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