001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect;
018
019import com.google.common.annotations.GwtCompatible;
020import com.google.errorprone.annotations.CanIgnoreReturnValue;
021import java.util.Map;
022import java.util.Set;
023import org.checkerframework.checker.nullness.qual.Nullable;
024
025/**
026 * A bimap (or "bidirectional map") is a map that preserves the uniqueness of its values as well as
027 * that of its keys. This constraint enables bimaps to support an "inverse view", which is another
028 * bimap containing the same entries as this bimap but with reversed keys and values.
029 *
030 * <p>See the Guava User Guide article on <a href=
031 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#bimap"> {@code BiMap}</a>.
032 *
033 * @author Kevin Bourrillion
034 * @since 2.0
035 */
036@GwtCompatible
037public interface BiMap<K, V> extends Map<K, V> {
038  // Modification Operations
039
040  /**
041   * {@inheritDoc}
042   *
043   * @throws IllegalArgumentException if the given value is already bound to a different key in this
044   *     bimap. The bimap will remain unmodified in this event. To avoid this exception, call {@link
045   *     #forcePut} instead.
046   */
047  @CanIgnoreReturnValue
048  @Override
049  @Nullable
050  V put(@Nullable K key, @Nullable V value);
051
052  /**
053   * An alternate form of {@code put} that silently removes any existing entry with the value {@code
054   * value} before proceeding with the {@link #put} operation. If the bimap previously contained the
055   * provided key-value mapping, this method has no effect.
056   *
057   * <p>Note that a successful call to this method could cause the size of the bimap to increase by
058   * one, stay the same, or even decrease by one.
059   *
060   * <p><b>Warning:</b> If an existing entry with this value is removed, the key for that entry is
061   * discarded and not returned.
062   *
063   * @param key the key with which the specified value is to be associated
064   * @param value the value to be associated with the specified key
065   * @return the value which was previously associated with the key, which may be {@code null}, or
066   *     {@code null} if there was no previous entry
067   */
068  @CanIgnoreReturnValue
069  @Nullable
070  V forcePut(@Nullable K key, @Nullable V value);
071
072  // Bulk Operations
073
074  /**
075   * {@inheritDoc}
076   *
077   * <p><b>Warning:</b> the results of calling this method may vary depending on the iteration order
078   * of {@code map}.
079   *
080   * @throws IllegalArgumentException if an attempt to {@code put} any entry fails. Note that some
081   *     map entries may have been added to the bimap before the exception was thrown.
082   */
083  @Override
084  void putAll(Map<? extends K, ? extends V> map);
085
086  // Views
087
088  /**
089   * {@inheritDoc}
090   *
091   * <p>Because a bimap has unique values, this method returns a {@link Set}, instead of the {@link
092   * java.util.Collection} specified in the {@link Map} interface.
093   */
094  @Override
095  Set<V> values();
096
097  /**
098   * Returns the inverse view of this bimap, which maps each of this bimap's values to its
099   * associated key. The two bimaps are backed by the same data; any changes to one will appear in
100   * the other.
101   *
102   * <p><b>Note:</b>There is no guaranteed correspondence between the iteration order of a bimap and
103   * that of its inverse.
104   *
105   * @return the inverse view of this bimap
106   */
107  BiMap<V, K> inverse();
108}