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Google Collections Library is a suite of new collections and collection-related goodness for Java 5.0
There is a newer version: 1.0
/*
 * 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 static com.google.common.base.Preconditions.checkArgument;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.EnumMap;
import java.util.Map;

/**
 * A {@code BiMap} backed by two {@code EnumMap} instances. Null keys and values
 * are not permitted. An {@code EnumBiMap} and its inverse are both
 * serializable.
 *
 * @author Mike Bostock
 */
public final class EnumBiMap, V extends Enum>
    extends StandardBiMap {
  private transient Class keyType;
  private transient Class valueType;

  /**
   * Returns a new empty {@code EnumBiMap} using the specified key and value
   * types.
   *
   * @param keyType the key type
   * @param valueType the value type
   */
  public static , V extends Enum> EnumBiMap
      create(Class keyType, Class valueType) {
    return new EnumBiMap(keyType, valueType);
  }

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

  private EnumBiMap(Class keyType, Class valueType) {
    super(new EnumMap(keyType), new EnumMap(valueType));
    this.keyType = keyType;
    this.valueType = valueType;
  }

  static > Class inferKeyType(Map map) {
    if (map instanceof EnumBiMap) {
      return ((EnumBiMap) map).keyType();
    }
    if (map instanceof EnumHashBiMap) {
      return ((EnumHashBiMap) map).keyType();
    }
    checkArgument(!map.isEmpty());
    return map.keySet().iterator().next().getDeclaringClass();
  }

  private static > Class inferValueType(Map map) {
    if (map instanceof EnumBiMap) {
      return ((EnumBiMap) map).valueType;
    }
    checkArgument(!map.isEmpty());
    return map.values().iterator().next().getDeclaringClass();
  }

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

  /** Returns the associated value type. */
  public Class valueType() {
    return valueType;
  }

  /**
   * @serialData the key class, value 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);
    stream.writeObject(valueType);
    Serialization.writeMap(this, stream);
  }

  @SuppressWarnings("unchecked") // reading fields populated by writeObject
  private void readObject(ObjectInputStream stream)
      throws IOException, ClassNotFoundException {
    stream.defaultReadObject();
    keyType = (Class) stream.readObject();
    valueType = (Class) stream.readObject();
    setDelegates(new EnumMap(keyType), new EnumMap(valueType));
    Serialization.populateMap(this, stream);
  }

  private static final long serialVersionUID = 0;
}