IdentityMap.java
/*
* 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
*
* https://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.
*
* @param <K> the key type.
* @param <V> the value type.
*/
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());
}
}
/** Serialization 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;
}
/**
* Deserializes an instance from an ObjectInputStream.
*
* @param in The source ObjectInputStream.
* @throws IOException Any of the usual Input/Output related exceptions.
* @throws ClassNotFoundException A class of a serialized object cannot be found.
*/
private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
in.defaultReadObject();
doReadObject(in);
}
/**
* Serializes this object to an ObjectOutputStream.
*
* @param out the target ObjectOutputStream.
* @throws IOException thrown when an I/O errors occur writing to the target stream.
*/
private void writeObject(final ObjectOutputStream out) throws IOException {
out.defaultWriteObject();
doWriteObject(out);
}
}