android/guava/src/com/google/common/collect/BiMap.java

/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Map;
import java.util.Set;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;

/**
 * A bimap (or "bidirectional map") is a map that preserves the uniqueness of its values as well as
 * that of its keys. This constraint enables bimaps to support an "inverse view", which is another
 * bimap containing the same entries as this bimap but with reversed keys and values.
 *
 * <p>See the Guava User Guide article on <a href=
 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#bimap"> {@code BiMap}</a>.
 *
 * @author Kevin Bourrillion
 * @since 2.0
 */
@GwtCompatible
public interface BiMap<K, V> extends Map<K, V> {
  // Modification Operations

  /**
   * {@inheritDoc}
   *
   * @throws IllegalArgumentException if the given value is already bound to a different key in this
   *     bimap. The bimap will remain unmodified in this event. To avoid this exception, call {@link
   *     #forcePut} instead.
   */
  @CanIgnoreReturnValue
  @Override
  @NullableDecl
  V put(@NullableDecl K key, @NullableDecl V value);

  /**
   * An alternate form of {@code put} that silently removes any existing entry with the value {@code
   * value} before proceeding with the {@link #put} operation. If the bimap previously contained the
   * provided key-value mapping, this method has no effect.
   *
   * <p>Note that a successful call to this method could cause the size of the bimap to increase by
   * one, stay the same, or even decrease by one.
   *
   * <p><b>Warning:</b> If an existing entry with this value is removed, the key for that entry is
   * discarded and not returned.
   *
   * @param key the key with which the specified value is to be associated
   * @param value the value to be associated with the specified key
   * @return the value which was previously associated with the key, which may be {@code null}, or
   *     {@code null} if there was no previous entry
   */
  @CanIgnoreReturnValue
  @NullableDecl
  V forcePut(@NullableDecl K key, @NullableDecl V value);

  // Bulk Operations

  /**
   * {@inheritDoc}
   *
   * <p><b>Warning:</b> the results of calling this method may vary depending on the iteration order
   * of {@code map}.
   *
   * @throws IllegalArgumentException if an attempt to {@code put} any entry fails. Note that some
   *     map entries may have been added to the bimap before the exception was thrown.
   */
  @Override
  void putAll(Map<? extends K, ? extends V> map);

  // Views

  /**
   * {@inheritDoc}
   *
   * <p>Because a bimap has unique values, this method returns a {@link Set}, instead of the {@link
   * java.util.Collection} specified in the {@link Map} interface.
   */
  @Override
  Set<V> values();

  /**
   * Returns the inverse view of this bimap, which maps each of this bimap's values to its
   * associated key. The two bimaps are backed by the same data; any changes to one will appear in
   * the other.
   *
   * <p><b>Note:</b>There is no guaranteed correspondence between the iteration order of a bimap and
   * that of its inverse.
   *
   * @return the inverse view of this bimap
   */
  BiMap<V, K> inverse();
}