/*
    * 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.collections.map;
  
  import java.io.IOException;
  import java.io.ObjectInputStream;
  import java.io.ObjectOutputStream;
  import java.io.Serializable;
  import java.util.Map;
  
  /**
   * A <code>Map</code> implementation that matches keys and values based
   * on <code>==</code> not <code>equals()</code>.
   * <p>
   * <strong>This map will violate the detail of various Map and map view contracts.</note>
   * 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.
   *
   * @since 3.0
   * @version $Id: IdentityMap.java 1435824 2013-01-20 11:41:17Z tn $
   */
  public class IdentityMap<K, V>
          extends AbstractHashedMap<K, V> implements Serializable, Cloneable {
  
      /** 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);
      }
  
      //-----------------------------------------------------------------------
      /**
       * 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>==</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>==</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;
     }
 
     /**
      * 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<K, V>(next, hashCode, key, value);
     }
 
     //-----------------------------------------------------------------------
     /**
      * 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 Map.Entry == false) {
                 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());
         }
     }
 
     //-----------------------------------------------------------------------
     /**
      * 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();
     }
 
     /**
      * Write the map out using a custom routine.
      */
     private void writeObject(final ObjectOutputStream out) throws IOException {
         out.defaultWriteObject();
         doWriteObject(out);
     }
 
     /**
      * Read the map in using a custom routine.
      */
     private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
         in.defaultReadObject();
         doReadObject(in);
     }
 
 }