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 javax.annotation.CheckForNull;
024import org.checkerframework.checker.nullness.qual.Nullable;
025
026/**
027 * A bimap (or "bidirectional map") is a map that preserves the uniqueness of its values as well as
028 * that of its keys. This constraint enables bimaps to support an "inverse view", which is another
029 * bimap containing the same entries as this bimap but with reversed keys and values.
030 *
031 * <h3>Implementations</h3>
032 *
033 * <ul>
034 *   <li>{@link ImmutableBiMap}
035 *   <li>{@link HashBiMap}
036 *   <li>{@link EnumBiMap}
037 *   <li>{@link EnumHashBiMap}
038 * </ul>
039 *
040 * <p>See the Guava User Guide article on <a href=
041 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#bimap">{@code BiMap}</a>.
042 *
043 * @author Kevin Bourrillion
044 * @since 2.0
045 */
046@GwtCompatible
047@ElementTypesAreNonnullByDefault
048public interface BiMap<K extends @Nullable Object, V extends @Nullable Object> extends Map<K, V> {
049  // Modification Operations
050
051  /**
052   * {@inheritDoc}
053   *
054   * @throws IllegalArgumentException if the given value is already bound to a different key in this
055   *     bimap. The bimap will remain unmodified in this event. To avoid this exception, call {@link
056   *     #forcePut} instead.
057   */
058  @CanIgnoreReturnValue
059  @Override
060  @CheckForNull
061  V put(@ParametricNullness K key, @ParametricNullness V value);
062
063  /**
064   * An alternate form of {@code put} that silently removes any existing entry with the value {@code
065   * value} before proceeding with the {@link #put} operation. If the bimap previously contained the
066   * provided key-value mapping, this method has no effect.
067   *
068   * <p>Note that a successful call to this method could cause the size of the bimap to increase by
069   * one, stay the same, or even decrease by one.
070   *
071   * <p><b>Warning:</b> If an existing entry with this value is removed, the key for that entry is
072   * discarded and not returned.
073   *
074   * @param key the key with which the specified value is to be associated
075   * @param value the value to be associated with the specified key
076   * @return the value that was previously associated with the key, or {@code null} if there was no
077   *     previous entry. (If the bimap contains null values, then {@code forcePut}, like {@code
078   *     put}, returns {@code null} both if the key is absent and if it is present with a null
079   *     value.)
080   */
081  @CanIgnoreReturnValue
082  @CheckForNull
083  V forcePut(@ParametricNullness K key, @ParametricNullness V value);
084
085  // Bulk Operations
086
087  /**
088   * {@inheritDoc}
089   *
090   * <p><b>Warning:</b> the results of calling this method may vary depending on the iteration order
091   * of {@code map}.
092   *
093   * @throws IllegalArgumentException if an attempt to {@code put} any entry fails. Note that some
094   *     map entries may have been added to the bimap before the exception was thrown.
095   */
096  @Override
097  void putAll(Map<? extends K, ? extends V> map);
098
099  // Views
100
101  /**
102   * {@inheritDoc}
103   *
104   * <p>Because a bimap has unique values, this method returns a {@link Set}, instead of the {@link
105   * java.util.Collection} specified in the {@link Map} interface.
106   */
107  @Override
108  Set<V> values();
109
110  /**
111   * Returns the inverse view of this bimap, which maps each of this bimap's values to its
112   * associated key. The two bimaps are backed by the same data; any changes to one will appear in
113   * the other.
114   *
115   * <p><b>Note:</b>There is no guaranteed correspondence between the iteration order of a bimap and
116   * that of its inverse.
117   *
118   * @return the inverse view of this bimap
119   */
120  BiMap<V, K> inverse();
121}