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.jspecify.annotations.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 * <h3>Implementations</h3>
031 *
032 * <ul>
033 *   <li>{@link ImmutableBiMap}
034 *   <li>{@link HashBiMap}
035 *   <li>{@link EnumBiMap}
036 *   <li>{@link EnumHashBiMap}
037 * </ul>
038 *
039 * <p>See the Guava User Guide article on <a href=
040 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#bimap">{@code BiMap}</a>.
041 *
042 * @author Kevin Bourrillion
043 * @since 2.0
044 */
045@GwtCompatible
046public interface BiMap<K extends @Nullable Object, V extends @Nullable Object> extends Map<K, V> {
047  // Modification Operations
048
049  /**
050   * {@inheritDoc}
051   *
052   * @throws IllegalArgumentException if the given value is already bound to a different key in this
053   *     bimap. The bimap will remain unmodified in this event. To avoid this exception, call {@link
054   *     #forcePut} instead.
055   */
056  @CanIgnoreReturnValue
057  @Override
058  @Nullable V put(@ParametricNullness K key, @ParametricNullness V value);
059
060  /**
061   * An alternate form of {@code put} that silently removes any existing entry with the value {@code
062   * value} before proceeding with the {@link #put} operation. If the bimap previously contained the
063   * provided key-value mapping, this method has no effect.
064   *
065   * <p>Note that a successful call to this method could cause the size of the bimap to increase by
066   * one, stay the same, or even decrease by one.
067   *
068   * <p><b>Warning:</b> If an existing entry with this value is removed, the key for that entry is
069   * discarded and not returned.
070   *
071   * @param key the key with which the specified value is to be associated
072   * @param value the value to be associated with the specified key
073   * @return the value that was previously associated with the key, or {@code null} if there was no
074   *     previous entry. (If the bimap contains null values, then {@code forcePut}, like {@code
075   *     put}, returns {@code null} both if the key is absent and if it is present with a null
076   *     value.)
077   */
078  @CanIgnoreReturnValue
079  @Nullable V forcePut(@ParametricNullness K key, @ParametricNullness V value);
080
081  // Bulk Operations
082
083  /**
084   * {@inheritDoc}
085   *
086   * <p><b>Warning:</b> the results of calling this method may vary depending on the iteration order
087   * of {@code map}.
088   *
089   * @throws IllegalArgumentException if an attempt to {@code put} any entry fails. Note that some
090   *     map entries may have been added to the bimap before the exception was thrown.
091   */
092  @Override
093  void putAll(Map<? extends K, ? extends V> map);
094
095  // Views
096
097  /**
098   * {@inheritDoc}
099   *
100   * <p>Because a bimap has unique values, this method returns a {@link Set}, instead of the {@link
101   * java.util.Collection} specified in the {@link Map} interface.
102   */
103  @Override
104  Set<V> values();
105
106  /**
107   * Returns the inverse view of this bimap, which maps each of this bimap's values to its
108   * associated key. The two bimaps are backed by the same data; any changes to one will appear in
109   * the other.
110   *
111   * <p><b>Note:</b>There is no guaranteed correspondence between the iteration order of a bimap and
112   * that of its inverse.
113   *
114   * @return the inverse view of this bimap
115   */
116  BiMap<V, K> inverse();
117}