com.google.common.collect.Maps.java Source code

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/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import 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 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;
import com.google.j2objc.annotations.Weak;
import com.google.j2objc.annotations.WeakOuter;

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 java.util.concurrent.ConcurrentMap;

import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;

/**
 * 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=
 * "https://github.com/google/guava/wiki/CollectionUtilitiesExplained#maps">
 * {@code Maps}</a>.
 *
 * @author Kevin Bourrillion
 * @author Mike Bostock
 * @author Isaac Shum
 * @author Louis Wasserman
 * @since 2.0
 */
@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());
    }

    /**
     * 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 1.7. It also can't be guaranteed that the method isn't
     * inadvertently <i>oversizing</i> the returned map.
     *
     * @param expectedSize the number of entries you expect to add to the
     *        returned map
     * @return a new, empty {@code HashMap} with enough capacity to hold {@code
     *         expectedSize} entries 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) {
            // This is the calculation used in JDK8 to resize when a putAll
            // happens; it seems to be the most conservative calculation we
            // can make.  0.75 is the default load factor.
            return (int) ((float) expectedSize / 0.75F + 1.0F);
        }
        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 {@code LinkedHashMap} 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 1.7. It also can't be guaranteed
     * that the method isn't inadvertently <i>oversizing</i> the returned map.
     *
     * @param expectedSize the number of entries you expect to add to the
     *        returned map
     * @return a new, empty {@code LinkedHashMap} with enough capacity to hold
     *         {@code expectedSize} entries without resizing
     * @throws IllegalArgumentException if {@code expectedSize} is negative
     * @since 19.0
     */
    public static <K, V> LinkedHashMap<K, V> newLinkedHashMapWithExpectedSize(int expectedSize) {
        return new LinkedHashMap<K, V>(capacity(expectedSize));
    }

    /**
     * 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);
    }

    /**
     * Returns a general-purpose instance of {@code ConcurrentMap}, which supports
     * all optional operations of the ConcurrentMap interface. It does not permit
     * null keys or values. It is serializable.
     *
     * <p>This is currently accomplished by calling {@link MapMaker#makeMap()}.
     *
     * <p>It is preferable to use {@code MapMaker} directly (rather than through
     * this method), as it presents numerous useful configuration options,
     * such as the concurrency level, load factor, key/value reference types,
     * and value computation.
     *
     * @return a new, empty {@code ConcurrentMap}
     * @since 3.0
     */
    public static <K, V> ConcurrentMap<K, V> newConcurrentMap() {
        return new MapMaker().<K, V>makeMap();
    }

    /**
     * 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 = newLinkedHashMap();
        Map<K, V> onlyOnRight = new LinkedHashMap<K, V>(right); // will whittle it down
        Map<K, V> onBoth = newLinkedHashMap();
        Map<K, MapDifference.ValueDifference<V>> differences = newLinkedHashMap();
        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
     */
    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
     */
    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
     */
    @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 ViewCachingAbstractMap<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() {
            @WeakOuter
            class EntrySetImpl extends EntrySet<K, V> {
                @Override
                Map<K, V> map() {
                    return AsMapView.this;
                }

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

    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>When there are multiple instances of a key in {@code keys}, it is
     * unspecified whether {@code valueFunction} will be applied to more than one
     * instance of that key and, if it is, which result will be mapped to that
     * key in the returned map.
     *
     * <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
     */
    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}.
     *
     * <p>When there are multiple instances of a key in {@code keys}, it is
     * unspecified whether {@code valueFunction} will be applied to more than one
     * instance of that key and, if it is, which result will be mapped to that
     * key in the returned map.
     *
     * @throws NullPointerException if any element of {@code keys} is
     *     {@code null}, or if {@code valueFunction} produces {@code null}
     *     for any key
     * @since 14.0
     */
    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 a map with the given {@code values}, indexed by keys derived from
     * those values. In other words, each input value produces an entry in the map
     * whose key is the result of applying {@code keyFunction} to that value.
     * These entries appear in the same order as the input values. Example usage:
     * <pre>   {@code
     *
     *   Color red = new Color("red", 255, 0, 0);
     *   ...
     *   ImmutableSet<Color> allColors = ImmutableSet.of(red, green, blue);
     *
     *   Map<String, Color> colorForName =
     *       uniqueIndex(allColors, toStringFunction());
     *   assertThat(colorForName).containsEntry("red", red);}</pre>
     *
     * <p>If your index may associate multiple values with each key, use {@link
     * Multimaps#index(Iterable, Function) Multimaps.index}.
     *
     * @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) {
        // TODO(lowasser): consider presizing the builder if values is a Collection
        return uniqueIndex(values.iterator(), keyFunction);
    }

    /**
     * Returns a map with the given {@code values}, indexed by keys derived from
     * those values. In other words, each input value produces an entry in the map
     * whose key is the result of applying {@code keyFunction} to that value.
     * These entries appear in the same order as the input values. Example usage:
     * <pre>   {@code
     *
     *   Color red = new Color("red", 255, 0, 0);
     *   ...
     *   Iterator<Color> allColors = ImmutableSet.of(red, green, blue).iterator();
     *
     *   Map<String, Color> colorForName =
     *       uniqueIndex(allColors, toStringFunction());
     *   assertThat(colorForName).containsEntry("red", red);}</pre>
     *
     * <p>If your index may associate multiple values with each key, use {@link
     * Multimaps#index(Iterator, Function) Multimaps.index}.
     *
     * @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);
        }
        try {
            return builder.build();
        } catch (IllegalArgumentException duplicateKeys) {
            throw new IllegalArgumentException(
                    duplicateKeys.getMessage() + ". To index multiple values under a key, use Multimaps.index.");
        }
    }

    /**
     * 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();
            }
        };
    }

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

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

    /** @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() {
            return unmodifiableEntryIterator(entries.iterator());
        }

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

        @Override
        public Collection<V2> values() {
            return new Values<K, V2>(this);
        }
    }

    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.
     */
    @CheckReturnValue
    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
     */
    @CheckReturnValue
    public static <K, V> SortedMap<K, V> filterKeys(SortedMap<K, V> unfiltered,
            final Predicate<? super K> keyPredicate) {
        // TODO(lowasser): 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")
    @CheckReturnValue
    public static <K, V> NavigableMap<K, V> filterKeys(NavigableMap<K, V> unfiltered,
            final Predicate<? super K> keyPredicate) {
        // TODO(lowasser): 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
     */
    @CheckReturnValue
    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.
     */
    @CheckReturnValue
    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
     */
    @CheckReturnValue
    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")
    @CheckReturnValue
    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
     */
    @CheckReturnValue
    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}.
     */
    @CheckReturnValue
    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
     */
    @CheckReturnValue
    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")
    @CheckReturnValue
    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
     */
    @CheckReturnValue
    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 ViewCachingAbstractMap<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();
        }

        @WeakOuter
        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();
        }

        @WeakOuter
        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();
        }

        @WeakOuter
        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
        public boolean isEmpty() {
            return !Iterables.any(unfiltered.entrySet(), entryPredicate);
        }

        @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>   {@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>   {@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 makes it easy to cache customized keySet, values,
     * and entrySet views.
     */
    @GwtCompatible
    abstract static class ViewCachingAbstractMap<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);
        }
    }

    abstract static class IteratorBasedAbstractMap<K, V> extends AbstractMap<K, V> {
        @Override
        public abstract int size();

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

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

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

        @Override
        public void clear() {
            Iterators.clear(entryIterator());
        }
    }

    /**
     * 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> {
        @Weak
        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> {
        @Weak
        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() {
            @WeakOuter
            class EntrySetImpl extends EntrySet<K, V> {
                @Override
                Map<K, V> map() {
                    return DescendingMap.this;
                }

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

        @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();
        }
    }

    /**
     * Returns a map from the ith element of list to i.
     */
    static <E> ImmutableMap<E, Integer> indexMap(Collection<E> list) {
        ImmutableMap.Builder<E, Integer> builder = new ImmutableMap.Builder<E, Integer>(list.size());
        int i = 0;
        for (E e : list) {
            builder.put(e, i++);
        }
        return builder.build();
    }
}