package org.apache.commons.collections4.map;

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

/** 
 * 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.
 * <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.
 * 
 * @version $Id$
 * @since 3.0
 */
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(AbstractHashedMap.DEFAULT_CAPACITY, AbstractHashedMap.DEFAULT_LOAD_FACTOR, AbstractHashedMap.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 java.lang.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 AbstractHashedMap.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 AbstractHashedMap.HashEntry<K, V> {
        protected IdentityEntry(final AbstractHashedMap.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)) {
                return false;
            } 
            final Map.Entry<?, ?> other = ((Map.Entry<?, ?>)(obj));
            return ((getKey()) == (other.getKey())) && ((getValue()) == (other.getValue()));
        }

        @Override
        public int hashCode() {
            return (java.lang.System.identityHashCode(getKey())) ^ (java.lang.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);
    }
}