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Commons Collections example source code file (IdentityMap.java)

This example Commons Collections source code file (IdentityMap.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

abstracthashedmap, classnotfoundexception, cloneable, default_load_factor, hashentry, identityentry, identityentry, identitymap, identitymap, io, ioexception, ioexception, object, object, serializable, util

The Commons Collections IdentityMap.java source code

/*
 *  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 implementation that matches keys and values based
 * on <code>== not equals().
 * <p>
 * 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.
 * <p>
 * <strong>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 13:33:15 +0100 (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 <code>==.
     * 
     * @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 <code>==.
     * 
     * @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);
    }
    
}

Other Commons Collections examples (source code examples)

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