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Google Collections Library is a suite of new collections and collection-related goodness for Java 5.0
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/*
 * Copyright (C) 2007 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 java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.Map;

import javax.annotation.Nullable;

/**
 * A {@code BiMap} backed by an {@code EnumMap} instance for keys-to-values, and
 * a {@code HashMap} instance for values-to-keys. Null keys are not permitted,
 * but null values are. An {@code EnumHashBiMap} and its inverse are both
 * serializable.
 *
 * @author Mike Bostock
 */
public final class EnumHashBiMap, V>
    extends AbstractBiMap {
  private transient Class keyType;

  /**
   * Returns a new, empty {@code EnumHashBiMap} using the specified key type.
   *
   * @param keyType the key type
   */
  public static , V> EnumHashBiMap
      create(Class keyType) {
    return new EnumHashBiMap(keyType);
  }

  /**
   * Constructs a new bimap with the same mappings as the specified map. If the
   * specified map is an {@code EnumHashBiMap} or an {@link EnumBiMap}, the new
   * bimap has the same key type as the input bimap. Otherwise, the specified
   * map must contain at least one mapping, in order to determine the key type.
   *
   * @param map the map whose mappings are to be placed in this map
   * @throws IllegalArgumentException if map is not an {@code EnumBiMap} or an
   *     {@code EnumHashBiMap} instance and contains no mappings
   */
  public static , V> EnumHashBiMap
      create(Map map) {
    EnumHashBiMap bimap = create(EnumBiMap.inferKeyType(map));
    bimap.putAll(map);
    return bimap;
  }

  private EnumHashBiMap(Class keyType) {
    super(new EnumMap(keyType), Maps.newHashMapWithExpectedSize(
        keyType.getEnumConstants().length));
    this.keyType = keyType;
  }

  // Overriding these two methods to show that values may be null (but not keys)

  @Override public V put(K key, @Nullable V value) {
    return super.put(key, value);
  }

  @Override public V forcePut(K key, @Nullable V value) {
    return super.forcePut(key, value);
  }

  /** Returns the associated key type. */
  public Class keyType() {
    return keyType;
  }

  /**
   * @serialData the key class, number of entries, first key, first value,
   *     second key, second value, and so on.
   */
  private void writeObject(ObjectOutputStream stream) throws IOException {
    stream.defaultWriteObject();
    stream.writeObject(keyType);
    Serialization.writeMap(this, stream);
  }

  @SuppressWarnings("unchecked") // reading field populated by writeObject
  private void readObject(ObjectInputStream stream)
      throws IOException, ClassNotFoundException {
    stream.defaultReadObject();
    keyType = (Class) stream.readObject();
    setDelegates(new EnumMap(keyType),
        new HashMap(keyType.getEnumConstants().length * 3 / 2));
    Serialization.populateMap(this, stream);
  }

  private static final long serialVersionUID = 0;
}