org.apache.commons.collections.map.IdentityMap Maven / Gradle / Ivy
/*
* 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 Map implementation that matches keys and values based
* on == not equals().
*
* This map will violate the detail of various Map and map view contracts.
* As a general rule, don't compare this map to other maps.
*
* Note that IdentityMap is not synchronized and is not thread-safe.
* 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 Commons Collections 3.0
* @version $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
*
* @author java util HashMap
* @author Stephen Colebourne
*/
public class IdentityMap
extends AbstractHashedMap 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 less than one
*/
public IdentityMap(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 less than one
* @throws IllegalArgumentException if the load factor is less than zero
*/
public IdentityMap(int initialCapacity, 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(Map 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
*/
protected int hash(Object key) {
return System.identityHashCode(key);
}
/**
* Compares two keys for equals.
* This implementation uses ==.
*
* @param key1 the first key to compare
* @param key2 the second key to compare
* @return true if equal by identity
*/
protected boolean isEqualKey(Object key1, Object key2) {
return (key1 == key2);
}
/**
* Compares two values for equals.
* This implementation uses ==.
*
* @param value1 the first value to compare
* @param value2 the second value to compare
* @return true if equal by identity
*/
protected boolean isEqualValue(Object value1, 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
*/
protected HashEntry createEntry(HashEntry next, int hashCode, Object key, Object value) {
return new IdentityEntry(next, hashCode, key, value);
}
//-----------------------------------------------------------------------
/**
* HashEntry
*/
protected static class IdentityEntry extends HashEntry {
protected IdentityEntry(HashEntry next, int hashCode, Object key, Object value) {
super(next, hashCode, key, value);
}
public boolean equals(Object obj) {
if (obj == this) {
return true;
}
if (obj instanceof Map.Entry == false) {
return false;
}
Map.Entry other = (Map.Entry) obj;
return
(getKey() == other.getKey()) &&
(getValue() == other.getValue());
}
public int hashCode() {
return System.identityHashCode(getKey()) ^
System.identityHashCode(getValue());
}
}
//-----------------------------------------------------------------------
/**
* Clones the map without cloning the keys or values.
*
* @return a shallow clone
*/
public Object clone() {
return super.clone();
}
/**
* Write the map out using a custom routine.
*/
private void writeObject(ObjectOutputStream out) throws IOException {
out.defaultWriteObject();
doWriteObject(out);
}
/**
* Read the map in using a custom routine.
*/
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
in.defaultReadObject();
doReadObject(in);
}
}