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/*
 * 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.collections4.keyvalue;

import java.io.Serializable;
import java.util.Arrays;

/**
 * A MultiKey allows multiple map keys to be merged together.
 * 

* The purpose of this class is to avoid the need to write code to handle * maps of maps. An example might be the need to look up a file name by * key and locale. The typical solution might be nested maps. This class * can be used instead by creating an instance passing in the key and locale. *

* Example usage: *

 * // populate map with data mapping key+locale to localizedText
 * Map map = new HashMap();
 * MultiKey multiKey = new MultiKey(key, locale);
 * map.put(multiKey, localizedText);
 *
 * // later retrieve the localized text
 * MultiKey multiKey = new MultiKey(key, locale);
 * String localizedText = (String) map.get(multiKey);
 * 
* * @since 3.0 * @version $Id: MultiKey.java 1705620 2015-09-28 08:53:44Z tn $ */ public class MultiKey implements Serializable { // This class could implement List, but that would confuse it's purpose /** Serialisation version */ private static final long serialVersionUID = 4465448607415788805L; /** The individual keys */ private final K[] keys; /** The cached hashCode */ private transient int hashCode; /** * Constructor taking two keys. *

* The keys should be immutable * If they are not then they must not be changed after adding to the MultiKey. * * @param key1 the first key * @param key2 the second key */ @SuppressWarnings("unchecked") public MultiKey(final K key1, final K key2) { this((K[]) new Object[] { key1, key2 }, false); } /** * Constructor taking three keys. *

* The keys should be immutable * If they are not then they must not be changed after adding to the MultiKey. * * @param key1 the first key * @param key2 the second key * @param key3 the third key */ @SuppressWarnings("unchecked") public MultiKey(final K key1, final K key2, final K key3) { this((K[]) new Object[] {key1, key2, key3}, false); } /** * Constructor taking four keys. *

* The keys should be immutable * If they are not then they must not be changed after adding to the MultiKey. * * @param key1 the first key * @param key2 the second key * @param key3 the third key * @param key4 the fourth key */ @SuppressWarnings("unchecked") public MultiKey(final K key1, final K key2, final K key3, final K key4) { this((K[]) new Object[] {key1, key2, key3, key4}, false); } /** * Constructor taking five keys. *

* The keys should be immutable * If they are not then they must not be changed after adding to the MultiKey. * * @param key1 the first key * @param key2 the second key * @param key3 the third key * @param key4 the fourth key * @param key5 the fifth key */ @SuppressWarnings("unchecked") public MultiKey(final K key1, final K key2, final K key3, final K key4, final K key5) { this((K[]) new Object[] {key1, key2, key3, key4, key5}, false); } /** * Constructor taking an array of keys which is cloned. *

* The keys should be immutable * If they are not then they must not be changed after adding to the MultiKey. *

* This is equivalent to new MultiKey(keys, true). * * @param keys the array of keys, not null * @throws IllegalArgumentException if the key array is null */ public MultiKey(final K[] keys) { this(keys, true); } /** * Constructor taking an array of keys, optionally choosing whether to clone. *

* If the array is not cloned, then it must not be modified. *

* This method is public for performance reasons only, to avoid a clone. * The hashcode is calculated once here in this method. * Therefore, changing the array passed in would not change the hashcode but * would change the equals method, which is a bug. *

* This is the only fully safe usage of this constructor, as the object array * is never made available in a variable: *

     * new MultiKey(new Object[] {...}, false);
     * 
*

* The keys should be immutable * If they are not then they must not be changed after adding to the MultiKey. * * @param keys the array of keys, not null * @param makeClone true to clone the array, false to assign it * @throws IllegalArgumentException if the key array is null * @since 3.1 */ public MultiKey(final K[] keys, final boolean makeClone) { super(); if (keys == null) { throw new IllegalArgumentException("The array of keys must not be null"); } if (makeClone) { this.keys = keys.clone(); } else { this.keys = keys; } calculateHashCode(keys); } //----------------------------------------------------------------------- /** * Gets a clone of the array of keys. *

* The keys should be immutable * If they are not then they must not be changed. * * @return the individual keys */ public K[] getKeys() { return keys.clone(); } /** * Gets the key at the specified index. *

* The key should be immutable. * If it is not then it must not be changed. * * @param index the index to retrieve * @return the key at the index * @throws IndexOutOfBoundsException if the index is invalid * @since 3.1 */ public K getKey(final int index) { return keys[index]; } /** * Gets the size of the list of keys. * * @return the size of the list of keys * @since 3.1 */ public int size() { return keys.length; } //----------------------------------------------------------------------- /** * Compares this object to another. *

* To be equal, the other object must be a MultiKey with the * same number of keys which are also equal. * * @param other the other object to compare to * @return true if equal */ @Override public boolean equals(final Object other) { if (other == this) { return true; } if (other instanceof MultiKey) { final MultiKey otherMulti = (MultiKey) other; return Arrays.equals(keys, otherMulti.keys); } return false; } /** * Gets the combined hash code that is computed from all the keys. *

* This value is computed once and then cached, so elements should not * change their hash codes once created (note that this is the same * constraint that would be used if the individual keys elements were * themselves {@link java.util.Map Map} keys. * * @return the hash code */ @Override public int hashCode() { return hashCode; } /** * Gets a debugging string version of the key. * * @return a debugging string */ @Override public String toString() { return "MultiKey" + Arrays.toString(keys); } /** * Calculate the hash code of the instance using the provided keys. * @param keys the keys to calculate the hash code for */ private void calculateHashCode(final Object[] keys) { int total = 0; for (final Object key : keys) { if (key != null) { total ^= key.hashCode(); } } hashCode = total; } /** * Recalculate the hash code after deserialization. The hash code of some * keys might have change (hash codes based on the system hash code are * only stable for the same process). * @return the instance with recalculated hash code */ protected Object readResolve() { calculateHashCode(keys); return this; } }





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