/*
 * 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.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Predicates.compose;
import static com.google.common.base.Predicates.equalTo;
import static com.google.common.base.Predicates.in;
import static com.google.common.base.Predicates.not;
import static com.google.common.collect.CollectPreconditions.checkNonnegative;

import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.EnumMap;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NavigableMap;
import java.util.NavigableSet;
import java.util.Properties;
import java.util.Set;
import java.util.SortedMap;
import java.util.SortedSet;
import java.util.TreeMap;

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.Converter;
import com.google.common.base.Equivalence;
import com.google.common.base.Function;
import com.google.common.base.Joiner.MapJoiner;
import com.google.common.base.Objects;
import com.google.common.base.Preconditions;
import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import com.google.common.collect.MapDifference.ValueDifference;
import com.google.common.primitives.Ints;

/**
 * Static utility methods pertaining to {@link Map} instances (including
 * instances of {@link SortedMap}, {@link BiMap}, etc.). Also see this class's
 * counterparts {@link Lists}, {@link Sets} and {@link Queues}.
 *
 * <p>
 * See the Guava User Guide article on <a href=
 * "http://code.google.com/p/guava-libraries/wiki/CollectionUtilitiesExplained#Maps">
 * {@code Maps}</a>.
 *
 * @author Kevin Bourrillion
 * @author Mike Bostock
 * @author Isaac Shum
 * @author Louis Wasserman
 * @since 2.0 (imported from Google Collections Library)
 */
@GwtCompatible(emulated = true)
public final class Maps {
	private Maps() {
	}

	private enum EntryFunction implements Function<Entry<?, ?>, Object> {
		KEY {
			@Override
			@Nullable
			public Object apply(Entry<?, ?> entry) {
				return entry.getKey();
			}
		},
		VALUE {
			@Override
			@Nullable
			public Object apply(Entry<?, ?> entry) {
				return entry.getValue();
			}
		};
	}

	@SuppressWarnings("unchecked")
	static <K> Function<Entry<K, ?>, K> keyFunction() {
		return (Function) EntryFunction.KEY;
	}

	@SuppressWarnings("unchecked")
	static <V> Function<Entry<?, V>, V> valueFunction() {
		return (Function) EntryFunction.VALUE;
	}

	static <K, V> Iterator<K> keyIterator(Iterator<Entry<K, V>> entryIterator) {
		return Iterators.transform(entryIterator, Maps.<K>keyFunction());
	}

	static <K, V> Iterator<V> valueIterator(Iterator<Entry<K, V>> entryIterator) {
		return Iterators.transform(entryIterator, Maps.<V>valueFunction());
	}

	static <K, V> UnmodifiableIterator<V> valueIterator(final UnmodifiableIterator<Entry<K, V>> entryIterator) {
		return new UnmodifiableIterator<V>() {
			@Override
			public boolean hasNext() {
				return entryIterator.hasNext();
			}

			@Override
			public V next() {
				return entryIterator.next().getValue();
			}
		};
	}

	/**
	 * Returns an immutable map instance containing the given entries. Internally,
	 * the returned map will be backed by an {@link EnumMap}.
	 *
	 * <p>
	 * The iteration order of the returned map follows the enum's iteration order,
	 * not the order in which the elements appear in the given map.
	 *
	 * @param map the map to make an immutable copy of
	 * @return an immutable map containing those entries
	 * @since 14.0
	 */
	@GwtCompatible(serializable = true)
	@Beta
	public static <K extends Enum<K>, V> ImmutableMap<K, V> immutableEnumMap(Map<K, ? extends V> map) {
		if (map instanceof ImmutableEnumMap) {
			@SuppressWarnings("unchecked") // safe covariant cast
			ImmutableEnumMap<K, V> result = (ImmutableEnumMap<K, V>) map;
			return result;
		} else if (map.isEmpty()) {
			return ImmutableMap.of();
		} else {
			for (Map.Entry<K, ? extends V> entry : map.entrySet()) {
				checkNotNull(entry.getKey());
				checkNotNull(entry.getValue());
			}
			return ImmutableEnumMap.asImmutable(new EnumMap<K, V>(map));
		}
	}

	/**
	 * Creates a <i>mutable</i>, empty {@code HashMap} instance.
	 *
	 * <p>
	 * <b>Note:</b> if mutability is not required, use {@link ImmutableMap#of()}
	 * instead.
	 *
	 * <p>
	 * <b>Note:</b> if {@code K} is an {@code enum} type, use {@link #newEnumMap}
	 * instead.
	 *
	 * @return a new, empty {@code HashMap}
	 */
	public static <K, V> HashMap<K, V> newHashMap() {
		return new HashMap<K, V>();
	}

	/**
	 * Creates a {@code HashMap} instance, with a high enough "initial capacity"
	 * that it <i>should</i> hold {@code expectedSize} elements without growth. This
	 * behavior cannot be broadly guaranteed, but it is observed to be true for
	 * OpenJDK 1.6. It also can't be guaranteed that the method isn't inadvertently
	 * <i>oversizing</i> the returned map.
	 *
	 * @param expectedSize the number of elements you expect to add to the returned
	 *                     map
	 * @return a new, empty {@code HashMap} with enough capacity to hold {@code
	 *         expectedSize} elements without resizing
	 * @throws IllegalArgumentException if {@code expectedSize} is negative
	 */
	public static <K, V> HashMap<K, V> newHashMapWithExpectedSize(int expectedSize) {
		return new HashMap<K, V>(capacity(expectedSize));
	}

	/**
	 * Returns a capacity that is sufficient to keep the map from being resized as
	 * long as it grows no larger than expectedSize and the load factor is >= its
	 * default (0.75).
	 */
	static int capacity(int expectedSize) {
		if (expectedSize < 3) {
			checkNonnegative(expectedSize, "expectedSize");
			return expectedSize + 1;
		}
		if (expectedSize < Ints.MAX_POWER_OF_TWO) {
			return expectedSize + expectedSize / 3;
		}
		return Integer.MAX_VALUE; // any large value
	}

	/**
	 * Creates a <i>mutable</i> {@code HashMap} instance with the same mappings as
	 * the specified map.
	 *
	 * <p>
	 * <b>Note:</b> if mutability is not required, use
	 * {@link ImmutableMap#copyOf(Map)} instead.
	 *
	 * <p>
	 * <b>Note:</b> if {@code K} is an {@link Enum} type, use {@link #newEnumMap}
	 * instead.
	 *
	 * @param map the mappings to be placed in the new map
	 * @return a new {@code HashMap} initialized with the mappings from {@code
	 *         map}
	 */
	public static <K, V> HashMap<K, V> newHashMap(Map<? extends K, ? extends V> map) {
		return new HashMap<K, V>(map);
	}

	/**
	 * Creates a <i>mutable</i>, empty, insertion-ordered {@code LinkedHashMap}
	 * instance.
	 *
	 * <p>
	 * <b>Note:</b> if mutability is not required, use {@link ImmutableMap#of()}
	 * instead.
	 *
	 * @return a new, empty {@code LinkedHashMap}
	 */
	public static <K, V> LinkedHashMap<K, V> newLinkedHashMap() {
		return new LinkedHashMap<K, V>();
	}

	/**
	 * Creates a <i>mutable</i>, insertion-ordered {@code LinkedHashMap} instance
	 * with the same mappings as the specified map.
	 *
	 * <p>
	 * <b>Note:</b> if mutability is not required, use
	 * {@link ImmutableMap#copyOf(Map)} instead.
	 *
	 * @param map the mappings to be placed in the new map
	 * @return a new, {@code LinkedHashMap} initialized with the mappings from
	 *         {@code map}
	 */
	public static <K, V> LinkedHashMap<K, V> newLinkedHashMap(Map<? extends K, ? extends V> map) {
		return new LinkedHashMap<K, V>(map);
	}

	/**
	 * Creates a <i>mutable</i>, empty {@code TreeMap} instance using the natural
	 * ordering of its elements.
	 *
	 * <p>
	 * <b>Note:</b> if mutability is not required, use
	 * {@link ImmutableSortedMap#of()} instead.
	 *
	 * @return a new, empty {@code TreeMap}
	 */
	public static <K extends Comparable, V> TreeMap<K, V> newTreeMap() {
		return new TreeMap<K, V>();
	}

	/**
	 * Creates a <i>mutable</i> {@code TreeMap} instance with the same mappings as
	 * the specified map and using the same ordering as the specified map.
	 *
	 * <p>
	 * <b>Note:</b> if mutability is not required, use
	 * {@link ImmutableSortedMap#copyOfSorted(SortedMap)} instead.
	 *
	 * @param map the sorted map whose mappings are to be placed in the new map and
	 *            whose comparator is to be used to sort the new map
	 * @return a new {@code TreeMap} initialized with the mappings from {@code
	 *         map} and using the comparator of {@code map}
	 */
	public static <K, V> TreeMap<K, V> newTreeMap(SortedMap<K, ? extends V> map) {
		return new TreeMap<K, V>(map);
	}

	/**
	 * Creates a <i>mutable</i>, empty {@code TreeMap} instance using the given
	 * comparator.
	 *
	 * <p>
	 * <b>Note:</b> if mutability is not required, use {@code
	 * ImmutableSortedMap.orderedBy(comparator).build()} instead.
	 *
	 * @param comparator the comparator to sort the keys with
	 * @return a new, empty {@code TreeMap}
	 */
	public static <C, K extends C, V> TreeMap<K, V> newTreeMap(@Nullable Comparator<C> comparator) {
		// Ideally, the extra type parameter "C" shouldn't be necessary. It is a
		// work-around of a compiler type inference quirk that prevents the
		// following code from being compiled:
		// Comparator<Class<?>> comparator = null;
		// Map<Class<? extends Throwable>, String> map = newTreeMap(comparator);
		return new TreeMap<K, V>(comparator);
	}

	/**
	 * Creates an {@code EnumMap} instance.
	 *
	 * @param type the key type for this map
	 * @return a new, empty {@code EnumMap}
	 */
	public static <K extends Enum<K>, V> EnumMap<K, V> newEnumMap(Class<K> type) {
		return new EnumMap<K, V>(checkNotNull(type));
	}

	/**
	 * Creates an {@code EnumMap} with the same mappings as the specified map.
	 *
	 * @param map the map from which to initialize this {@code EnumMap}
	 * @return a new {@code EnumMap} initialized with the mappings from {@code
	 *         map}
	 * @throws IllegalArgumentException if {@code m} is not an {@code EnumMap}
	 *                                  instance and contains no mappings
	 */
	public static <K extends Enum<K>, V> EnumMap<K, V> newEnumMap(Map<K, ? extends V> map) {
		return new EnumMap<K, V>(map);
	}

	/**
	 * Creates an {@code IdentityHashMap} instance.
	 *
	 * @return a new, empty {@code IdentityHashMap}
	 */
	public static <K, V> IdentityHashMap<K, V> newIdentityHashMap() {
		return new IdentityHashMap<K, V>();
	}

	/**
	 * Computes the difference between two maps. This difference is an immutable
	 * snapshot of the state of the maps at the time this method is called. It will
	 * never change, even if the maps change at a later time.
	 *
	 * <p>
	 * Since this method uses {@code HashMap} instances internally, the keys of the
	 * supplied maps must be well-behaved with respect to {@link Object#equals} and
	 * {@link Object#hashCode}.
	 *
	 * <p>
	 * <b>Note:</b>If you only need to know whether two maps have the same mappings,
	 * call {@code left.equals(right)} instead of this method.
	 *
	 * @param left  the map to treat as the "left" map for purposes of comparison
	 * @param right the map to treat as the "right" map for purposes of comparison
	 * @return the difference between the two maps
	 */
	@SuppressWarnings("unchecked")
	public static <K, V> MapDifference<K, V> difference(Map<? extends K, ? extends V> left,
			Map<? extends K, ? extends V> right) {
		if (left instanceof SortedMap) {
			SortedMap<K, ? extends V> sortedLeft = (SortedMap<K, ? extends V>) left;
			SortedMapDifference<K, V> result = difference(sortedLeft, right);
			return result;
		}
		return difference(left, right, Equivalence.equals());
	}

	/**
	 * Computes the difference between two maps. This difference is an immutable
	 * snapshot of the state of the maps at the time this method is called. It will
	 * never change, even if the maps change at a later time.
	 *
	 * <p>
	 * Values are compared using a provided equivalence, in the case of equality,
	 * the value on the 'left' is returned in the difference.
	 *
	 * <p>
	 * Since this method uses {@code HashMap} instances internally, the keys of the
	 * supplied maps must be well-behaved with respect to {@link Object#equals} and
	 * {@link Object#hashCode}.
	 *
	 * @param left             the map to treat as the "left" map for purposes of
	 *                         comparison
	 * @param right            the map to treat as the "right" map for purposes of
	 *                         comparison
	 * @param valueEquivalence the equivalence relationship to use to compare values
	 * @return the difference between the two maps
	 * @since 10.0
	 */
	@Beta
	public static <K, V> MapDifference<K, V> difference(Map<? extends K, ? extends V> left,
			Map<? extends K, ? extends V> right, Equivalence<? super V> valueEquivalence) {
		Preconditions.checkNotNull(valueEquivalence);

		Map<K, V> onlyOnLeft = newHashMap();
		Map<K, V> onlyOnRight = new HashMap<K, V>(right); // will whittle it down
		Map<K, V> onBoth = newHashMap();
		Map<K, MapDifference.ValueDifference<V>> differences = newHashMap();
		doDifference(left, right, valueEquivalence, onlyOnLeft, onlyOnRight, onBoth, differences);
		return new MapDifferenceImpl<K, V>(onlyOnLeft, onlyOnRight, onBoth, differences);
	}

	private static <K, V> void doDifference(Map<? extends K, ? extends V> left, Map<? extends K, ? extends V> right,
			Equivalence<? super V> valueEquivalence, Map<K, V> onlyOnLeft, Map<K, V> onlyOnRight, Map<K, V> onBoth,
			Map<K, MapDifference.ValueDifference<V>> differences) {
		for (Entry<? extends K, ? extends V> entry : left.entrySet()) {
			K leftKey = entry.getKey();
			V leftValue = entry.getValue();
			if (right.containsKey(leftKey)) {
				V rightValue = onlyOnRight.remove(leftKey);
				if (valueEquivalence.equivalent(leftValue, rightValue)) {
					onBoth.put(leftKey, leftValue);
				} else {
					differences.put(leftKey, ValueDifferenceImpl.create(leftValue, rightValue));
				}
			} else {
				onlyOnLeft.put(leftKey, leftValue);
			}
		}
	}

	private static <K, V> Map<K, V> unmodifiableMap(Map<K, V> map) {
		if (map instanceof SortedMap) {
			return Collections.unmodifiableSortedMap((SortedMap<K, ? extends V>) map);
		} else {
			return Collections.unmodifiableMap(map);
		}
	}

	static class MapDifferenceImpl<K, V> implements MapDifference<K, V> {
		final Map<K, V> onlyOnLeft;
		final Map<K, V> onlyOnRight;
		final Map<K, V> onBoth;
		final Map<K, ValueDifference<V>> differences;

		MapDifferenceImpl(Map<K, V> onlyOnLeft, Map<K, V> onlyOnRight, Map<K, V> onBoth,
				Map<K, ValueDifference<V>> differences) {
			this.onlyOnLeft = unmodifiableMap(onlyOnLeft);
			this.onlyOnRight = unmodifiableMap(onlyOnRight);
			this.onBoth = unmodifiableMap(onBoth);
			this.differences = unmodifiableMap(differences);
		}

		@Override
		public boolean areEqual() {
			return onlyOnLeft.isEmpty() && onlyOnRight.isEmpty() && differences.isEmpty();
		}

		@Override
		public Map<K, V> entriesOnlyOnLeft() {
			return onlyOnLeft;
		}

		@Override
		public Map<K, V> entriesOnlyOnRight() {
			return onlyOnRight;
		}

		@Override
		public Map<K, V> entriesInCommon() {
			return onBoth;
		}

		@Override
		public Map<K, ValueDifference<V>> entriesDiffering() {
			return differences;
		}

		@Override
		public boolean equals(Object object) {
			if (object == this) {
				return true;
			}
			if (object instanceof MapDifference) {
				MapDifference<?, ?> other = (MapDifference<?, ?>) object;
				return entriesOnlyOnLeft().equals(other.entriesOnlyOnLeft())
						&& entriesOnlyOnRight().equals(other.entriesOnlyOnRight())
						&& entriesInCommon().equals(other.entriesInCommon())
						&& entriesDiffering().equals(other.entriesDiffering());
			}
			return false;
		}

		@Override
		public int hashCode() {
			return Objects.hashCode(entriesOnlyOnLeft(), entriesOnlyOnRight(), entriesInCommon(), entriesDiffering());
		}

		@Override
		public String toString() {
			if (areEqual()) {
				return "equal";
			}

			StringBuilder result = new StringBuilder("not equal");
			if (!onlyOnLeft.isEmpty()) {
				result.append(": only on left=").append(onlyOnLeft);
			}
			if (!onlyOnRight.isEmpty()) {
				result.append(": only on right=").append(onlyOnRight);
			}
			if (!differences.isEmpty()) {
				result.append(": value differences=").append(differences);
			}
			return result.toString();
		}
	}

	static class ValueDifferenceImpl<V> implements MapDifference.ValueDifference<V> {
		private final V left;
		private final V right;

		static <V> ValueDifference<V> create(@Nullable V left, @Nullable V right) {
			return new ValueDifferenceImpl<V>(left, right);
		}

		private ValueDifferenceImpl(@Nullable V left, @Nullable V right) {
			this.left = left;
			this.right = right;
		}

		@Override
		public V leftValue() {
			return left;
		}

		@Override
		public V rightValue() {
			return right;
		}

		@Override
		public boolean equals(@Nullable Object object) {
			if (object instanceof MapDifference.ValueDifference) {
				MapDifference.ValueDifference<?> that = (MapDifference.ValueDifference<?>) object;
				return Objects.equal(this.left, that.leftValue()) && Objects.equal(this.right, that.rightValue());
			}
			return false;
		}

		@Override
		public int hashCode() {
			return Objects.hashCode(left, right);
		}

		@Override
		public String toString() {
			return "(" + left + ", " + right + ")";
		}
	}

	/**
	 * Computes the difference between two sorted maps, using the comparator of the
	 * left map, or {@code Ordering.natural()} if the left map uses the natural
	 * ordering of its elements. This difference is an immutable snapshot of the
	 * state of the maps at the time this method is called. It will never change,
	 * even if the maps change at a later time.
	 *
	 * <p>
	 * Since this method uses {@code TreeMap} instances internally, the keys of the
	 * right map must all compare as distinct according to the comparator of the
	 * left map.
	 *
	 * <p>
	 * <b>Note:</b>If you only need to know whether two sorted maps have the same
	 * mappings, call {@code left.equals(right)} instead of this method.
	 *
	 * @param left  the map to treat as the "left" map for purposes of comparison
	 * @param right the map to treat as the "right" map for purposes of comparison
	 * @return the difference between the two maps
	 * @since 11.0
	 */
	public static <K, V> SortedMapDifference<K, V> difference(SortedMap<K, ? extends V> left,
			Map<? extends K, ? extends V> right) {
		checkNotNull(left);
		checkNotNull(right);
		Comparator<? super K> comparator = orNaturalOrder(left.comparator());
		SortedMap<K, V> onlyOnLeft = Maps.newTreeMap(comparator);
		SortedMap<K, V> onlyOnRight = Maps.newTreeMap(comparator);
		onlyOnRight.putAll(right); // will whittle it down
		SortedMap<K, V> onBoth = Maps.newTreeMap(comparator);
		SortedMap<K, MapDifference.ValueDifference<V>> differences = Maps.newTreeMap(comparator);
		doDifference(left, right, Equivalence.equals(), onlyOnLeft, onlyOnRight, onBoth, differences);
		return new SortedMapDifferenceImpl<K, V>(onlyOnLeft, onlyOnRight, onBoth, differences);
	}

	static class SortedMapDifferenceImpl<K, V> extends MapDifferenceImpl<K, V> implements SortedMapDifference<K, V> {
		SortedMapDifferenceImpl(SortedMap<K, V> onlyOnLeft, SortedMap<K, V> onlyOnRight, SortedMap<K, V> onBoth,
				SortedMap<K, ValueDifference<V>> differences) {
			super(onlyOnLeft, onlyOnRight, onBoth, differences);
		}

		@Override
		public SortedMap<K, ValueDifference<V>> entriesDiffering() {
			return (SortedMap<K, ValueDifference<V>>) super.entriesDiffering();
		}

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

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

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

	/**
	 * Returns the specified comparator if not null; otherwise returns {@code
	 * Ordering.natural()}. This method is an abomination of generics; the only
	 * purpose of this method is to contain the ugly type-casting in one place.
	 */
	@SuppressWarnings("unchecked")
	static <E> Comparator<? super E> orNaturalOrder(@Nullable Comparator<? super E> comparator) {
		if (comparator != null) { // can't use ? : because of javac bug 5080917
			return comparator;
		}
		return (Comparator<E>) Ordering.natural();
	}

	/**
	 * Returns a live {@link Map} view whose keys are the contents of {@code set}
	 * and whose values are computed on demand using {@code function}. To get an
	 * immutable <i>copy</i> instead, use {@link #toMap(Iterable, Function)}.
	 *
	 * <p>
	 * Specifically, for each {@code k} in the backing set, the returned map has an
	 * entry mapping {@code k} to {@code function.apply(k)}. The {@code
	 * keySet}, {@code values}, and {@code entrySet} views of the returned map
	 * iterate in the same order as the backing set.
	 *
	 * <p>
	 * Modifications to the backing set are read through to the returned map. The
	 * returned map supports removal operations if the backing set does. Removal
	 * operations write through to the backing set. The returned map does not
	 * support put operations.
	 *
	 * <p>
	 * <b>Warning</b>: If the function rejects {@code null}, caution is required to
	 * make sure the set does not contain {@code null}, because the view cannot stop
	 * {@code null} from being added to the set.
	 *
	 * <p>
	 * <b>Warning:</b> This method assumes that for any instance {@code k} of key
	 * type {@code K}, {@code k.equals(k2)} implies that {@code k2} is also of type
	 * {@code K}. Using a key type for which this may not hold, such as
	 * {@code ArrayList}, may risk a {@code ClassCastException} when calling methods
	 * on the resulting map view.
	 *
	 * @since 14.0
	 */
	@Beta
	public static <K, V> Map<K, V> asMap(Set<K> set, Function<? super K, V> function) {
		if (set instanceof SortedSet) {
			return asMap((SortedSet<K>) set, function);
		} else {
			return new AsMapView<K, V>(set, function);
		}
	}

	/**
	 * Returns a view of the sorted set as a map, mapping keys from the set
	 * according to the specified function.
	 *
	 * <p>
	 * Specifically, for each {@code k} in the backing set, the returned map has an
	 * entry mapping {@code k} to {@code function.apply(k)}. The {@code
	 * keySet}, {@code values}, and {@code entrySet} views of the returned map
	 * iterate in the same order as the backing set.
	 *
	 * <p>
	 * Modifications to the backing set are read through to the returned map. The
	 * returned map supports removal operations if the backing set does. Removal
	 * operations write through to the backing set. The returned map does not
	 * support put operations.
	 *
	 * <p>
	 * <b>Warning</b>: If the function rejects {@code null}, caution is required to
	 * make sure the set does not contain {@code null}, because the view cannot stop
	 * {@code null} from being added to the set.
	 *
	 * <p>
	 * <b>Warning:</b> This method assumes that for any instance {@code k} of key
	 * type {@code K}, {@code k.equals(k2)} implies that {@code k2} is also of type
	 * {@code K}. Using a key type for which this may not hold, such as
	 * {@code ArrayList}, may risk a {@code ClassCastException} when calling methods
	 * on the resulting map view.
	 *
	 * @since 14.0
	 */
	@Beta
	public static <K, V> SortedMap<K, V> asMap(SortedSet<K> set, Function<? super K, V> function) {
		return Platform.mapsAsMapSortedSet(set, function);
	}

	static <K, V> SortedMap<K, V> asMapSortedIgnoreNavigable(SortedSet<K> set, Function<? super K, V> function) {
		return new SortedAsMapView<K, V>(set, function);
	}

	/**
	 * Returns a view of the navigable set as a map, mapping keys from the set
	 * according to the specified function.
	 *
	 * <p>
	 * Specifically, for each {@code k} in the backing set, the returned map has an
	 * entry mapping {@code k} to {@code function.apply(k)}. The {@code
	 * keySet}, {@code values}, and {@code entrySet} views of the returned map
	 * iterate in the same order as the backing set.
	 *
	 * <p>
	 * Modifications to the backing set are read through to the returned map. The
	 * returned map supports removal operations if the backing set does. Removal
	 * operations write through to the backing set. The returned map does not
	 * support put operations.
	 *
	 * <p>
	 * <b>Warning</b>: If the function rejects {@code null}, caution is required to
	 * make sure the set does not contain {@code null}, because the view cannot stop
	 * {@code null} from being added to the set.
	 *
	 * <p>
	 * <b>Warning:</b> This method assumes that for any instance {@code k} of key
	 * type {@code K}, {@code k.equals(k2)} implies that {@code k2} is also of type
	 * {@code K}. Using a key type for which this may not hold, such as
	 * {@code ArrayList}, may risk a {@code ClassCastException} when calling methods
	 * on the resulting map view.
	 *
	 * @since 14.0
	 */
	@Beta
	@GwtIncompatible("NavigableMap")
	public static <K, V> NavigableMap<K, V> asMap(NavigableSet<K> set, Function<? super K, V> function) {
		return new NavigableAsMapView<K, V>(set, function);
	}

	private static class AsMapView<K, V> extends ImprovedAbstractMap<K, V> {

		private final Set<K> set;
		final Function<? super K, V> function;

		Set<K> backingSet() {
			return set;
		}

		AsMapView(Set<K> set, Function<? super K, V> function) {
			this.set = checkNotNull(set);
			this.function = checkNotNull(function);
		}

		@Override
		public Set<K> createKeySet() {
			return removeOnlySet(backingSet());
		}

		@Override
		Collection<V> createValues() {
			return Collections2.transform(set, function);
		}

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

		@Override
		public boolean containsKey(@Nullable Object key) {
			return backingSet().contains(key);
		}

		@Override
		public V get(@Nullable Object key) {
			if (Collections2.safeContains(backingSet(), key)) {
				@SuppressWarnings("unchecked") // unsafe, but Javadoc warns about it
				K k = (K) key;
				return function.apply(k);
			} else {
				return null;
			}
		}

		@Override
		public V remove(@Nullable Object key) {
			if (backingSet().remove(key)) {
				@SuppressWarnings("unchecked") // unsafe, but Javadoc warns about it
				K k = (K) key;
				return function.apply(k);
			} else {
				return null;
			}
		}

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

		@Override
		protected Set<Entry<K, V>> createEntrySet() {
			return new EntrySet<K, V>() {
				@Override
				Map<K, V> map() {
					return AsMapView.this;
				}

				@Override
				public Iterator<Entry<K, V>> iterator() {
					return asMapEntryIterator(backingSet(), function);
				}
			};
		}
	}

	static <K, V> Iterator<Entry<K, V>> asMapEntryIterator(Set<K> set, final Function<? super K, V> function) {
		return new TransformedIterator<K, Entry<K, V>>(set.iterator()) {
			@Override
			Entry<K, V> transform(final K key) {
				return immutableEntry(key, function.apply(key));
			}
		};
	}

	private static class SortedAsMapView<K, V> extends AsMapView<K, V> implements SortedMap<K, V> {

		SortedAsMapView(SortedSet<K> set, Function<? super K, V> function) {
			super(set, function);
		}

		@Override
		SortedSet<K> backingSet() {
			return (SortedSet<K>) super.backingSet();
		}

		@Override
		public Comparator<? super K> comparator() {
			return backingSet().comparator();
		}

		@Override
		public Set<K> keySet() {
			return removeOnlySortedSet(backingSet());
		}

		@Override
		public SortedMap<K, V> subMap(K fromKey, K toKey) {
			return asMap(backingSet().subSet(fromKey, toKey), function);
		}

		@Override
		public SortedMap<K, V> headMap(K toKey) {
			return asMap(backingSet().headSet(toKey), function);
		}

		@Override
		public SortedMap<K, V> tailMap(K fromKey) {
			return asMap(backingSet().tailSet(fromKey), function);
		}

		@Override
		public K firstKey() {
			return backingSet().first();
		}

		@Override
		public K lastKey() {
			return backingSet().last();
		}
	}

	@GwtIncompatible("NavigableMap")
	private static final class NavigableAsMapView<K, V> extends AbstractNavigableMap<K, V> {
		/*
		 * Using AbstractNavigableMap is simpler than extending SortedAsMapView and
		 * rewriting all the NavigableMap methods.
		 */

		private final NavigableSet<K> set;
		private final Function<? super K, V> function;

		NavigableAsMapView(NavigableSet<K> ks, Function<? super K, V> vFunction) {
			this.set = checkNotNull(ks);
			this.function = checkNotNull(vFunction);
		}

		@Override
		public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
			return asMap(set.subSet(fromKey, fromInclusive, toKey, toInclusive), function);
		}

		@Override
		public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
			return asMap(set.headSet(toKey, inclusive), function);
		}

		@Override
		public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
			return asMap(set.tailSet(fromKey, inclusive), function);
		}

		@Override
		public Comparator<? super K> comparator() {
			return set.comparator();
		}

		@Override
		@Nullable
		public V get(@Nullable Object key) {
			if (Collections2.safeContains(set, key)) {
				@SuppressWarnings("unchecked") // unsafe, but Javadoc warns about it
				K k = (K) key;
				return function.apply(k);
			} else {
				return null;
			}
		}

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

		@Override
		Iterator<Entry<K, V>> entryIterator() {
			return asMapEntryIterator(set, function);
		}

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

		@Override
		public NavigableSet<K> navigableKeySet() {
			return removeOnlyNavigableSet(set);
		}

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

		@Override
		public NavigableMap<K, V> descendingMap() {
			return asMap(set.descendingSet(), function);
		}
	}

	private static <E> Set<E> removeOnlySet(final Set<E> set) {
		return new ForwardingSet<E>() {
			@Override
			protected Set<E> delegate() {
				return set;
			}

			@Override
			public boolean add(E element) {
				throw new UnsupportedOperationException();
			}

			@Override
			public boolean addAll(Collection<? extends E> es) {
				throw new UnsupportedOperationException();
			}
		};
	}

	private static <E> SortedSet<E> removeOnlySortedSet(final SortedSet<E> set) {
		return new ForwardingSortedSet<E>() {
			@Override
			protected SortedSet<E> delegate() {
				return set;
			}

			@Override
			public boolean add(E element) {
				throw new UnsupportedOperationException();
			}

			@Override
			public boolean addAll(Collection<? extends E> es) {
				throw new UnsupportedOperationException();
			}

			@Override
			public SortedSet<E> headSet(E toElement) {
				return removeOnlySortedSet(super.headSet(toElement));
			}

			@Override
			public SortedSet<E> subSet(E fromElement, E toElement) {
				return removeOnlySortedSet(super.subSet(fromElement, toElement));
			}

			@Override
			public SortedSet<E> tailSet(E fromElement) {
				return removeOnlySortedSet(super.tailSet(fromElement));
			}
		};
	}

	@GwtIncompatible("NavigableSet")
	private static <E> NavigableSet<E> removeOnlyNavigableSet(final NavigableSet<E> set) {
		return new ForwardingNavigableSet<E>() {
			@Override
			protected NavigableSet<E> delegate() {
				return set;
			}

			@Override
			public boolean add(E element) {
				throw new UnsupportedOperationException();
			}

			@Override
			public boolean addAll(Collection<? extends E> es) {
				throw new UnsupportedOperationException();
			}

			@Override
			public SortedSet<E> headSet(E toElement) {
				return removeOnlySortedSet(super.headSet(toElement));
			}

			@Override
			public SortedSet<E> subSet(E fromElement, E toElement) {
				return removeOnlySortedSet(super.subSet(fromElement, toElement));
			}

			@Override
			public SortedSet<E> tailSet(E fromElement) {
				return removeOnlySortedSet(super.tailSet(fromElement));
			}

			@Override
			public NavigableSet<E> headSet(E toElement, boolean inclusive) {
				return removeOnlyNavigableSet(super.headSet(toElement, inclusive));
			}

			@Override
			public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
				return removeOnlyNavigableSet(super.tailSet(fromElement, inclusive));
			}

			@Override
			public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
				return removeOnlyNavigableSet(super.subSet(fromElement, fromInclusive, toElement, toInclusive));
			}

			@Override
			public NavigableSet<E> descendingSet() {
				return removeOnlyNavigableSet(super.descendingSet());
			}
		};
	}

	/**
	 * Returns an immutable map whose keys are the distinct elements of {@code
	 * keys} and whose value for each key was computed by {@code valueFunction}. The
	 * map's iteration order is the order of the first appearance of each key in
	 * {@code keys}.
	 *
	 * <p>
	 * If {@code keys} is a {@link Set}, a live view can be obtained instead of a
	 * copy using {@link Maps#asMap(Set, Function)}.
	 *
	 * @throws NullPointerException if any element of {@code keys} is {@code null},
	 *                              or if {@code valueFunction} produces
	 *                              {@code null} for any key
	 * @since 14.0
	 */
	@Beta
	public static <K, V> ImmutableMap<K, V> toMap(Iterable<K> keys, Function<? super K, V> valueFunction) {
		return toMap(keys.iterator(), valueFunction);
	}

	/**
	 * Returns an immutable map whose keys are the distinct elements of {@code
	 * keys} and whose value for each key was computed by {@code valueFunction}. The
	 * map's iteration order is the order of the first appearance of each key in
	 * {@code keys}.
	 *
	 * @throws NullPointerException if any element of {@code keys} is {@code null},
	 *                              or if {@code valueFunction} produces
	 *                              {@code null} for any key
	 * @since 14.0
	 */
	@Beta
	public static <K, V> ImmutableMap<K, V> toMap(Iterator<K> keys, Function<? super K, V> valueFunction) {
		checkNotNull(valueFunction);
		// Using LHM instead of a builder so as not to fail on duplicate keys
		Map<K, V> builder = newLinkedHashMap();
		while (keys.hasNext()) {
			K key = keys.next();
			builder.put(key, valueFunction.apply(key));
		}
		return ImmutableMap.copyOf(builder);
	}

	/**
	 * Returns an immutable map for which the {@link Map#values} are the given
	 * elements in the given order, and each key is the product of invoking a
	 * supplied function on its corresponding value.
	 *
	 * @param values      the values to use when constructing the {@code Map}
	 * @param keyFunction the function used to produce the key for each value
	 * @return a map mapping the result of evaluating the function {@code
	 *         keyFunction} on each value in the input collection to that value
	 * @throws IllegalArgumentException if {@code keyFunction} produces the same key
	 *                                  for more than one value in the input
	 *                                  collection
	 * @throws NullPointerException     if any elements of {@code values} is null,
	 *                                  or if {@code keyFunction} produces
	 *                                  {@code null} for any value
	 */
	public static <K, V> ImmutableMap<K, V> uniqueIndex(Iterable<V> values, Function<? super V, K> keyFunction) {
		return uniqueIndex(values.iterator(), keyFunction);
	}

	/**
	 * Returns an immutable map for which the {@link Map#values} are the given
	 * elements in the given order, and each key is the product of invoking a
	 * supplied function on its corresponding value.
	 *
	 * @param values      the values to use when constructing the {@code Map}
	 * @param keyFunction the function used to produce the key for each value
	 * @return a map mapping the result of evaluating the function {@code
	 *         keyFunction} on each value in the input collection to that value
	 * @throws IllegalArgumentException if {@code keyFunction} produces the same key
	 *                                  for more than one value in the input
	 *                                  collection
	 * @throws NullPointerException     if any elements of {@code values} is null,
	 *                                  or if {@code keyFunction} produces
	 *                                  {@code null} for any value
	 * @since 10.0
	 */
	public static <K, V> ImmutableMap<K, V> uniqueIndex(Iterator<V> values, Function<? super V, K> keyFunction) {
		checkNotNull(keyFunction);
		ImmutableMap.Builder<K, V> builder = ImmutableMap.builder();
		while (values.hasNext()) {
			V value = values.next();
			builder.put(keyFunction.apply(value), value);
		}
		return builder.build();
	}

	/**
	 * Creates an {@code ImmutableMap<String, String>} from a {@code Properties}
	 * instance. Properties normally derive from {@code Map<Object, Object>}, but
	 * they typically contain strings, which is awkward. This method lets you get a
	 * plain-old-{@code Map} out of a {@code Properties}.
	 *
	 * @param properties a {@code Properties} object to be converted
	 * @return an immutable map containing all the entries in {@code properties}
	 * @throws ClassCastException   if any key in {@code Properties} is not a {@code
	 *         String}
	 * @throws NullPointerException if any key or value in {@code Properties} is
	 *                              null
	 */
	@GwtIncompatible("java.util.Properties")
	public static ImmutableMap<String, String> fromProperties(Properties properties) {
		ImmutableMap.Builder<String, String> builder = ImmutableMap.builder();

		for (Enumeration<?> e = properties.propertyNames(); e.hasMoreElements();) {
			String key = (String) e.nextElement();
			builder.put(key, properties.getProperty(key));
		}

		return builder.build();
	}

	/**
	 * Returns an immutable map entry with the specified key and value. The
	 * {@link Entry#setValue} operation throws an
	 * {@link UnsupportedOperationException}.
	 *
	 * <p>
	 * The returned entry is serializable.
	 *
	 * @param key   the key to be associated with the returned entry
	 * @param value the value to be associated with the returned entry
	 */
	@GwtCompatible(serializable = true)
	public static <K, V> Entry<K, V> immutableEntry(@Nullable K key, @Nullable V value) {
		return new ImmutableEntry<K, V>(key, value);
	}

	/**
	 * Returns an unmodifiable view of the specified set of entries. The
	 * {@link Entry#setValue} operation throws an
	 * {@link UnsupportedOperationException}, as do any operations that would modify
	 * the returned set.
	 *
	 * @param entrySet the entries for which to return an unmodifiable view
	 * @return an unmodifiable view of the entries
	 */
	static <K, V> Set<Entry<K, V>> unmodifiableEntrySet(Set<Entry<K, V>> entrySet) {
		return new UnmodifiableEntrySet<K, V>(Collections.unmodifiableSet(entrySet));
	}

	/**
	 * Returns an unmodifiable view of the specified map entry. The
	 * {@link Entry#setValue} operation throws an
	 * {@link UnsupportedOperationException}. This also has the side-effect of
	 * redefining {@code equals} to comply with the Entry contract, to avoid a
	 * possible nefarious implementation of equals.
	 *
	 * @param entry the entry for which to return an unmodifiable view
	 * @return an unmodifiable view of the entry
	 */
	static <K, V> Entry<K, V> unmodifiableEntry(final Entry<? extends K, ? extends V> entry) {
		checkNotNull(entry);
		return new AbstractMapEntry<K, V>() {
			@Override
			public K getKey() {
				return entry.getKey();
			}

			@Override
			public V getValue() {
				return entry.getValue();
			}
		};
	}

	/** @see Multimaps#unmodifiableEntries */
	static class UnmodifiableEntries<K, V> extends ForwardingCollection<Entry<K, V>> {
		private final Collection<Entry<K, V>> entries;

		UnmodifiableEntries(Collection<Entry<K, V>> entries) {
			this.entries = entries;
		}

		@Override
		protected Collection<Entry<K, V>> delegate() {
			return entries;
		}

		@Override
		public Iterator<Entry<K, V>> iterator() {
			final Iterator<Entry<K, V>> delegate = super.iterator();
			return new UnmodifiableIterator<Entry<K, V>>() {
				@Override
				public boolean hasNext() {
					return delegate.hasNext();
				}

				@Override
				public Entry<K, V> next() {
					return unmodifiableEntry(delegate.next());
				}
			};
		}

		// See java.util.Collections.UnmodifiableEntrySet for details on attacks.

		@Override
		public Object[] toArray() {
			return standardToArray();
		}

		@Override
		public <T> T[] toArray(T[] array) {
			return standardToArray(array);
		}
	}

	/** @see Maps#unmodifiableEntrySet(Set) */
	static class UnmodifiableEntrySet<K, V> extends UnmodifiableEntries<K, V> implements Set<Entry<K, V>> {
		UnmodifiableEntrySet(Set<Entry<K, V>> entries) {
			super(entries);
		}

		// See java.util.Collections.UnmodifiableEntrySet for details on attacks.

		@Override
		public boolean equals(@Nullable Object object) {
			return Sets.equalsImpl(this, object);
		}

		@Override
		public int hashCode() {
			return Sets.hashCodeImpl(this);
		}
	}

	/**
	 * Returns a {@link Converter} that converts values using {@link BiMap#get
	 * bimap.get()}, and whose inverse view converts values using
	 * {@link BiMap#inverse bimap.inverse()}{@code .get()}.
	 *
	 * <p>
	 * To use a plain {@link Map} as a {@link Function}, see
	 * {@link com.google.common.base.Functions#forMap(Map)} or
	 * {@link com.google.common.base.Functions#forMap(Map, Object)}.
	 *
	 * @since 16.0
	 */
	@Beta
	public static <A, B> Converter<A, B> asConverter(final BiMap<A, B> bimap) {
		return new BiMapConverter<A, B>(bimap);
	}

	private static final class BiMapConverter<A, B> extends Converter<A, B> implements Serializable {
		private final BiMap<A, B> bimap;

		BiMapConverter(BiMap<A, B> bimap) {
			this.bimap = checkNotNull(bimap);
		}

		@Override
		protected B doForward(A a) {
			return convert(bimap, a);
		}

		@Override
		protected A doBackward(B b) {
			return convert(bimap.inverse(), b);
		}

		private static <X, Y> Y convert(BiMap<X, Y> bimap, X input) {
			Y output = bimap.get(input);
			checkArgument(output != null, "No non-null mapping present for input: %s", input);
			return output;
		}

		@Override
		public boolean equals(@Nullable Object object) {
			if (object instanceof BiMapConverter) {
				BiMapConverter<?, ?> that = (BiMapConverter<?, ?>) object;
				return this.bimap.equals(that.bimap);
			}
			return false;
		}

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

		// There's really no good way to implement toString() without printing the
		// entire BiMap, right?
		@Override
		public String toString() {
			return "Maps.asConverter(" + bimap + ")";
		}

		private static final long serialVersionUID = 0L;
	}

	/**
	 * Returns a synchronized (thread-safe) bimap backed by the specified bimap. In
	 * order to guarantee serial access, it is critical that <b>all</b> access to
	 * the backing bimap is accomplished through the returned bimap.
	 *
	 * <p>
	 * It is imperative that the user manually synchronize on the returned map when
	 * accessing any of its collection views:
	 * 
	 * <pre>
	 *    {@code
	 *
	 *   BiMap<Long, String> map = Maps.synchronizedBiMap(
	 *       HashBiMap.<Long, String>create());
	 *   ...
	 *   Set<Long> set = map.keySet();  // Needn't be in synchronized block
	 *   ...
	 *   synchronized (map) {  // Synchronizing on map, not set!
	 *     Iterator<Long> it = set.iterator(); // Must be in synchronized block
	 *     while (it.hasNext()) {
	 *       foo(it.next());
	 *     }
	 *   }}
	 * </pre>
	 *
	 * <p>
	 * Failure to follow this advice may result in non-deterministic behavior.
	 *
	 * <p>
	 * The returned bimap will be serializable if the specified bimap is
	 * serializable.
	 *
	 * @param bimap the bimap to be wrapped in a synchronized view
	 * @return a sychronized view of the specified bimap
	 */
	public static <K, V> BiMap<K, V> synchronizedBiMap(BiMap<K, V> bimap) {
		return Synchronized.biMap(bimap, null);
	}

	/**
	 * Returns an unmodifiable view of the specified bimap. This method allows
	 * modules to provide users with "read-only" access to internal bimaps. Query
	 * operations on the returned bimap "read through" to the specified bimap, and
	 * attempts to modify the returned map, whether direct or via its collection
	 * views, result in an {@code UnsupportedOperationException}.
	 *
	 * <p>
	 * The returned bimap will be serializable if the specified bimap is
	 * serializable.
	 *
	 * @param bimap the bimap for which an unmodifiable view is to be returned
	 * @return an unmodifiable view of the specified bimap
	 */
	public static <K, V> BiMap<K, V> unmodifiableBiMap(BiMap<? extends K, ? extends V> bimap) {
		return new UnmodifiableBiMap<K, V>(bimap, null);
	}

	/** @see Maps#unmodifiableBiMap(BiMap) */
	private static class UnmodifiableBiMap<K, V> extends ForwardingMap<K, V> implements BiMap<K, V>, Serializable {
		final Map<K, V> unmodifiableMap;
		final BiMap<? extends K, ? extends V> delegate;
		BiMap<V, K> inverse;
		transient Set<V> values;

		UnmodifiableBiMap(BiMap<? extends K, ? extends V> delegate, @Nullable BiMap<V, K> inverse) {
			unmodifiableMap = Collections.unmodifiableMap(delegate);
			this.delegate = delegate;
			this.inverse = inverse;
		}

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

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

		@Override
		public BiMap<V, K> inverse() {
			BiMap<V, K> result = inverse;
			return (result == null) ? inverse = new UnmodifiableBiMap<V, K>(delegate.inverse(), this) : result;
		}

		@Override
		public Set<V> values() {
			Set<V> result = values;
			return (result == null) ? values = Collections.unmodifiableSet(delegate.values()) : result;
		}

		private static final long serialVersionUID = 0;
	}

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

	/**
	 * Returns a view of a sorted map where each value is transformed by a function.
	 * All other properties of the map, such as iteration order, are left intact.
	 * For example, the code:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	SortedMap<String, Integer> map = ImmutableSortedMap.of("a", 4, "b", 9);
	 * 	Function<Integer, Double> sqrt = new Function<Integer, Double>() {
	 * 		public Double apply(Integer in) {
	 * 			return Math.sqrt((int) in);
	 * 		}
	 * 	};
	 * 	SortedMap<String, Double> transformed = Maps.transformValues(map, sqrt);
	 * 	System.out.println(transformed);
	 * }
	 * </pre>
	 *
	 * ... prints {@code {a=2.0, b=3.0}}.
	 *
	 * <p>
	 * Changes in the underlying map are reflected in this view. Conversely, this
	 * view supports removal operations, and these are reflected in the underlying
	 * map.
	 *
	 * <p>
	 * It's acceptable for the underlying map to contain null keys, and even null
	 * values provided that the function is capable of accepting null input. The
	 * transformed map might contain null values, if the function sometimes gives a
	 * null result.
	 *
	 * <p>
	 * The returned map is not thread-safe or serializable, even if the underlying
	 * map is.
	 *
	 * <p>
	 * The function is applied lazily, invoked when needed. This is necessary for
	 * the returned map to be a view, but it means that the function will be applied
	 * many times for bulk operations like {@link Map#containsValue} and
	 * {@code Map.toString()}. For this to perform well, {@code function} should be
	 * fast. To avoid lazy evaluation when the returned map doesn't need to be a
	 * view, copy the returned map into a new map of your choosing.
	 *
	 * @since 11.0
	 */
	public static <K, V1, V2> SortedMap<K, V2> transformValues(SortedMap<K, V1> fromMap,
			Function<? super V1, V2> function) {
		return transformEntries(fromMap, asEntryTransformer(function));
	}

	/**
	 * Returns a view of a navigable map where each value is transformed by a
	 * function. All other properties of the map, such as iteration order, are left
	 * intact. For example, the code:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	NavigableMap<String, Integer> map = Maps.newTreeMap();
	 * 	map.put("a", 4);
	 * 	map.put("b", 9);
	 * 	Function<Integer, Double> sqrt = new Function<Integer, Double>() {
	 * 		public Double apply(Integer in) {
	 * 			return Math.sqrt((int) in);
	 * 		}
	 * 	};
	 * 	NavigableMap<String, Double> transformed = Maps.transformNavigableValues(map, sqrt);
	 * 	System.out.println(transformed);
	 * }
	 * </pre>
	 *
	 * ... prints {@code {a=2.0, b=3.0}}.
	 *
	 * Changes in the underlying map are reflected in this view. Conversely, this
	 * view supports removal operations, and these are reflected in the underlying
	 * map.
	 *
	 * <p>
	 * It's acceptable for the underlying map to contain null keys, and even null
	 * values provided that the function is capable of accepting null input. The
	 * transformed map might contain null values, if the function sometimes gives a
	 * null result.
	 *
	 * <p>
	 * The returned map is not thread-safe or serializable, even if the underlying
	 * map is.
	 *
	 * <p>
	 * The function is applied lazily, invoked when needed. This is necessary for
	 * the returned map to be a view, but it means that the function will be applied
	 * many times for bulk operations like {@link Map#containsValue} and
	 * {@code Map.toString()}. For this to perform well, {@code function} should be
	 * fast. To avoid lazy evaluation when the returned map doesn't need to be a
	 * view, copy the returned map into a new map of your choosing.
	 *
	 * @since 13.0
	 */
	@GwtIncompatible("NavigableMap")
	public static <K, V1, V2> NavigableMap<K, V2> transformValues(NavigableMap<K, V1> fromMap,
			Function<? super V1, V2> function) {
		return transformEntries(fromMap, asEntryTransformer(function));
	}

	/**
	 * Returns a view of a map whose values are derived from the original map'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 map, such as iteration order, are
	 * left intact. For example, the code:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	Map<String, Boolean> options = ImmutableMap.of("verbose", true, "sort", false);
	 * 	EntryTransformer<String, Boolean, String> flagPrefixer = new EntryTransformer<String, Boolean, String>() {
	 * 		public String transformEntry(String key, Boolean value) {
	 * 			return value ? key : "no" + key;
	 * 		}
	 * 	};
	 * 	Map<String, String> transformed = Maps.transformEntries(options, flagPrefixer);
	 * 	System.out.println(transformed);
	 * }
	 * </pre>
	 *
	 * ... prints {@code {verbose=verbose, sort=nosort}}.
	 *
	 * <p>
	 * Changes in the underlying map are reflected in this view. Conversely, this
	 * view supports removal operations, and these are reflected in the underlying
	 * map.
	 *
	 * <p>
	 * It's acceptable for the underlying map to contain null keys and null values
	 * provided that the transformer is capable of accepting null inputs. The
	 * transformed map might contain null values if the transformer sometimes gives
	 * a null result.
	 *
	 * <p>
	 * The returned map is not thread-safe or serializable, even if the underlying
	 * map is.
	 *
	 * <p>
	 * The transformer is applied lazily, invoked when needed. This is necessary for
	 * the returned map to be a view, but it means that the transformer will be
	 * applied many times for bulk operations like {@link Map#containsValue} and
	 * {@link Object#toString}. For this to perform well, {@code transformer} should
	 * be fast. To avoid lazy evaluation when the returned map doesn't need to be a
	 * view, copy the returned map into a new map 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 map.
	 *
	 * @since 7.0
	 */
	public static <K, V1, V2> Map<K, V2> transformEntries(Map<K, V1> fromMap,
			EntryTransformer<? super K, ? super V1, V2> transformer) {
		if (fromMap instanceof SortedMap) {
			return transformEntries((SortedMap<K, V1>) fromMap, transformer);
		}
		return new TransformedEntriesMap<K, V1, V2>(fromMap, transformer);
	}

	/**
	 * Returns a view of a sorted map whose values are derived from the original
	 * sorted map'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 map, such as iteration order, are
	 * left intact. For example, the code:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	Map<String, Boolean> options = ImmutableSortedMap.of("verbose", true, "sort", false);
	 * 	EntryTransformer<String, Boolean, String> flagPrefixer = new EntryTransformer<String, Boolean, String>() {
	 * 		public String transformEntry(String key, Boolean value) {
	 * 			return value ? key : "yes" + key;
	 * 		}
	 * 	};
	 * 	SortedMap<String, String> transformed = Maps.transformEntries(options, flagPrefixer);
	 * 	System.out.println(transformed);
	 * }
	 * </pre>
	 *
	 * ... prints {@code {sort=yessort, verbose=verbose}}.
	 *
	 * <p>
	 * Changes in the underlying map are reflected in this view. Conversely, this
	 * view supports removal operations, and these are reflected in the underlying
	 * map.
	 *
	 * <p>
	 * It's acceptable for the underlying map to contain null keys and null values
	 * provided that the transformer is capable of accepting null inputs. The
	 * transformed map might contain null values if the transformer sometimes gives
	 * a null result.
	 *
	 * <p>
	 * The returned map is not thread-safe or serializable, even if the underlying
	 * map is.
	 *
	 * <p>
	 * The transformer is applied lazily, invoked when needed. This is necessary for
	 * the returned map to be a view, but it means that the transformer will be
	 * applied many times for bulk operations like {@link Map#containsValue} and
	 * {@link Object#toString}. For this to perform well, {@code transformer} should
	 * be fast. To avoid lazy evaluation when the returned map doesn't need to be a
	 * view, copy the returned map into a new map 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 map.
	 *
	 * @since 11.0
	 */
	public static <K, V1, V2> SortedMap<K, V2> transformEntries(SortedMap<K, V1> fromMap,
			EntryTransformer<? super K, ? super V1, V2> transformer) {
		return Platform.mapsTransformEntriesSortedMap(fromMap, transformer);
	}

	/**
	 * Returns a view of a navigable map whose values are derived from the original
	 * navigable map'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 map, such as iteration order, are
	 * left intact. For example, the code:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	NavigableMap<String, Boolean> options = Maps.newTreeMap();
	 * 	options.put("verbose", false);
	 * 	options.put("sort", true);
	 * 	EntryTransformer<String, Boolean, String> flagPrefixer = new EntryTransformer<String, Boolean, String>() {
	 * 		public String transformEntry(String key, Boolean value) {
	 * 			return value ? key : ("yes" + key);
	 * 		}
	 * 	};
	 * 	NavigableMap<String, String> transformed = LabsMaps.transformNavigableEntries(options, flagPrefixer);
	 * 	System.out.println(transformed);
	 * }
	 * </pre>
	 *
	 * ... prints {@code {sort=yessort, verbose=verbose}}.
	 *
	 * <p>
	 * Changes in the underlying map are reflected in this view. Conversely, this
	 * view supports removal operations, and these are reflected in the underlying
	 * map.
	 *
	 * <p>
	 * It's acceptable for the underlying map to contain null keys and null values
	 * provided that the transformer is capable of accepting null inputs. The
	 * transformed map might contain null values if the transformer sometimes gives
	 * a null result.
	 *
	 * <p>
	 * The returned map is not thread-safe or serializable, even if the underlying
	 * map is.
	 *
	 * <p>
	 * The transformer is applied lazily, invoked when needed. This is necessary for
	 * the returned map to be a view, but it means that the transformer will be
	 * applied many times for bulk operations like {@link Map#containsValue} and
	 * {@link Object#toString}. For this to perform well, {@code transformer} should
	 * be fast. To avoid lazy evaluation when the returned map doesn't need to be a
	 * view, copy the returned map into a new map 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 map.
	 *
	 * @since 13.0
	 */
	@GwtIncompatible("NavigableMap")
	public static <K, V1, V2> NavigableMap<K, V2> transformEntries(final NavigableMap<K, V1> fromMap,
			EntryTransformer<? super K, ? super V1, V2> transformer) {
		return new TransformedEntriesNavigableMap<K, V1, V2>(fromMap, transformer);
	}

	static <K, V1, V2> SortedMap<K, V2> transformEntriesIgnoreNavigable(SortedMap<K, V1> fromMap,
			EntryTransformer<? super K, ? super V1, V2> transformer) {
		return new TransformedEntriesSortedMap<K, V1, V2>(fromMap, transformer);
	}

	/**
	 * A transformation of the value of a key-value pair, using both key and value
	 * as inputs. To apply the transformation to a map, use
	 * {@link Maps#transformEntries(Map, EntryTransformer)}.
	 *
	 * @param <K>  the key type of the input and output entries
	 * @param <V1> the value type of the input entry
	 * @param <V2> the value type of the output entry
	 * @since 7.0
	 */
	public interface EntryTransformer<K, V1, V2> {
		/**
		 * Determines an output value based on a key-value pair. This method is
		 * <i>generally expected</i>, but not absolutely required, to have the following
		 * properties:
		 *
		 * <ul>
		 * <li>Its execution does not cause any observable side effects.
		 * <li>The computation is <i>consistent with equals</i>; that is,
		 * {@link Objects#equal Objects.equal}{@code (k1, k2) &&}
		 * {@link Objects#equal}{@code (v1, v2)} implies that {@code
		 *     Objects.equal(transformer.transform(k1, v1),
		 *     transformer.transform(k2, v2))}.
		 * </ul>
		 *
		 * @throws NullPointerException if the key or value is null and this transformer
		 *                              does not accept null arguments
		 */
		V2 transformEntry(@Nullable K key, @Nullable V1 value);
	}

	/**
	 * Views a function as an entry transformer that ignores the entry key.
	 */
	static <K, V1, V2> EntryTransformer<K, V1, V2> asEntryTransformer(final Function<? super V1, V2> function) {
		checkNotNull(function);
		return new EntryTransformer<K, V1, V2>() {
			@Override
			public V2 transformEntry(K key, V1 value) {
				return function.apply(value);
			}
		};
	}

	static <K, V1, V2> Function<V1, V2> asValueToValueFunction(final EntryTransformer<? super K, V1, V2> transformer,
			final K key) {
		checkNotNull(transformer);
		return new Function<V1, V2>() {
			@Override
			public V2 apply(@Nullable V1 v1) {
				return transformer.transformEntry(key, v1);
			}
		};
	}

	/**
	 * Views an entry transformer as a function from {@code Entry} to values.
	 */
	static <K, V1, V2> Function<Entry<K, V1>, V2> asEntryToValueFunction(
			final EntryTransformer<? super K, ? super V1, V2> transformer) {
		checkNotNull(transformer);
		return new Function<Entry<K, V1>, V2>() {
			@Override
			public V2 apply(Entry<K, V1> entry) {
				return transformer.transformEntry(entry.getKey(), entry.getValue());
			}
		};
	}

	/**
	 * Returns a view of an entry transformed by the specified transformer.
	 */
	static <V2, K, V1> Entry<K, V2> transformEntry(final EntryTransformer<? super K, ? super V1, V2> transformer,
			final Entry<K, V1> entry) {
		checkNotNull(transformer);
		checkNotNull(entry);
		return new AbstractMapEntry<K, V2>() {
			@Override
			public K getKey() {
				return entry.getKey();
			}

			@Override
			public V2 getValue() {
				return transformer.transformEntry(entry.getKey(), entry.getValue());
			}
		};
	}

	/**
	 * Views an entry transformer as a function from entries to entries.
	 */
	static <K, V1, V2> Function<Entry<K, V1>, Entry<K, V2>> asEntryToEntryFunction(
			final EntryTransformer<? super K, ? super V1, V2> transformer) {
		checkNotNull(transformer);
		return new Function<Entry<K, V1>, Entry<K, V2>>() {
			@Override
			public Entry<K, V2> apply(final Entry<K, V1> entry) {
				return transformEntry(transformer, entry);
			}
		};
	}

	static class TransformedEntriesMap<K, V1, V2> extends ImprovedAbstractMap<K, V2> {
		final Map<K, V1> fromMap;
		final EntryTransformer<? super K, ? super V1, V2> transformer;

		TransformedEntriesMap(Map<K, V1> fromMap, EntryTransformer<? super K, ? super V1, V2> transformer) {
			this.fromMap = checkNotNull(fromMap);
			this.transformer = checkNotNull(transformer);
		}

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

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

		// safe as long as the user followed the <b>Warning</b> in the javadoc
		@SuppressWarnings("unchecked")
		@Override
		public V2 get(Object key) {
			V1 value = fromMap.get(key);
			return (value != null || fromMap.containsKey(key)) ? transformer.transformEntry((K) key, value) : null;
		}

		// safe as long as the user followed the <b>Warning</b> in the javadoc
		@SuppressWarnings("unchecked")
		@Override
		public V2 remove(Object key) {
			return fromMap.containsKey(key) ? transformer.transformEntry((K) key, fromMap.remove(key)) : null;
		}

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

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

		@Override
		protected Set<Entry<K, V2>> createEntrySet() {
			return new EntrySet<K, V2>() {
				@Override
				Map<K, V2> map() {
					return TransformedEntriesMap.this;
				}

				@Override
				public Iterator<Entry<K, V2>> iterator() {
					return Iterators.transform(fromMap.entrySet().iterator(),
							Maps.<K, V1, V2>asEntryToEntryFunction(transformer));
				}
			};
		}
	}

	static class TransformedEntriesSortedMap<K, V1, V2> extends TransformedEntriesMap<K, V1, V2>
			implements SortedMap<K, V2> {

		protected SortedMap<K, V1> fromMap() {
			return (SortedMap<K, V1>) fromMap;
		}

		TransformedEntriesSortedMap(SortedMap<K, V1> fromMap, EntryTransformer<? super K, ? super V1, V2> transformer) {
			super(fromMap, transformer);
		}

		@Override
		public Comparator<? super K> comparator() {
			return fromMap().comparator();
		}

		@Override
		public K firstKey() {
			return fromMap().firstKey();
		}

		@Override
		public SortedMap<K, V2> headMap(K toKey) {
			return transformEntries(fromMap().headMap(toKey), transformer);
		}

		@Override
		public K lastKey() {
			return fromMap().lastKey();
		}

		@Override
		public SortedMap<K, V2> subMap(K fromKey, K toKey) {
			return transformEntries(fromMap().subMap(fromKey, toKey), transformer);
		}

		@Override
		public SortedMap<K, V2> tailMap(K fromKey) {
			return transformEntries(fromMap().tailMap(fromKey), transformer);
		}
	}

	@GwtIncompatible("NavigableMap")
	private static class TransformedEntriesNavigableMap<K, V1, V2> extends TransformedEntriesSortedMap<K, V1, V2>
			implements NavigableMap<K, V2> {

		TransformedEntriesNavigableMap(NavigableMap<K, V1> fromMap,
				EntryTransformer<? super K, ? super V1, V2> transformer) {
			super(fromMap, transformer);
		}

		@Override
		public Entry<K, V2> ceilingEntry(K key) {
			return transformEntry(fromMap().ceilingEntry(key));
		}

		@Override
		public K ceilingKey(K key) {
			return fromMap().ceilingKey(key);
		}

		@Override
		public NavigableSet<K> descendingKeySet() {
			return fromMap().descendingKeySet();
		}

		@Override
		public NavigableMap<K, V2> descendingMap() {
			return transformEntries(fromMap().descendingMap(), transformer);
		}

		@Override
		public Entry<K, V2> firstEntry() {
			return transformEntry(fromMap().firstEntry());
		}

		@Override
		public Entry<K, V2> floorEntry(K key) {
			return transformEntry(fromMap().floorEntry(key));
		}

		@Override
		public K floorKey(K key) {
			return fromMap().floorKey(key);
		}

		@Override
		public NavigableMap<K, V2> headMap(K toKey) {
			return headMap(toKey, false);
		}

		@Override
		public NavigableMap<K, V2> headMap(K toKey, boolean inclusive) {
			return transformEntries(fromMap().headMap(toKey, inclusive), transformer);
		}

		@Override
		public Entry<K, V2> higherEntry(K key) {
			return transformEntry(fromMap().higherEntry(key));
		}

		@Override
		public K higherKey(K key) {
			return fromMap().higherKey(key);
		}

		@Override
		public Entry<K, V2> lastEntry() {
			return transformEntry(fromMap().lastEntry());
		}

		@Override
		public Entry<K, V2> lowerEntry(K key) {
			return transformEntry(fromMap().lowerEntry(key));
		}

		@Override
		public K lowerKey(K key) {
			return fromMap().lowerKey(key);
		}

		@Override
		public NavigableSet<K> navigableKeySet() {
			return fromMap().navigableKeySet();
		}

		@Override
		public Entry<K, V2> pollFirstEntry() {
			return transformEntry(fromMap().pollFirstEntry());
		}

		@Override
		public Entry<K, V2> pollLastEntry() {
			return transformEntry(fromMap().pollLastEntry());
		}

		@Override
		public NavigableMap<K, V2> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
			return transformEntries(fromMap().subMap(fromKey, fromInclusive, toKey, toInclusive), transformer);
		}

		@Override
		public NavigableMap<K, V2> subMap(K fromKey, K toKey) {
			return subMap(fromKey, true, toKey, false);
		}

		@Override
		public NavigableMap<K, V2> tailMap(K fromKey) {
			return tailMap(fromKey, true);
		}

		@Override
		public NavigableMap<K, V2> tailMap(K fromKey, boolean inclusive) {
			return transformEntries(fromMap().tailMap(fromKey, inclusive), transformer);
		}

		@Nullable
		private Entry<K, V2> transformEntry(@Nullable Entry<K, V1> entry) {
			return (entry == null) ? null : Maps.transformEntry(transformer, entry);
		}

		@Override
		protected NavigableMap<K, V1> fromMap() {
			return (NavigableMap<K, V1>) super.fromMap();
		}
	}

	static <K> Predicate<Entry<K, ?>> keyPredicateOnEntries(Predicate<? super K> keyPredicate) {
		return compose(keyPredicate, Maps.<K>keyFunction());
	}

	static <V> Predicate<Entry<?, V>> valuePredicateOnEntries(Predicate<? super V> valuePredicate) {
		return compose(valuePredicate, Maps.<V>valueFunction());
	}

	/**
	 * Returns a map containing the mappings in {@code unfiltered} whose keys
	 * satisfy a predicate. The returned map is a live view of {@code unfiltered};
	 * changes to one affect the other.
	 *
	 * <p>
	 * The resulting map's {@code keySet()}, {@code entrySet()}, and {@code
	 * values()} views have iterators that don't support {@code remove()}, but all
	 * other methods are supported by the map and its views. When given a key that
	 * doesn't satisfy the predicate, the map's {@code put()} and {@code putAll()}
	 * methods throw an {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered map or its views, only mappings whose keys satisfy the filter
	 * will be removed from the underlying map.
	 *
	 * <p>
	 * The returned map isn't threadsafe or serializable, even if {@code
	 * unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered map's methods, such as {@code size()}, iterate across
	 * every key/value mapping in the underlying map and determine which satisfy the
	 * filter. When a live view is <i>not</i> needed, it may be faster to copy the
	 * filtered map 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.
	 */
	public static <K, V> Map<K, V> filterKeys(Map<K, V> unfiltered, final Predicate<? super K> keyPredicate) {
		if (unfiltered instanceof SortedMap) {
			return filterKeys((SortedMap<K, V>) unfiltered, keyPredicate);
		} else if (unfiltered instanceof BiMap) {
			return filterKeys((BiMap<K, V>) unfiltered, keyPredicate);
		}
		checkNotNull(keyPredicate);
		Predicate<Entry<K, ?>> entryPredicate = keyPredicateOnEntries(keyPredicate);
		return (unfiltered instanceof AbstractFilteredMap)
				? filterFiltered((AbstractFilteredMap<K, V>) unfiltered, entryPredicate)
				: new FilteredKeyMap<K, V>(checkNotNull(unfiltered), keyPredicate, entryPredicate);
	}

	/**
	 * Returns a sorted map containing the mappings in {@code unfiltered} whose keys
	 * satisfy a predicate. The returned map is a live view of {@code
	 * unfiltered}; changes to one affect the other.
	 *
	 * <p>
	 * The resulting map's {@code keySet()}, {@code entrySet()}, and {@code
	 * values()} views have iterators that don't support {@code remove()}, but all
	 * other methods are supported by the map and its views. When given a key that
	 * doesn't satisfy the predicate, the map's {@code put()} and {@code putAll()}
	 * methods throw an {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered map or its views, only mappings whose keys satisfy the filter
	 * will be removed from the underlying map.
	 *
	 * <p>
	 * The returned map isn't threadsafe or serializable, even if {@code
	 * unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered map's methods, such as {@code size()}, iterate across
	 * every key/value mapping in the underlying map and determine which satisfy the
	 * filter. When a live view is <i>not</i> needed, it may be faster to copy the
	 * filtered map 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> SortedMap<K, V> filterKeys(SortedMap<K, V> unfiltered,
			final Predicate<? super K> keyPredicate) {
		// TODO(user): Return a subclass of Maps.FilteredKeyMap for slightly better
		// performance.
		return filterEntries(unfiltered, Maps.<K>keyPredicateOnEntries(keyPredicate));
	}

	/**
	 * Returns a navigable map containing the mappings in {@code unfiltered} whose
	 * keys satisfy a predicate. The returned map is a live view of {@code
	 * unfiltered}; changes to one affect the other.
	 *
	 * <p>
	 * The resulting map's {@code keySet()}, {@code entrySet()}, and {@code
	 * values()} views have iterators that don't support {@code remove()}, but all
	 * other methods are supported by the map and its views. When given a key that
	 * doesn't satisfy the predicate, the map's {@code put()} and {@code putAll()}
	 * methods throw an {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered map or its views, only mappings whose keys satisfy the filter
	 * will be removed from the underlying map.
	 *
	 * <p>
	 * The returned map isn't threadsafe or serializable, even if {@code
	 * unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered map's methods, such as {@code size()}, iterate across
	 * every key/value mapping in the underlying map and determine which satisfy the
	 * filter. When a live view is <i>not</i> needed, it may be faster to copy the
	 * filtered map 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
	 */
	@GwtIncompatible("NavigableMap")
	public static <K, V> NavigableMap<K, V> filterKeys(NavigableMap<K, V> unfiltered,
			final Predicate<? super K> keyPredicate) {
		// TODO(user): Return a subclass of Maps.FilteredKeyMap for slightly better
		// performance.
		return filterEntries(unfiltered, Maps.<K>keyPredicateOnEntries(keyPredicate));
	}

	/**
	 * Returns a bimap containing the mappings in {@code unfiltered} whose keys
	 * satisfy a predicate. The returned bimap is a live view of {@code unfiltered};
	 * changes to one affect the other.
	 *
	 * <p>
	 * The resulting bimap's {@code keySet()}, {@code entrySet()}, and
	 * {@code values()} views have iterators that don't support {@code remove()},
	 * but all other methods are supported by the bimap and its views. When given a
	 * key that doesn't satisfy the predicate, the bimap's {@code
	 * put()}, {@code forcePut()} and {@code putAll()} methods throw an
	 * {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered bimap or its views, only mappings that satisfy the filter will
	 * be removed from the underlying bimap.
	 *
	 * <p>
	 * The returned bimap isn't threadsafe or serializable, even if
	 * {@code unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered bimap's methods, such as {@code size()}, iterate across
	 * every key in the underlying bimap and determine which satisfy the filter.
	 * When a live view is <i>not</i> needed, it may be faster to copy the filtered
	 * bimap 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> BiMap<K, V> filterKeys(BiMap<K, V> unfiltered, final Predicate<? super K> keyPredicate) {
		checkNotNull(keyPredicate);
		return filterEntries(unfiltered, Maps.<K>keyPredicateOnEntries(keyPredicate));
	}

	/**
	 * Returns a map containing the mappings in {@code unfiltered} whose values
	 * satisfy a predicate. The returned map is a live view of {@code unfiltered};
	 * changes to one affect the other.
	 *
	 * <p>
	 * The resulting map's {@code keySet()}, {@code entrySet()}, and {@code
	 * values()} views have iterators that don't support {@code remove()}, but all
	 * other methods are supported by the map and its views. When given a value that
	 * doesn't satisfy the predicate, the map's {@code put()}, {@code
	 * putAll()}, and {@link Entry#setValue} methods throw an
	 * {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered map or its views, only mappings whose values satisfy the filter
	 * will be removed from the underlying map.
	 *
	 * <p>
	 * The returned map isn't threadsafe or serializable, even if {@code
	 * unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered map's methods, such as {@code size()}, iterate across
	 * every key/value mapping in the underlying map and determine which satisfy the
	 * filter. When a live view is <i>not</i> needed, it may be faster to copy the
	 * filtered map 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.
	 */
	public static <K, V> Map<K, V> filterValues(Map<K, V> unfiltered, final Predicate<? super V> valuePredicate) {
		if (unfiltered instanceof SortedMap) {
			return filterValues((SortedMap<K, V>) unfiltered, valuePredicate);
		} else if (unfiltered instanceof BiMap) {
			return filterValues((BiMap<K, V>) unfiltered, valuePredicate);
		}
		return filterEntries(unfiltered, Maps.<V>valuePredicateOnEntries(valuePredicate));
	}

	/**
	 * Returns a sorted map containing the mappings in {@code unfiltered} whose
	 * values satisfy a predicate. The returned map is a live view of {@code
	 * unfiltered}; changes to one affect the other.
	 *
	 * <p>
	 * The resulting map's {@code keySet()}, {@code entrySet()}, and {@code
	 * values()} views have iterators that don't support {@code remove()}, but all
	 * other methods are supported by the map and its views. When given a value that
	 * doesn't satisfy the predicate, the map's {@code put()}, {@code
	 * putAll()}, and {@link Entry#setValue} methods throw an
	 * {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered map or its views, only mappings whose values satisfy the filter
	 * will be removed from the underlying map.
	 *
	 * <p>
	 * The returned map isn't threadsafe or serializable, even if {@code
	 * unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered map's methods, such as {@code size()}, iterate across
	 * every key/value mapping in the underlying map and determine which satisfy the
	 * filter. When a live view is <i>not</i> needed, it may be faster to copy the
	 * filtered map 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> SortedMap<K, V> filterValues(SortedMap<K, V> unfiltered,
			final Predicate<? super V> valuePredicate) {
		return filterEntries(unfiltered, Maps.<V>valuePredicateOnEntries(valuePredicate));
	}

	/**
	 * Returns a navigable map containing the mappings in {@code unfiltered} whose
	 * values satisfy a predicate. The returned map is a live view of {@code
	 * unfiltered}; changes to one affect the other.
	 *
	 * <p>
	 * The resulting map's {@code keySet()}, {@code entrySet()}, and {@code
	 * values()} views have iterators that don't support {@code remove()}, but all
	 * other methods are supported by the map and its views. When given a value that
	 * doesn't satisfy the predicate, the map's {@code put()}, {@code
	 * putAll()}, and {@link Entry#setValue} methods throw an
	 * {@link IllegalArgumentException}.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered map or its views, only mappings whose values satisfy the filter
	 * will be removed from the underlying map.
	 *
	 * <p>
	 * The returned map isn't threadsafe or serializable, even if {@code
	 * unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered map's methods, such as {@code size()}, iterate across
	 * every key/value mapping in the underlying map and determine which satisfy the
	 * filter. When a live view is <i>not</i> needed, it may be faster to copy the
	 * filtered map 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
	 */
	@GwtIncompatible("NavigableMap")
	public static <K, V> NavigableMap<K, V> filterValues(NavigableMap<K, V> unfiltered,
			final Predicate<? super V> valuePredicate) {
		return filterEntries(unfiltered, Maps.<V>valuePredicateOnEntries(valuePredicate));
	}

	/**
	 * Returns a bimap containing the mappings in {@code unfiltered} whose values
	 * satisfy a predicate. The returned bimap is a live view of {@code unfiltered};
	 * changes to one affect the other.
	 *
	 * <p>
	 * The resulting bimap's {@code keySet()}, {@code entrySet()}, and
	 * {@code values()} views have iterators that don't support {@code remove()},
	 * but all other methods are supported by the bimap and its views. When given a
	 * value that doesn't satisfy the predicate, the bimap's {@code put()},
	 * {@code forcePut()} and {@code putAll()} methods throw an
	 * {@link IllegalArgumentException}. Similarly, the map's entries have a
	 * {@link Entry#setValue} method that throws an {@link IllegalArgumentException}
	 * when the provided value doesn't satisfy the predicate.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered bimap or its views, only mappings that satisfy the filter will
	 * be removed from the underlying bimap.
	 *
	 * <p>
	 * The returned bimap isn't threadsafe or serializable, even if
	 * {@code unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered bimap's methods, such as {@code size()}, iterate across
	 * every value in the underlying bimap and determine which satisfy the filter.
	 * When a live view is <i>not</i> needed, it may be faster to copy the filtered
	 * bimap 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> BiMap<K, V> filterValues(BiMap<K, V> unfiltered, final Predicate<? super V> valuePredicate) {
		return filterEntries(unfiltered, Maps.<V>valuePredicateOnEntries(valuePredicate));
	}

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

	/**
	 * Returns a sorted map containing the mappings in {@code unfiltered} that
	 * satisfy a predicate. The returned map is a live view of {@code unfiltered};
	 * changes to one affect the other.
	 *
	 * <p>
	 * The resulting map's {@code keySet()}, {@code entrySet()}, and {@code
	 * values()} views have iterators that don't support {@code remove()}, but all
	 * other methods are supported by the map and its views. When given a key/value
	 * pair that doesn't satisfy the predicate, the map's {@code put()} and
	 * {@code putAll()} methods throw an {@link IllegalArgumentException}.
	 * Similarly, the map's entries have a {@link Entry#setValue} method that throws
	 * an {@link IllegalArgumentException} when the existing key and the provided
	 * value don't satisfy the predicate.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered map or its views, only mappings that satisfy the filter will be
	 * removed from the underlying map.
	 *
	 * <p>
	 * The returned map isn't threadsafe or serializable, even if {@code
	 * unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered map's methods, such as {@code size()}, iterate across
	 * every key/value mapping in the underlying map and determine which satisfy the
	 * filter. When a live view is <i>not</i> needed, it may be faster to copy the
	 * filtered map 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> SortedMap<K, V> filterEntries(SortedMap<K, V> unfiltered,
			Predicate<? super Entry<K, V>> entryPredicate) {
		return Platform.mapsFilterSortedMap(unfiltered, entryPredicate);
	}

	static <K, V> SortedMap<K, V> filterSortedIgnoreNavigable(SortedMap<K, V> unfiltered,
			Predicate<? super Entry<K, V>> entryPredicate) {
		checkNotNull(entryPredicate);
		return (unfiltered instanceof FilteredEntrySortedMap)
				? filterFiltered((FilteredEntrySortedMap<K, V>) unfiltered, entryPredicate)
				: new FilteredEntrySortedMap<K, V>(checkNotNull(unfiltered), entryPredicate);
	}

	/**
	 * Returns a sorted map containing the mappings in {@code unfiltered} that
	 * satisfy a predicate. The returned map is a live view of {@code unfiltered};
	 * changes to one affect the other.
	 *
	 * <p>
	 * The resulting map's {@code keySet()}, {@code entrySet()}, and {@code
	 * values()} views have iterators that don't support {@code remove()}, but all
	 * other methods are supported by the map and its views. When given a key/value
	 * pair that doesn't satisfy the predicate, the map's {@code put()} and
	 * {@code putAll()} methods throw an {@link IllegalArgumentException}.
	 * Similarly, the map's entries have a {@link Entry#setValue} method that throws
	 * an {@link IllegalArgumentException} when the existing key and the provided
	 * value don't satisfy the predicate.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered map or its views, only mappings that satisfy the filter will be
	 * removed from the underlying map.
	 *
	 * <p>
	 * The returned map isn't threadsafe or serializable, even if {@code
	 * unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered map's methods, such as {@code size()}, iterate across
	 * every key/value mapping in the underlying map and determine which satisfy the
	 * filter. When a live view is <i>not</i> needed, it may be faster to copy the
	 * filtered map 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
	 */
	@GwtIncompatible("NavigableMap")
	public static <K, V> NavigableMap<K, V> filterEntries(NavigableMap<K, V> unfiltered,
			Predicate<? super Entry<K, V>> entryPredicate) {
		checkNotNull(entryPredicate);
		return (unfiltered instanceof FilteredEntryNavigableMap)
				? filterFiltered((FilteredEntryNavigableMap<K, V>) unfiltered, entryPredicate)
				: new FilteredEntryNavigableMap<K, V>(checkNotNull(unfiltered), entryPredicate);
	}

	/**
	 * Returns a bimap containing the mappings in {@code unfiltered} that satisfy a
	 * predicate. The returned bimap is a live view of {@code unfiltered}; changes
	 * to one affect the other.
	 *
	 * <p>
	 * The resulting bimap's {@code keySet()}, {@code entrySet()}, and
	 * {@code values()} views have iterators that don't support {@code remove()},
	 * but all other methods are supported by the bimap and its views. When given a
	 * key/value pair that doesn't satisfy the predicate, the bimap's {@code put()},
	 * {@code forcePut()} and {@code putAll()} methods throw an
	 * {@link IllegalArgumentException}. Similarly, the map's entries have an
	 * {@link Entry#setValue} method that throws an {@link IllegalArgumentException}
	 * when the existing key and the provided value don't satisfy the predicate.
	 *
	 * <p>
	 * When methods such as {@code removeAll()} and {@code clear()} are called on
	 * the filtered bimap or its views, only mappings that satisfy the filter will
	 * be removed from the underlying bimap.
	 *
	 * <p>
	 * The returned bimap isn't threadsafe or serializable, even if
	 * {@code unfiltered} is.
	 *
	 * <p>
	 * Many of the filtered bimap's methods, such as {@code size()}, iterate across
	 * every key/value mapping in the underlying bimap and determine which satisfy
	 * the filter. When a live view is <i>not</i> needed, it may be faster to copy
	 * the filtered bimap 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> BiMap<K, V> filterEntries(BiMap<K, V> unfiltered,
			Predicate<? super Entry<K, V>> entryPredicate) {
		checkNotNull(unfiltered);
		checkNotNull(entryPredicate);
		return (unfiltered instanceof FilteredEntryBiMap)
				? filterFiltered((FilteredEntryBiMap<K, V>) unfiltered, entryPredicate)
				: new FilteredEntryBiMap<K, V>(unfiltered, entryPredicate);
	}

	/**
	 * Support {@code clear()}, {@code removeAll()}, and {@code retainAll()} when
	 * filtering a filtered map.
	 */
	private static <K, V> Map<K, V> filterFiltered(AbstractFilteredMap<K, V> map,
			Predicate<? super Entry<K, V>> entryPredicate) {
		return new FilteredEntryMap<K, V>(map.unfiltered, Predicates.<Entry<K, V>>and(map.predicate, entryPredicate));
	}

	private abstract static class AbstractFilteredMap<K, V> extends ImprovedAbstractMap<K, V> {
		final Map<K, V> unfiltered;
		final Predicate<? super Entry<K, V>> predicate;

		AbstractFilteredMap(Map<K, V> unfiltered, Predicate<? super Entry<K, V>> predicate) {
			this.unfiltered = unfiltered;
			this.predicate = predicate;
		}

		boolean apply(@Nullable Object key, @Nullable V value) {
			// This method is called only when the key is in the map, implying that
			// key is a K.
			@SuppressWarnings("unchecked")
			K k = (K) key;
			return predicate.apply(Maps.immutableEntry(k, value));
		}

		@Override
		public V put(K key, V value) {
			checkArgument(apply(key, value));
			return unfiltered.put(key, value);
		}

		@Override
		public void putAll(Map<? extends K, ? extends V> map) {
			for (Entry<? extends K, ? extends V> entry : map.entrySet()) {
				checkArgument(apply(entry.getKey(), entry.getValue()));
			}
			unfiltered.putAll(map);
		}

		@Override
		public boolean containsKey(Object key) {
			return unfiltered.containsKey(key) && apply(key, unfiltered.get(key));
		}

		@Override
		public V get(Object key) {
			V value = unfiltered.get(key);
			return ((value != null) && apply(key, value)) ? value : null;
		}

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

		@Override
		public V remove(Object key) {
			return containsKey(key) ? unfiltered.remove(key) : null;
		}

		@Override
		Collection<V> createValues() {
			return new FilteredMapValues<K, V>(this, unfiltered, predicate);
		}
	}

	private static final class FilteredMapValues<K, V> extends Maps.Values<K, V> {
		Map<K, V> unfiltered;
		Predicate<? super Entry<K, V>> predicate;

		FilteredMapValues(Map<K, V> filteredMap, Map<K, V> unfiltered, Predicate<? super Entry<K, V>> predicate) {
			super(filteredMap);
			this.unfiltered = unfiltered;
			this.predicate = predicate;
		}

		@Override
		public boolean remove(Object o) {
			return Iterables.removeFirstMatching(unfiltered.entrySet(),
					Predicates.<Entry<K, V>>and(predicate, Maps.<V>valuePredicateOnEntries(equalTo(o)))) != null;
		}

		private boolean removeIf(Predicate<? super V> valuePredicate) {
			return Iterables.removeIf(unfiltered.entrySet(),
					Predicates.<Entry<K, V>>and(predicate, Maps.<V>valuePredicateOnEntries(valuePredicate)));
		}

		@Override
		public boolean removeAll(Collection<?> collection) {
			return removeIf(in(collection));
		}

		@Override
		public boolean retainAll(Collection<?> collection) {
			return removeIf(not(in(collection)));
		}

		@Override
		public Object[] toArray() {
			// creating an ArrayList so filtering happens once
			return Lists.newArrayList(iterator()).toArray();
		}

		@Override
		public <T> T[] toArray(T[] array) {
			return Lists.newArrayList(iterator()).toArray(array);
		}
	}

	private static class FilteredKeyMap<K, V> extends AbstractFilteredMap<K, V> {
		Predicate<? super K> keyPredicate;

		FilteredKeyMap(Map<K, V> unfiltered, Predicate<? super K> keyPredicate,
				Predicate<? super Entry<K, V>> entryPredicate) {
			super(unfiltered, entryPredicate);
			this.keyPredicate = keyPredicate;
		}

		@Override
		protected Set<Entry<K, V>> createEntrySet() {
			return Sets.filter(unfiltered.entrySet(), predicate);
		}

		@Override
		Set<K> createKeySet() {
			return Sets.filter(unfiltered.keySet(), keyPredicate);
		}

		// The cast is called only when the key is in the unfiltered map, implying
		// that key is a K.
		@Override
		@SuppressWarnings("unchecked")
		public boolean containsKey(Object key) {
			return unfiltered.containsKey(key) && keyPredicate.apply((K) key);
		}
	}

	static class FilteredEntryMap<K, V> extends AbstractFilteredMap<K, V> {
		/**
		 * Entries in this set satisfy the predicate, but they don't validate the input
		 * to {@code Entry.setValue()}.
		 */
		final Set<Entry<K, V>> filteredEntrySet;

		FilteredEntryMap(Map<K, V> unfiltered, Predicate<? super Entry<K, V>> entryPredicate) {
			super(unfiltered, entryPredicate);
			filteredEntrySet = Sets.filter(unfiltered.entrySet(), predicate);
		}

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

		private class EntrySet extends ForwardingSet<Entry<K, V>> {
			@Override
			protected Set<Entry<K, V>> delegate() {
				return filteredEntrySet;
			}

			@Override
			public Iterator<Entry<K, V>> iterator() {
				return new TransformedIterator<Entry<K, V>, Entry<K, V>>(filteredEntrySet.iterator()) {
					@Override
					Entry<K, V> transform(final Entry<K, V> entry) {
						return new ForwardingMapEntry<K, V>() {
							@Override
							protected Entry<K, V> delegate() {
								return entry;
							}

							@Override
							public V setValue(V newValue) {
								checkArgument(apply(getKey(), newValue));
								return super.setValue(newValue);
							}
						};
					}
				};
			}
		}

		@Override
		Set<K> createKeySet() {
			return new KeySet();
		}

		class KeySet extends Maps.KeySet<K, V> {
			KeySet() {
				super(FilteredEntryMap.this);
			}

			@Override
			public boolean remove(Object o) {
				if (containsKey(o)) {
					unfiltered.remove(o);
					return true;
				}
				return false;
			}

			private boolean removeIf(Predicate<? super K> keyPredicate) {
				return Iterables.removeIf(unfiltered.entrySet(),
						Predicates.<Entry<K, V>>and(predicate, Maps.<K>keyPredicateOnEntries(keyPredicate)));
			}

			@Override
			public boolean removeAll(Collection<?> c) {
				return removeIf(in(c));
			}

			@Override
			public boolean retainAll(Collection<?> c) {
				return removeIf(not(in(c)));
			}

			@Override
			public Object[] toArray() {
				// creating an ArrayList so filtering happens once
				return Lists.newArrayList(iterator()).toArray();
			}

			@Override
			public <T> T[] toArray(T[] array) {
				return Lists.newArrayList(iterator()).toArray(array);
			}
		}
	}

	/**
	 * Support {@code clear()}, {@code removeAll()}, and {@code retainAll()} when
	 * filtering a filtered sorted map.
	 */
	private static <K, V> SortedMap<K, V> filterFiltered(FilteredEntrySortedMap<K, V> map,
			Predicate<? super Entry<K, V>> entryPredicate) {
		Predicate<Entry<K, V>> predicate = Predicates.and(map.predicate, entryPredicate);
		return new FilteredEntrySortedMap<K, V>(map.sortedMap(), predicate);
	}

	private static class FilteredEntrySortedMap<K, V> extends FilteredEntryMap<K, V> implements SortedMap<K, V> {

		FilteredEntrySortedMap(SortedMap<K, V> unfiltered, Predicate<? super Entry<K, V>> entryPredicate) {
			super(unfiltered, entryPredicate);
		}

		SortedMap<K, V> sortedMap() {
			return (SortedMap<K, V>) unfiltered;
		}

		@Override
		public SortedSet<K> keySet() {
			return (SortedSet<K>) super.keySet();
		}

		@Override
		SortedSet<K> createKeySet() {
			return new SortedKeySet();
		}

		class SortedKeySet extends KeySet implements SortedSet<K> {
			@Override
			public Comparator<? super K> comparator() {
				return sortedMap().comparator();
			}

			@Override
			public SortedSet<K> subSet(K fromElement, K toElement) {
				return (SortedSet<K>) subMap(fromElement, toElement).keySet();
			}

			@Override
			public SortedSet<K> headSet(K toElement) {
				return (SortedSet<K>) headMap(toElement).keySet();
			}

			@Override
			public SortedSet<K> tailSet(K fromElement) {
				return (SortedSet<K>) tailMap(fromElement).keySet();
			}

			@Override
			public K first() {
				return firstKey();
			}

			@Override
			public K last() {
				return lastKey();
			}
		}

		@Override
		public Comparator<? super K> comparator() {
			return sortedMap().comparator();
		}

		@Override
		public K firstKey() {
			// correctly throws NoSuchElementException when filtered map is empty.
			return keySet().iterator().next();
		}

		@Override
		public K lastKey() {
			SortedMap<K, V> headMap = sortedMap();
			while (true) {
				// correctly throws NoSuchElementException when filtered map is empty.
				K key = headMap.lastKey();
				if (apply(key, unfiltered.get(key))) {
					return key;
				}
				headMap = sortedMap().headMap(key);
			}
		}

		@Override
		public SortedMap<K, V> headMap(K toKey) {
			return new FilteredEntrySortedMap<K, V>(sortedMap().headMap(toKey), predicate);
		}

		@Override
		public SortedMap<K, V> subMap(K fromKey, K toKey) {
			return new FilteredEntrySortedMap<K, V>(sortedMap().subMap(fromKey, toKey), predicate);
		}

		@Override
		public SortedMap<K, V> tailMap(K fromKey) {
			return new FilteredEntrySortedMap<K, V>(sortedMap().tailMap(fromKey), predicate);
		}
	}

	/**
	 * Support {@code clear()}, {@code removeAll()}, and {@code retainAll()} when
	 * filtering a filtered navigable map.
	 */
	@GwtIncompatible("NavigableMap")
	private static <K, V> NavigableMap<K, V> filterFiltered(FilteredEntryNavigableMap<K, V> map,
			Predicate<? super Entry<K, V>> entryPredicate) {
		Predicate<Entry<K, V>> predicate = Predicates.and(map.entryPredicate, entryPredicate);
		return new FilteredEntryNavigableMap<K, V>(map.unfiltered, predicate);
	}

	@GwtIncompatible("NavigableMap")
	private static class FilteredEntryNavigableMap<K, V> extends AbstractNavigableMap<K, V> {
		/*
		 * It's less code to extend AbstractNavigableMap and forward the filtering logic
		 * to FilteredEntryMap than to extend FilteredEntrySortedMap and reimplement all
		 * the NavigableMap methods.
		 */

		private final NavigableMap<K, V> unfiltered;
		private final Predicate<? super Entry<K, V>> entryPredicate;
		private final Map<K, V> filteredDelegate;

		FilteredEntryNavigableMap(NavigableMap<K, V> unfiltered, Predicate<? super Entry<K, V>> entryPredicate) {
			this.unfiltered = checkNotNull(unfiltered);
			this.entryPredicate = entryPredicate;
			this.filteredDelegate = new FilteredEntryMap<K, V>(unfiltered, entryPredicate);
		}

		@Override
		public Comparator<? super K> comparator() {
			return unfiltered.comparator();
		}

		@Override
		public NavigableSet<K> navigableKeySet() {
			return new Maps.NavigableKeySet<K, V>(this) {
				@Override
				public boolean removeAll(Collection<?> c) {
					return Iterators.removeIf(unfiltered.entrySet().iterator(),
							Predicates.<Entry<K, V>>and(entryPredicate, Maps.<K>keyPredicateOnEntries(in(c))));
				}

				@Override
				public boolean retainAll(Collection<?> c) {
					return Iterators.removeIf(unfiltered.entrySet().iterator(),
							Predicates.<Entry<K, V>>and(entryPredicate, Maps.<K>keyPredicateOnEntries(not(in(c)))));
				}
			};
		}

		@Override
		public Collection<V> values() {
			return new FilteredMapValues<K, V>(this, unfiltered, entryPredicate);
		}

		@Override
		Iterator<Entry<K, V>> entryIterator() {
			return Iterators.filter(unfiltered.entrySet().iterator(), entryPredicate);
		}

		@Override
		Iterator<Entry<K, V>> descendingEntryIterator() {
			return Iterators.filter(unfiltered.descendingMap().entrySet().iterator(), entryPredicate);
		}

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

		@Override
		@Nullable
		public V get(@Nullable Object key) {
			return filteredDelegate.get(key);
		}

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

		@Override
		public V put(K key, V value) {
			return filteredDelegate.put(key, value);
		}

		@Override
		public V remove(@Nullable Object key) {
			return filteredDelegate.remove(key);
		}

		@Override
		public void putAll(Map<? extends K, ? extends V> m) {
			filteredDelegate.putAll(m);
		}

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

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

		@Override
		public Entry<K, V> pollFirstEntry() {
			return Iterables.removeFirstMatching(unfiltered.entrySet(), entryPredicate);
		}

		@Override
		public Entry<K, V> pollLastEntry() {
			return Iterables.removeFirstMatching(unfiltered.descendingMap().entrySet(), entryPredicate);
		}

		@Override
		public NavigableMap<K, V> descendingMap() {
			return filterEntries(unfiltered.descendingMap(), entryPredicate);
		}

		@Override
		public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
			return filterEntries(unfiltered.subMap(fromKey, fromInclusive, toKey, toInclusive), entryPredicate);
		}

		@Override
		public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
			return filterEntries(unfiltered.headMap(toKey, inclusive), entryPredicate);
		}

		@Override
		public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
			return filterEntries(unfiltered.tailMap(fromKey, inclusive), entryPredicate);
		}
	}

	/**
	 * Support {@code clear()}, {@code removeAll()}, and {@code retainAll()} when
	 * filtering a filtered map.
	 */
	private static <K, V> BiMap<K, V> filterFiltered(FilteredEntryBiMap<K, V> map,
			Predicate<? super Entry<K, V>> entryPredicate) {
		Predicate<Entry<K, V>> predicate = Predicates.and(map.predicate, entryPredicate);
		return new FilteredEntryBiMap<K, V>(map.unfiltered(), predicate);
	}

	static final class FilteredEntryBiMap<K, V> extends FilteredEntryMap<K, V> implements BiMap<K, V> {
		private final BiMap<V, K> inverse;

		private static <K, V> Predicate<Entry<V, K>> inversePredicate(
				final Predicate<? super Entry<K, V>> forwardPredicate) {
			return new Predicate<Entry<V, K>>() {
				@Override
				public boolean apply(Entry<V, K> input) {
					return forwardPredicate.apply(Maps.immutableEntry(input.getValue(), input.getKey()));
				}
			};
		}

		FilteredEntryBiMap(BiMap<K, V> delegate, Predicate<? super Entry<K, V>> predicate) {
			super(delegate, predicate);
			this.inverse = new FilteredEntryBiMap<V, K>(delegate.inverse(), inversePredicate(predicate), this);
		}

		private FilteredEntryBiMap(BiMap<K, V> delegate, Predicate<? super Entry<K, V>> predicate,
				BiMap<V, K> inverse) {
			super(delegate, predicate);
			this.inverse = inverse;
		}

		BiMap<K, V> unfiltered() {
			return (BiMap<K, V>) unfiltered;
		}

		@Override
		public V forcePut(@Nullable K key, @Nullable V value) {
			checkArgument(apply(key, value));
			return unfiltered().forcePut(key, value);
		}

		@Override
		public BiMap<V, K> inverse() {
			return inverse;
		}

		@Override
		public Set<V> values() {
			return inverse.keySet();
		}
	}

	/**
	 * Returns an unmodifiable view of the specified navigable map. Query operations
	 * on the returned map read through to the specified map, and attempts to modify
	 * the returned map, whether direct or via its views, result in an
	 * {@code UnsupportedOperationException}.
	 *
	 * <p>
	 * The returned navigable map will be serializable if the specified navigable
	 * map is serializable.
	 *
	 * @param map the navigable map for which an unmodifiable view is to be returned
	 * @return an unmodifiable view of the specified navigable map
	 * @since 12.0
	 */
	@GwtIncompatible("NavigableMap")
	public static <K, V> NavigableMap<K, V> unmodifiableNavigableMap(NavigableMap<K, V> map) {
		checkNotNull(map);
		if (map instanceof UnmodifiableNavigableMap) {
			return map;
		} else {
			return new UnmodifiableNavigableMap<K, V>(map);
		}
	}

	@Nullable
	private static <K, V> Entry<K, V> unmodifiableOrNull(@Nullable Entry<K, V> entry) {
		return (entry == null) ? null : Maps.unmodifiableEntry(entry);
	}

	@GwtIncompatible("NavigableMap")
	static class UnmodifiableNavigableMap<K, V> extends ForwardingSortedMap<K, V>
			implements NavigableMap<K, V>, Serializable {
		private final NavigableMap<K, V> delegate;

		UnmodifiableNavigableMap(NavigableMap<K, V> delegate) {
			this.delegate = delegate;
		}

		UnmodifiableNavigableMap(NavigableMap<K, V> delegate, UnmodifiableNavigableMap<K, V> descendingMap) {
			this.delegate = delegate;
			this.descendingMap = descendingMap;
		}

		@Override
		protected SortedMap<K, V> delegate() {
			return Collections.unmodifiableSortedMap(delegate);
		}

		@Override
		public Entry<K, V> lowerEntry(K key) {
			return unmodifiableOrNull(delegate.lowerEntry(key));
		}

		@Override
		public K lowerKey(K key) {
			return delegate.lowerKey(key);
		}

		@Override
		public Entry<K, V> floorEntry(K key) {
			return unmodifiableOrNull(delegate.floorEntry(key));
		}

		@Override
		public K floorKey(K key) {
			return delegate.floorKey(key);
		}

		@Override
		public Entry<K, V> ceilingEntry(K key) {
			return unmodifiableOrNull(delegate.ceilingEntry(key));
		}

		@Override
		public K ceilingKey(K key) {
			return delegate.ceilingKey(key);
		}

		@Override
		public Entry<K, V> higherEntry(K key) {
			return unmodifiableOrNull(delegate.higherEntry(key));
		}

		@Override
		public K higherKey(K key) {
			return delegate.higherKey(key);
		}

		@Override
		public Entry<K, V> firstEntry() {
			return unmodifiableOrNull(delegate.firstEntry());
		}

		@Override
		public Entry<K, V> lastEntry() {
			return unmodifiableOrNull(delegate.lastEntry());
		}

		@Override
		public final Entry<K, V> pollFirstEntry() {
			throw new UnsupportedOperationException();
		}

		@Override
		public final Entry<K, V> pollLastEntry() {
			throw new UnsupportedOperationException();
		}

		private transient UnmodifiableNavigableMap<K, V> descendingMap;

		@Override
		public NavigableMap<K, V> descendingMap() {
			UnmodifiableNavigableMap<K, V> result = descendingMap;
			return (result == null) ? descendingMap = new UnmodifiableNavigableMap<K, V>(delegate.descendingMap(), this)
					: result;
		}

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

		@Override
		public NavigableSet<K> navigableKeySet() {
			return Sets.unmodifiableNavigableSet(delegate.navigableKeySet());
		}

		@Override
		public NavigableSet<K> descendingKeySet() {
			return Sets.unmodifiableNavigableSet(delegate.descendingKeySet());
		}

		@Override
		public SortedMap<K, V> subMap(K fromKey, K toKey) {
			return subMap(fromKey, true, toKey, false);
		}

		@Override
		public SortedMap<K, V> headMap(K toKey) {
			return headMap(toKey, false);
		}

		@Override
		public SortedMap<K, V> tailMap(K fromKey) {
			return tailMap(fromKey, true);
		}

		@Override
		public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
			return Maps.unmodifiableNavigableMap(delegate.subMap(fromKey, fromInclusive, toKey, toInclusive));
		}

		@Override
		public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
			return Maps.unmodifiableNavigableMap(delegate.headMap(toKey, inclusive));
		}

		@Override
		public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
			return Maps.unmodifiableNavigableMap(delegate.tailMap(fromKey, inclusive));
		}
	}

	/**
	 * Returns a synchronized (thread-safe) navigable map backed by the specified
	 * navigable map. In order to guarantee serial access, it is critical that
	 * <b>all</b> access to the backing navigable map is accomplished through the
	 * returned navigable map (or its views).
	 *
	 * <p>
	 * It is imperative that the user manually synchronize on the returned navigable
	 * map when iterating over any of its collection views, or the collections views
	 * of any of its {@code descendingMap}, {@code subMap}, {@code headMap} or
	 * {@code tailMap} views.
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	NavigableMap<K, V> map = synchronizedNavigableMap(new TreeMap<K, V>());
	 *
	 * 	// Needn't be in synchronized block
	 * 	NavigableSet<K> set = map.navigableKeySet();
	 *
	 * 	synchronized (map) { // Synchronizing on map, not set!
	 * 		Iterator<K> it = set.iterator(); // Must be in synchronized block
	 * 		while (it.hasNext()) {
	 * 			foo(it.next());
	 * 		}
	 * 	}
	 * }
	 * </pre>
	 *
	 * <p>
	 * or:
	 * 
	 * <pre>
	 * {
	 * 	&#64;code
	 *
	 * 	NavigableMap<K, V> map = synchronizedNavigableMap(new TreeMap<K, V>());
	 * 	NavigableMap<K, V> map2 = map.subMap(foo, false, bar, true);
	 *
	 * 	// Needn't be in synchronized block
	 * 	NavigableSet<K> set2 = map2.descendingKeySet();
	 *
	 * 	synchronized (map) { // Synchronizing on map, not map2 or set2!
	 * 		Iterator<K> it = set2.iterator(); // Must be in synchronized block
	 * 		while (it.hasNext()) {
	 * 			foo(it.next());
	 * 		}
	 * 	}
	 * }
	 * </pre>
	 *
	 * <p>
	 * Failure to follow this advice may result in non-deterministic behavior.
	 *
	 * <p>
	 * The returned navigable map will be serializable if the specified navigable
	 * map is serializable.
	 *
	 * @param navigableMap the navigable map to be "wrapped" in a synchronized
	 *                     navigable map.
	 * @return a synchronized view of the specified navigable map.
	 * @since 13.0
	 */
	@GwtIncompatible("NavigableMap")
	public static <K, V> NavigableMap<K, V> synchronizedNavigableMap(NavigableMap<K, V> navigableMap) {
		return Synchronized.navigableMap(navigableMap);
	}

	/**
	 * {@code AbstractMap} extension that implements {@link #isEmpty()} as {@code
	 * entrySet().isEmpty()} instead of {@code size() == 0} to speed up
	 * implementations where {@code size()} is O(n), and it delegates the {@code
	 * isEmpty()} methods of its key set and value collection to this
	 * implementation.
	 */
	@GwtCompatible
	abstract static class ImprovedAbstractMap<K, V> extends AbstractMap<K, V> {
		/**
		 * Creates the entry set to be returned by {@link #entrySet()}. This method is
		 * invoked at most once on a given map, at the time when {@code entrySet} is
		 * first called.
		 */
		abstract Set<Entry<K, V>> createEntrySet();

		private transient Set<Entry<K, V>> entrySet;

		@Override
		public Set<Entry<K, V>> entrySet() {
			Set<Entry<K, V>> result = entrySet;
			return (result == null) ? entrySet = createEntrySet() : result;
		}

		private transient Set<K> keySet;

		@Override
		public Set<K> keySet() {
			Set<K> result = keySet;
			return (result == null) ? keySet = createKeySet() : result;
		}

		Set<K> createKeySet() {
			return new KeySet<K, V>(this);
		}

		private transient Collection<V> values;

		@Override
		public Collection<V> values() {
			Collection<V> result = values;
			return (result == null) ? values = createValues() : result;
		}

		Collection<V> createValues() {
			return new Values<K, V>(this);
		}
	}

	/**
	 * Delegates to {@link Map#get}. Returns {@code null} on {@code
	 * ClassCastException} and {@code NullPointerException}.
	 */
	static <V> V safeGet(Map<?, V> map, @Nullable Object key) {
		checkNotNull(map);
		try {
			return map.get(key);
		} catch (ClassCastException e) {
			return null;
		} catch (NullPointerException e) {
			return null;
		}
	}

	/**
	 * Delegates to {@link Map#containsKey}. Returns {@code false} on {@code
	 * ClassCastException} and {@code NullPointerException}.
	 */
	static boolean safeContainsKey(Map<?, ?> map, Object key) {
		checkNotNull(map);
		try {
			return map.containsKey(key);
		} catch (ClassCastException e) {
			return false;
		} catch (NullPointerException e) {
			return false;
		}
	}

	/**
	 * Delegates to {@link Map#remove}. Returns {@code null} on {@code
	 * ClassCastException} and {@code NullPointerException}.
	 */
	static <V> V safeRemove(Map<?, V> map, Object key) {
		checkNotNull(map);
		try {
			return map.remove(key);
		} catch (ClassCastException e) {
			return null;
		} catch (NullPointerException e) {
			return null;
		}
	}

	/**
	 * An admittedly inefficient implementation of {@link Map#containsKey}.
	 */
	static boolean containsKeyImpl(Map<?, ?> map, @Nullable Object key) {
		return Iterators.contains(keyIterator(map.entrySet().iterator()), key);
	}

	/**
	 * An implementation of {@link Map#containsValue}.
	 */
	static boolean containsValueImpl(Map<?, ?> map, @Nullable Object value) {
		return Iterators.contains(valueIterator(map.entrySet().iterator()), value);
	}

	/**
	 * Implements {@code Collection.contains} safely for forwarding collections of
	 * map entries. If {@code o} is an instance of {@code Map.Entry}, it is wrapped
	 * using {@link #unmodifiableEntry} to protect against a possible nefarious
	 * equals method.
	 *
	 * <p>
	 * Note that {@code c} is the backing (delegate) collection, rather than the
	 * forwarding collection.
	 *
	 * @param c the delegate (unwrapped) collection of map entries
	 * @param o the object that might be contained in {@code c}
	 * @return {@code true} if {@code c} contains {@code o}
	 */
	static <K, V> boolean containsEntryImpl(Collection<Entry<K, V>> c, Object o) {
		if (!(o instanceof Entry)) {
			return false;
		}
		return c.contains(unmodifiableEntry((Entry<?, ?>) o));
	}

	/**
	 * Implements {@code Collection.remove} safely for forwarding collections of map
	 * entries. If {@code o} is an instance of {@code Map.Entry}, it is wrapped
	 * using {@link #unmodifiableEntry} to protect against a possible nefarious
	 * equals method.
	 *
	 * <p>
	 * Note that {@code c} is backing (delegate) collection, rather than the
	 * forwarding collection.
	 *
	 * @param c the delegate (unwrapped) collection of map entries
	 * @param o the object to remove from {@code c}
	 * @return {@code true} if {@code c} was changed
	 */
	static <K, V> boolean removeEntryImpl(Collection<Entry<K, V>> c, Object o) {
		if (!(o instanceof Entry)) {
			return false;
		}
		return c.remove(unmodifiableEntry((Entry<?, ?>) o));
	}

	/**
	 * An implementation of {@link Map#equals}.
	 */
	static boolean equalsImpl(Map<?, ?> map, Object object) {
		if (map == object) {
			return true;
		} else if (object instanceof Map) {
			Map<?, ?> o = (Map<?, ?>) object;
			return map.entrySet().equals(o.entrySet());
		}
		return false;
	}

	static final MapJoiner STANDARD_JOINER = Collections2.STANDARD_JOINER.withKeyValueSeparator("=");

	/**
	 * An implementation of {@link Map#toString}.
	 */
	static String toStringImpl(Map<?, ?> map) {
		StringBuilder sb = Collections2.newStringBuilderForCollection(map.size()).append('{');
		STANDARD_JOINER.appendTo(sb, map);
		return sb.append('}').toString();
	}

	/**
	 * An implementation of {@link Map#putAll}.
	 */
	static <K, V> void putAllImpl(Map<K, V> self, Map<? extends K, ? extends V> map) {
		for (Map.Entry<? extends K, ? extends V> entry : map.entrySet()) {
			self.put(entry.getKey(), entry.getValue());
		}
	}

	static class KeySet<K, V> extends Sets.ImprovedAbstractSet<K> {
		final Map<K, V> map;

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

		Map<K, V> map() {
			return map;
		}

		@Override
		public Iterator<K> iterator() {
			return keyIterator(map().entrySet().iterator());
		}

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

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

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

		@Override
		public boolean remove(Object o) {
			if (contains(o)) {
				map().remove(o);
				return true;
			}
			return false;
		}

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

	@Nullable
	static <K> K keyOrNull(@Nullable Entry<K, ?> entry) {
		return (entry == null) ? null : entry.getKey();
	}

	@Nullable
	static <V> V valueOrNull(@Nullable Entry<?, V> entry) {
		return (entry == null) ? null : entry.getValue();
	}

	static class SortedKeySet<K, V> extends KeySet<K, V> implements SortedSet<K> {
		SortedKeySet(SortedMap<K, V> map) {
			super(map);
		}

		@Override
		SortedMap<K, V> map() {
			return (SortedMap<K, V>) super.map();
		}

		@Override
		public Comparator<? super K> comparator() {
			return map().comparator();
		}

		@Override
		public SortedSet<K> subSet(K fromElement, K toElement) {
			return new SortedKeySet<K, V>(map().subMap(fromElement, toElement));
		}

		@Override
		public SortedSet<K> headSet(K toElement) {
			return new SortedKeySet<K, V>(map().headMap(toElement));
		}

		@Override
		public SortedSet<K> tailSet(K fromElement) {
			return new SortedKeySet<K, V>(map().tailMap(fromElement));
		}

		@Override
		public K first() {
			return map().firstKey();
		}

		@Override
		public K last() {
			return map().lastKey();
		}
	}

	@GwtIncompatible("NavigableMap")
	static class NavigableKeySet<K, V> extends SortedKeySet<K, V> implements NavigableSet<K> {
		NavigableKeySet(NavigableMap<K, V> map) {
			super(map);
		}

		@Override
		NavigableMap<K, V> map() {
			return (NavigableMap<K, V>) map;
		}

		@Override
		public K lower(K e) {
			return map().lowerKey(e);
		}

		@Override
		public K floor(K e) {
			return map().floorKey(e);
		}

		@Override
		public K ceiling(K e) {
			return map().ceilingKey(e);
		}

		@Override
		public K higher(K e) {
			return map().higherKey(e);
		}

		@Override
		public K pollFirst() {
			return keyOrNull(map().pollFirstEntry());
		}

		@Override
		public K pollLast() {
			return keyOrNull(map().pollLastEntry());
		}

		@Override
		public NavigableSet<K> descendingSet() {
			return map().descendingKeySet();
		}

		@Override
		public Iterator<K> descendingIterator() {
			return descendingSet().iterator();
		}

		@Override
		public NavigableSet<K> subSet(K fromElement, boolean fromInclusive, K toElement, boolean toInclusive) {
			return map().subMap(fromElement, fromInclusive, toElement, toInclusive).navigableKeySet();
		}

		@Override
		public NavigableSet<K> headSet(K toElement, boolean inclusive) {
			return map().headMap(toElement, inclusive).navigableKeySet();
		}

		@Override
		public NavigableSet<K> tailSet(K fromElement, boolean inclusive) {
			return map().tailMap(fromElement, inclusive).navigableKeySet();
		}

		@Override
		public SortedSet<K> subSet(K fromElement, K toElement) {
			return subSet(fromElement, true, toElement, false);
		}

		@Override
		public SortedSet<K> headSet(K toElement) {
			return headSet(toElement, false);
		}

		@Override
		public SortedSet<K> tailSet(K fromElement) {
			return tailSet(fromElement, true);
		}
	}

	static class Values<K, V> extends AbstractCollection<V> {
		final Map<K, V> map;

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

		final Map<K, V> map() {
			return map;
		}

		@Override
		public Iterator<V> iterator() {
			return valueIterator(map().entrySet().iterator());
		}

		@Override
		public boolean remove(Object o) {
			try {
				return super.remove(o);
			} catch (UnsupportedOperationException e) {
				for (Entry<K, V> entry : map().entrySet()) {
					if (Objects.equal(o, entry.getValue())) {
						map().remove(entry.getKey());
						return true;
					}
				}
				return false;
			}
		}

		@Override
		public boolean removeAll(Collection<?> c) {
			try {
				return super.removeAll(checkNotNull(c));
			} catch (UnsupportedOperationException e) {
				Set<K> toRemove = Sets.newHashSet();
				for (Entry<K, V> entry : map().entrySet()) {
					if (c.contains(entry.getValue())) {
						toRemove.add(entry.getKey());
					}
				}
				return map().keySet().removeAll(toRemove);
			}
		}

		@Override
		public boolean retainAll(Collection<?> c) {
			try {
				return super.retainAll(checkNotNull(c));
			} catch (UnsupportedOperationException e) {
				Set<K> toRetain = Sets.newHashSet();
				for (Entry<K, V> entry : map().entrySet()) {
					if (c.contains(entry.getValue())) {
						toRetain.add(entry.getKey());
					}
				}
				return map().keySet().retainAll(toRetain);
			}
		}

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

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

		@Override
		public boolean contains(@Nullable Object o) {
			return map().containsValue(o);
		}

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

	abstract static class EntrySet<K, V> extends Sets.ImprovedAbstractSet<Entry<K, V>> {
		abstract Map<K, V> map();

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

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

		@Override
		public boolean contains(Object o) {
			if (o instanceof Entry) {
				Entry<?, ?> entry = (Entry<?, ?>) o;
				Object key = entry.getKey();
				V value = Maps.safeGet(map(), key);
				return Objects.equal(value, entry.getValue()) && (value != null || map().containsKey(key));
			}
			return false;
		}

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

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

		@Override
		public boolean removeAll(Collection<?> c) {
			try {
				return super.removeAll(checkNotNull(c));
			} catch (UnsupportedOperationException e) {
				// if the iterators don't support remove
				return Sets.removeAllImpl(this, c.iterator());
			}
		}

		@Override
		public boolean retainAll(Collection<?> c) {
			try {
				return super.retainAll(checkNotNull(c));
			} catch (UnsupportedOperationException e) {
				// if the iterators don't support remove
				Set<Object> keys = Sets.newHashSetWithExpectedSize(c.size());
				for (Object o : c) {
					if (contains(o)) {
						Entry<?, ?> entry = (Entry<?, ?>) o;
						keys.add(entry.getKey());
					}
				}
				return map().keySet().retainAll(keys);
			}
		}
	}

	@GwtIncompatible("NavigableMap")
	abstract static class DescendingMap<K, V> extends ForwardingMap<K, V> implements NavigableMap<K, V> {

		abstract NavigableMap<K, V> forward();

		@Override
		protected final Map<K, V> delegate() {
			return forward();
		}

		private transient Comparator<? super K> comparator;

		@SuppressWarnings("unchecked")
		@Override
		public Comparator<? super K> comparator() {
			Comparator<? super K> result = comparator;
			if (result == null) {
				Comparator<? super K> forwardCmp = forward().comparator();
				if (forwardCmp == null) {
					forwardCmp = (Comparator) Ordering.natural();
				}
				result = comparator = reverse(forwardCmp);
			}
			return result;
		}

		// If we inline this, we get a javac error.
		private static <T> Ordering<T> reverse(Comparator<T> forward) {
			return Ordering.from(forward).reverse();
		}

		@Override
		public K firstKey() {
			return forward().lastKey();
		}

		@Override
		public K lastKey() {
			return forward().firstKey();
		}

		@Override
		public Entry<K, V> lowerEntry(K key) {
			return forward().higherEntry(key);
		}

		@Override
		public K lowerKey(K key) {
			return forward().higherKey(key);
		}

		@Override
		public Entry<K, V> floorEntry(K key) {
			return forward().ceilingEntry(key);
		}

		@Override
		public K floorKey(K key) {
			return forward().ceilingKey(key);
		}

		@Override
		public Entry<K, V> ceilingEntry(K key) {
			return forward().floorEntry(key);
		}

		@Override
		public K ceilingKey(K key) {
			return forward().floorKey(key);
		}

		@Override
		public Entry<K, V> higherEntry(K key) {
			return forward().lowerEntry(key);
		}

		@Override
		public K higherKey(K key) {
			return forward().lowerKey(key);
		}

		@Override
		public Entry<K, V> firstEntry() {
			return forward().lastEntry();
		}

		@Override
		public Entry<K, V> lastEntry() {
			return forward().firstEntry();
		}

		@Override
		public Entry<K, V> pollFirstEntry() {
			return forward().pollLastEntry();
		}

		@Override
		public Entry<K, V> pollLastEntry() {
			return forward().pollFirstEntry();
		}

		@Override
		public NavigableMap<K, V> descendingMap() {
			return forward();
		}

		private transient Set<Entry<K, V>> entrySet;

		@Override
		public Set<Entry<K, V>> entrySet() {
			Set<Entry<K, V>> result = entrySet;
			return (result == null) ? entrySet = createEntrySet() : result;
		}

		abstract Iterator<Entry<K, V>> entryIterator();

		Set<Entry<K, V>> createEntrySet() {
			return new EntrySet<K, V>() {
				@Override
				Map<K, V> map() {
					return DescendingMap.this;
				}

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

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

		private transient NavigableSet<K> navigableKeySet;

		@Override
		public NavigableSet<K> navigableKeySet() {
			NavigableSet<K> result = navigableKeySet;
			return (result == null) ? navigableKeySet = new NavigableKeySet<K, V>(this) : result;
		}

		@Override
		public NavigableSet<K> descendingKeySet() {
			return forward().navigableKeySet();
		}

		@Override
		public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
			return forward().subMap(toKey, toInclusive, fromKey, fromInclusive).descendingMap();
		}

		@Override
		public NavigableMap<K, V> headMap(K toKey, boolean inclusive) {
			return forward().tailMap(toKey, inclusive).descendingMap();
		}

		@Override
		public NavigableMap<K, V> tailMap(K fromKey, boolean inclusive) {
			return forward().headMap(fromKey, inclusive).descendingMap();
		}

		@Override
		public SortedMap<K, V> subMap(K fromKey, K toKey) {
			return subMap(fromKey, true, toKey, false);
		}

		@Override
		public SortedMap<K, V> headMap(K toKey) {
			return headMap(toKey, false);
		}

		@Override
		public SortedMap<K, V> tailMap(K fromKey) {
			return tailMap(fromKey, true);
		}

		@Override
		public Collection<V> values() {
			return new Values<K, V>(this);
		}

		@Override
		public String toString() {
			return standardToString();
		}
	}
}