src/com/google/common/collect/ImmutableBiMap.java

/*
 * Copyright (C) 2008 Google Inc.
 *
 * 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 java.util.Map;

import javax.annotation.Nullable;

/**
 * An immutable {@link BiMap} with reliable user-specified iteration order. Does
 * not permit null keys or values. An {@code ImmutableBiMap} and its inverse
 * have the same iteration ordering.
 *
 * <p>An instance of {@code ImmutableBiMap} contains its own data and will
 * <i>never</i> change. {@code ImmutableBiMap} is convenient for
 * {@code public static final} maps ("constant maps") and also lets you easily
 * make a "defensive copy" of a bimap provided to your class by a caller.
 *
 * <p><b>Note</b>: Although this class is not final, it cannot be subclassed as
 * it has no public or protected constructors. Thus, instances of this class are
 * guaranteed to be immutable.
 *
 * @author Jared Levy
 */
@GwtCompatible(serializable = true)
public abstract class ImmutableBiMap<K, V> extends ImmutableMap<K, V>
    implements BiMap<K, V> {

  private static final ImmutableBiMap<Object, Object> EMPTY_IMMUTABLE_BIMAP
      = new EmptyBiMap();

  /**
   * Returns the empty bimap.
   */
  // Casting to any type is safe because the set will never hold any elements.
  @SuppressWarnings("unchecked")
  public static <K, V> ImmutableBiMap<K, V> of() {
    return (ImmutableBiMap<K, V>) EMPTY_IMMUTABLE_BIMAP;
  }

  /**
   * Returns an immutable bimap containing a single entry.
   */
  public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1) {
    return new RegularImmutableBiMap<K, V>(ImmutableMap.of(k1, v1));
  }

  /**
   * Returns an immutable map containing the given entries, in order.
   *
   * @throws IllegalArgumentException if duplicate keys or values are added
   */
  public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2) {
    return new RegularImmutableBiMap<K, V>(ImmutableMap.of(k1, v1, k2, v2));
  }

  /**
   * Returns an immutable map containing the given entries, in order.
   *
   * @throws IllegalArgumentException if duplicate keys or values are added
   */
  public static <K, V> ImmutableBiMap<K, V> of(
      K k1, V v1, K k2, V v2, K k3, V v3) {
    return new RegularImmutableBiMap<K, V>(ImmutableMap.of(
        k1, v1, k2, v2, k3, v3));
  }

  /**
   * Returns an immutable map containing the given entries, in order.
   *
   * @throws IllegalArgumentException if duplicate keys or values are added
   */
  public static <K, V> ImmutableBiMap<K, V> of(
      K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
    return new RegularImmutableBiMap<K, V>(ImmutableMap.of(
        k1, v1, k2, v2, k3, v3, k4, v4));
  }

  /**
   * Returns an immutable map containing the given entries, in order.
   *
   * @throws IllegalArgumentException if duplicate keys or values are added
   */
  public static <K, V> ImmutableBiMap<K, V> of(
      K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
    return new RegularImmutableBiMap<K, V>(ImmutableMap.of(
        k1, v1, k2, v2, k3, v3, k4, v4, k5, v5));
  }

  // looking for of() with > 5 entries? Use the builder instead.

  /**
   * Returns a new builder. The generated builder is equivalent to the builder
   * created by the {@link Builder} constructor.
   */
  public static <K, V> Builder<K, V> builder() {
    return new Builder<K, V>();
  }

  /**
   * A builder for creating immutable bimap instances, especially {@code public
   * static final} bimaps ("constant bimaps"). Example: <pre>   {@code
   *
   *   static final ImmutableBiMap<String, Integer> WORD_TO_INT =
   *       new ImmutableBiMap.Builder<String, Integer>()
   *           .put("one", 1)
   *           .put("two", 2)
   *           .put("three", 3)
   *           .build();}</pre>
   *
   * For <i>small</i> immutable bimaps, the {@code ImmutableBiMap.of()} methods
   * are even more convenient.
   *
   * <p>Builder instances can be reused - it is safe to call {@link #build}
   * multiple times to build multiple bimaps in series. Each bimap is a superset
   * of the bimaps created before it.
   */
  public static final class Builder<K, V> extends ImmutableMap.Builder<K, V> {

    /**
     * Creates a new builder. The returned builder is equivalent to the builder
     * generated by {@link ImmutableBiMap#builder}.
     */
    public Builder() {}

    /**
     * Associates {@code key} with {@code value} in the built bimap. Duplicate
     * keys or values are not allowed, and will cause {@link #build} to fail.
     */
    @Override public Builder<K, V> put(K key, V value) {
      super.put(key, value);
      return this;
    }

    /**
     * Associates all of the given map's keys and values in the built bimap.
     * Duplicate keys or values are not allowed, and will cause {@link #build}
     * to fail.
     *
     * @throws NullPointerException if any key or value in {@code map} is null
     */
    @Override public Builder<K, V> putAll(Map<? extends K, ? extends V> map) {
      super.putAll(map);
      return this;
    }

    /**
     * Returns a newly-created immutable bimap.
     *
     * @throws IllegalArgumentException if duplicate keys or values were added
     */
    @Override public ImmutableBiMap<K, V> build() {
      ImmutableMap<K, V> map = super.build();
      if (map.isEmpty()) {
        return of();
      }
      return new RegularImmutableBiMap<K, V>(super.build());
    }
  }

  /**
   * Returns an immutable bimap containing the same entries as {@code map}. If
   * {@code map} somehow contains entries with duplicate keys (for example, if
   * it is a {@code SortedMap} whose comparator is not <i>consistent with
   * equals</i>), the results of this method are undefined.
   *
   * <p><b>Note:</b> If {@code map} is an {@code ImmutableBiMap}, the given map
   * itself will be returned.
   *
   * @throws IllegalArgumentException if two keys have the same value
   * @throws NullPointerException if any key or value in {@code map} is null
   */
  public static <K, V> ImmutableBiMap<K, V> copyOf(
      Map<? extends K, ? extends V> map) {
    if (map instanceof ImmutableBiMap) {
      @SuppressWarnings("unchecked") // safe since map is not writable
      ImmutableBiMap<K, V> bimap = (ImmutableBiMap<K, V>) map;
      return bimap;
    }

    if (map.isEmpty()) {
      return of();
    }

    ImmutableMap<K, V> immutableMap = ImmutableMap.copyOf(map);
    return new RegularImmutableBiMap<K, V>(immutableMap);
  }

  ImmutableBiMap() {}

  abstract ImmutableMap<K, V> delegate();

  /**
   * {@inheritDoc}
   *
   * <p>The inverse of an {@code ImmutableBiMap} is another
   * {@code ImmutableBiMap}.
   */
  public abstract ImmutableBiMap<V, K> inverse();

  @Override public boolean containsKey(@Nullable Object key) {
    return delegate().containsKey(key);
  }

  @Override public boolean containsValue(@Nullable Object value) {
    return inverse().containsKey(value);
  }

  @Override public ImmutableSet<Entry<K, V>> entrySet() {
    return delegate().entrySet();
  }

  @Override public V get(@Nullable Object key) {
    return delegate().get(key);
  }

  @Override public ImmutableSet<K> keySet() {
    return delegate().keySet();
  }

  /**
   * Returns an immutable set of the values in this map. The values are in the
   * same order as the parameters used to build this map.
   */
  @Override public ImmutableSet<V> values() {
    return inverse().keySet();
  }

  /**
   * Guaranteed to throw an exception and leave the bimap unmodified.
   *
   * @throws UnsupportedOperationException always
   */
  public V forcePut(K key, V value) {
    throw new UnsupportedOperationException();
  }

  @Override public boolean isEmpty() {
    return delegate().isEmpty();
  }

  public int size() {
    return delegate().size();
  }

  @Override public boolean equals(@Nullable Object object) {
    return object == this || delegate().equals(object);
  }

  @Override public int hashCode() {
    return delegate().hashCode();
  }

  @Override public String toString() {
    return delegate().toString();
  }

  /** Bimap with no mappings. */
  @SuppressWarnings("serial") // uses writeReplace(), not default serialization
  static class EmptyBiMap extends ImmutableBiMap<Object, Object> {
    @Override ImmutableMap<Object, Object> delegate() {
      return ImmutableMap.of();
    }
    @Override public ImmutableBiMap<Object, Object> inverse() {
      return this;
    }
    Object readResolve() {
      return EMPTY_IMMUTABLE_BIMAP; // preserve singleton property
    }
  }

  /**
   * Serialized type for all ImmutableBiMap instances. It captures the logical
   * contents and they are reconstructed using public factory methods. This
   * ensures that the implementation types remain as implementation details.
   *
   * Since the bimap is immutable, ImmutableBiMap doesn't require special logic
   * for keeping the bimap and its inverse in sync during serialization, the way
   * AbstractBiMap does.
   */
  private static class SerializedForm extends ImmutableMap.SerializedForm {
    SerializedForm(ImmutableBiMap<?, ?> bimap) {
      super(bimap);
    }
    @Override Object readResolve() {
      Builder<Object, Object> builder = new Builder<Object, Object>();
      return createMap(builder);
    }
    private static final long serialVersionUID = 0;
  }

  @Override Object writeReplace() {
    return new SerializedForm(this);
  }
}