/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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 org.apache.commons.collections4.map;
  
  import java.io.IOException;
  import java.io.ObjectInputStream;
  import java.io.ObjectOutputStream;
  import java.io.Serializable;
  import java.util.Map;
  
  /**
   * A {@code Map} implementation that matches keys and values based
   * on {@code ==} not {@code equals()}.
   * <p>
   * <strong>This map will violate the detail of various Map and map view contracts.</strong>
   * As a general rule, don't compare this map to other maps. In particular, you can't
   * use decorators like {@link ListOrderedMap} on it, which silently assume that these
   * contracts are fulfilled.
   * <p>
   * <strong>Note that IdentityMap is not synchronized and is not thread-safe.</strong>
   * If you wish to use this map from multiple threads concurrently, you must use
   * appropriate synchronization. The simplest approach is to wrap this map
   * using {@link java.util.Collections#synchronizedMap(Map)}. This class may throw
   * exceptions when accessed by concurrent threads without synchronization.
   * <p>
   * From 4.0, this class is replaced by java.util.IdentityHashMap but kept as a
   * test-class because it is still used by the ReferenceIdentityMapTest.
   *
   * @param <K> the type of the keys in this map
   * @param <V> the type of the values in this map
   */
  public class IdentityMap<K, V>
          extends AbstractHashedMap<K, V> implements Serializable, Cloneable {
  
      /**
       * HashEntry
       */
      protected static class IdentityEntry<K, V> extends HashEntry<K, V> {
  
          protected IdentityEntry(final HashEntry<K, V> next, final int hashCode, final K key, final V value) {
              super(next, hashCode, key, value);
          }
  
          @Override
          public boolean equals(final Object obj) {
              if (obj == this) {
                  return true;
              }
              if (!(obj instanceof Entry)) {
                  return false;
              }
              final Map.Entry<?, ?> other = (Map.Entry<?, ?>) obj;
              return
                  getKey() == other.getKey() &&
                  getValue() == other.getValue();
          }
  
          @Override
          public int hashCode() {
              return System.identityHashCode(getKey()) ^
                     System.identityHashCode(getValue());
          }
      }
  
      /** Serialisation version */
      private static final long serialVersionUID = 2028493495224302329L;
  
      /**
       * Constructs a new empty map with default size and load factor.
       */
      public IdentityMap() {
          super(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_THRESHOLD);
      }
  
      /**
       * Constructs a new, empty map with the specified initial capacity.
       *
       * @param initialCapacity  the initial capacity
       * @throws IllegalArgumentException if the initial capacity is negative
       */
      public IdentityMap(final int initialCapacity) {
          super(initialCapacity);
      }
  
      /**
      * Constructs a new, empty map with the specified initial capacity and
      * load factor.
      *
      * @param initialCapacity  the initial capacity
      * @param loadFactor  the load factor
      * @throws IllegalArgumentException if the initial capacity is negative
      * @throws IllegalArgumentException if the load factor is less than zero
      */
     public IdentityMap(final int initialCapacity, final float loadFactor) {
         super(initialCapacity, loadFactor);
     }
 
     /**
      * Constructor copying elements from another map.
      *
      * @param map  the map to copy
      * @throws NullPointerException if the map is null
      */
     public IdentityMap(final Map<K, V> map) {
         super(map);
     }
 
     /**
      * Clones the map without cloning the keys or values.
      *
      * @return a shallow clone
      */
     @Override
     public IdentityMap<K, V> clone() {
         return (IdentityMap<K, V>) super.clone();
     }
 
     /**
      * Creates an entry to store the data.
      * This implementation creates an IdentityEntry instance.
      *
      * @param next  the next entry in sequence
      * @param hashCode  the hash code to use
      * @param key  the key to store
      * @param value  the value to store
      * @return the newly created entry
      */
     @Override
     protected IdentityEntry<K, V> createEntry(final HashEntry<K, V> next, final int hashCode,
                                               final K key, final V value) {
         return new IdentityEntry<>(next, hashCode, key, value);
     }
 
     /**
      * Gets the hash code for the key specified.
      * This implementation uses the identity hash code.
      *
      * @param key  the key to get a hash code for
      * @return the hash code
      */
     @Override
     protected int hash(final Object key) {
         return System.identityHashCode(key);
     }
 
     /**
      * Compares two keys for equals.
      * This implementation uses {@code ==}.
      *
      * @param key1  the first key to compare
      * @param key2  the second key to compare
      * @return true if equal by identity
      */
     @Override
     protected boolean isEqualKey(final Object key1, final Object key2) {
         return key1 == key2;
     }
 
     /**
      * Compares two values for equals.
      * This implementation uses {@code ==}.
      *
      * @param value1  the first value to compare
      * @param value2  the second value to compare
      * @return true if equal by identity
      */
     @Override
     protected boolean isEqualValue(final Object value1, final Object value2) {
         return value1 == value2;
     }
 
     /**
      * Read the map in using a custom routine.
      */
     private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
         in.defaultReadObject();
         doReadObject(in);
     }
 
     /**
      * Write the map out using a custom routine.
      */
     private void writeObject(final ObjectOutputStream out) throws IOException {
         out.defaultWriteObject();
         doWriteObject(out);
     }
 
 }