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;
020
021import java.util.Map;
022import java.util.Set;
023
024import javax.annotation.Nullable;
025
026/**
027 * A bimap (or "bidirectional map") is a map that preserves the uniqueness of
028 * its values as well as that of its keys. This constraint enables bimaps to
029 * support an "inverse view", which is another bimap containing the same entries
030 * as this bimap but with reversed keys and values.
031 *
032 * <p>See the Guava User Guide article on <a href=
033 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#bimap">
034 * {@code BiMap}</a>.
035 *
036 * @author Kevin Bourrillion
037 * @since 2.0
038 */
039@GwtCompatible
040public interface BiMap<K, V> extends Map<K, V> {
041  // Modification Operations
042
043  /**
044   * {@inheritDoc}
045   *
046   * @throws IllegalArgumentException if the given value is already bound to a
047   *     different key in this bimap. The bimap will remain unmodified in this
048   *     event. To avoid this exception, call {@link #forcePut} instead.
049   */
050  @Override
051  @Nullable
052  V put(@Nullable K key, @Nullable V value);
053
054  /**
055   * An alternate form of {@code put} that silently removes any existing entry
056   * with the value {@code value} before proceeding with the {@link #put}
057   * operation. If the bimap previously contained the provided key-value
058   * mapping, this method has no effect.
059   *
060   * <p>Note that a successful call to this method could cause the size of the
061   * bimap to increase by one, stay the same, or even decrease by one.
062   *
063   * <p><b>Warning:</b> If an existing entry with this value is removed, the key
064   * for that entry is discarded and not returned.
065   *
066   * @param key the key with which the specified value is to be associated
067   * @param value the value to be associated with the specified key
068   * @return the value which was previously associated with the key, which may
069   *     be {@code null}, or {@code null} if there was no previous entry
070   */
071  @Nullable
072  V forcePut(@Nullable K key, @Nullable V value);
073
074  // Bulk Operations
075
076  /**
077   * {@inheritDoc}
078   *
079   * <p><b>Warning:</b> the results of calling this method may vary depending on
080   * the iteration order of {@code map}.
081   *
082   * @throws IllegalArgumentException if an attempt to {@code put} any
083   *     entry fails. Note that some map entries may have been added to the
084   *     bimap before the exception was thrown.
085   */
086  @Override
087  void putAll(Map<? extends K, ? extends V> map);
088
089  // Views
090
091  /**
092   * {@inheritDoc}
093   *
094   * <p>Because a bimap has unique values, this method returns a {@link Set},
095   * instead of the {@link java.util.Collection} specified in the {@link Map}
096   * interface.
097   */
098  @Override
099  Set<V> values();
100
101  /**
102   * Returns the inverse view of this bimap, which maps each of this bimap's
103   * values to its associated key. The two bimaps are backed by the same data;
104   * any changes to one will appear in the other.
105   *
106   * <p><b>Note:</b>There is no guaranteed correspondence between the iteration
107   * order of a bimap and that of its inverse.
108   *
109   * @return the inverse view of this bimap
110   */
111  BiMap<V, K> inverse();
112}