14.0
	 */
	public static <K, V> SetMultimap<K, V> filterValues(SetMultimap<K, V> unfiltered,
			final Predicate<? super V> valuePredicate) {
		return filterEntries(unfiltered, Maps.<V>valuePredicateOnEntries(valuePredicate));
	}

	/**
	 * Returns a multimap containing the mappings in {@code unfiltered} that satisfy
	 * a predicate. The returned multimap is a live view of {@code unfiltered};
	 * changes to one affect the other.
	 *
	 * <p>
	 * The resulting multimap's views have iterators that don't support
	 * {@code remove()}, but all other methods are supported by the multimap and its
	 * views. When adding a key/value pair that doesn't satisfy the predicate,
	 * multimap's {@code put()}, {@code putAll()}, and {@code replaceValues()}
	 * methods throw an {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered multimap or its views, only mappings whose keys satisfy the
	 * filter will be removed from the underlying multimap.
	 *
	 * <p>
	 * The returned multimap isn't threadsafe or serializable, even if
	 * {@code unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered multimap's methods, such as {@code size()}, iterate
	 * across every key/value mapping in the underlying multimap and determine which
	 * satisfy the filter. When a live view is <i>not</i> needed, it may be faster
	 * to copy the filtered multimap and use the copy.
	 *
	 * <p>
	 * <b>Warning:</b> {@code entryPredicate} must be <i>consistent with equals</i>,
	 * as documented at {@link Predicate#apply}.
	 *
	 * @since 11.0
	 */
	public static <K, V> Multimap<K, V> filterEntries(Multimap<K, V> unfiltered,
			Predicate<? super Entry<K, V>> entryPredicate) {
		checkNotNull(entryPredicate);
		if (unfiltered instanceof SetMultimap) {
			return filterEntries((SetMultimap<K, V>) unfiltered, entryPredicate);
		}
		return (unfiltered instanceof FilteredMultimap)
				? filterFiltered((FilteredMultimap<K, V>) unfiltered, entryPredicate)
				: new FilteredEntryMultimap<K, V>(checkNotNull(unfiltered), entryPredicate);
	}

	/**
	 * Returns a multimap containing the mappings in {@code unfiltered} that satisfy
	 * a predicate. The returned multimap is a live view of {@code unfiltered};
	 * changes to one affect the other.
	 *
	 * <p>
	 * The resulting multimap's views have iterators that don't support
	 * {@code remove()}, but all other methods are supported by the multimap and its
	 * views. When adding a key/value pair that doesn't satisfy the predicate,
	 * multimap's {@code put()}, {@code putAll()}, and {@code replaceValues()}
	 * methods throw an {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered multimap or its views, only mappings whose keys satisfy the
	 * filter will be removed from the underlying multimap.
	 *
	 * <p>
	 * The returned multimap isn't threadsafe or serializable, even if
	 * {@code unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered multimap's methods, such as {@code size()}, iterate
	 * across every key/value mapping in the underlying multimap and determine which
	 * satisfy the filter. When a live view is <i>not</i> needed, it may be faster
	 * to copy the filtered multimap and use the copy.
	 *
	 * <p>
	 * <b>Warning:</b> {@code entryPredicate} must be <i>consistent with equals</i>,
	 * as documented at {@link Predicate#apply}.
	 *
	 * @since 14.0
	 */
	public static <K, V> SetMultimap<K, V> filterEntries(SetMultimap<K, V> unfiltered,
			Predicate<? super Entry<K, V>> entryPredicate) {
		checkNotNull(entryPredicate);
		return (unfiltered instanceof FilteredSetMultimap)
				? filterFiltered((FilteredSetMultimap<K, V>) unfiltered, entryPredicate)
				: new FilteredEntrySetMultimap<K, V>(checkNotNull(unfiltered), entryPredicate);
	}

	/**
	 * Support removal operations when filtering a filtered multimap. Since a
	 * filtered multimap has iterators that don't support remove, passing one to the
	 * FilteredEntryMultimap constructor would lead to a multimap whose removal
	 * operations would fail. This method combines the predicates to avoid that
	 * problem.
	 */
	private static <K, V> Multimap<K, V> filterFiltered(FilteredMultimap<K, V> multimap,
			Predicate<? super Entry<K, V>> entryPredicate) {
		Predicate<Entry<K, V>> predicate = Predicates.and(multimap.entryPredicate(), entryPredicate);
		return new FilteredEntryMultimap<K, V>(multimap.unfiltered(), predicate);
	}

	/**
	 * Support removal operations when filtering a filtered multimap. Since a
	 * filtered multimap has iterators that don't support remove, passing one to the
	 * FilteredEntryMultimap constructor would lead to a multimap whose removal
	 * operations would fail. This method combines the predicates to avoid that
	 * problem.
	 */
	private static <K, V> SetMultimap<K, V> filterFiltered(FilteredSetMultimap<K, V> multimap,
			Predicate<? super Entry<K, V>> entryPredicate) {
		Predicate<Entry<K, V>> predicate = Predicates.and(multimap.entryPredicate(), entryPredicate);
		return new FilteredEntrySetMultimap<K, V>(multimap.unfiltered(), predicate);
	}

	static boolean equalsImpl(Multimap<?, ?> multimap, @Nullable Object object) {
		if (object == multimap) {
			return true;
		}
		if (object instanceof Multimap) {
			Multimap<?, ?> that = (Multimap<?, ?>) object;
			return multimap.asMap().equals(that.asMap());
		}
		return false;
	}

	// TODO(jlevy): Create methods that filter a SortedSetMultimap.
}