/*
* Copyright 2003-2004 The Apache Software Foundation
*
* Licensed 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.keyvalue;
import java.io.Serializable;
import java.util.Arrays;
/**
* A <code>MultiKey</code> allows multiple map keys to be merged together.
* <p>
* 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 lookup a filename 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.
* <p>
* Example usage:
* <pre>
* // populate map with data mapping key+locale to localizedText
* Map map = new HashMap();
* MultiKey multiKey = new MultiKey(key, locale);
* map.put(multiKey, localizedText);
*
* // later retireve the localized text
* MultiKey multiKey = new MultiKey(key, locale);
* String localizedText = (String) map.get(multiKey);
* </pre>
*
* @since Commons Collections 3.0
* @version $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
*
* @author Howard Lewis Ship
* @author Stephen Colebourne
*/
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 Object[] keys;
/** The cached hashCode */
private final int hashCode;
/**
* Constructor taking two keys.
* <p>
* 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
*/
public MultiKey(Object key1, Object key2) {
this(new Object[] {key1, key2}, false);
}
/**
* Constructor taking three keys.
* <p>
* 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
*/
public MultiKey(Object key1, Object key2, Object key3) {
this(new Object[] {key1, key2, key3}, false);
}
/**
* Constructor taking four keys.
* <p>
* 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
*/
public MultiKey(Object key1, Object key2, Object key3, Object key4) {
this(new Object[] {key1, key2, key3, key4}, false);
}
/**
* Constructor taking five keys.
* <p>
* 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
*/
public MultiKey(Object key1, Object key2, Object key3, Object key4, Object key5) {
this(new Object[] {key1, key2, key3, key4, key5}, false);
}
/**
* Constructor taking an array of keys which is cloned.
* <p>
* The keys should be immutable
* If they are not then they must not be changed after adding to the MultiKey.
* <p>
* This is equivalent to <code>new MultiKey(keys, true)</code>.
*
* @param keys the array of keys, not null
* @throws IllegalArgumentException if the key array is null
*/
public MultiKey(Object[] keys) {
this(keys, true);
}
/**
* Constructor taking an array of keys, optionally choosing whether to clone.
* <p>
* <b>If the array is not cloned, then it must not be modified.</b>
* <p>
* 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.
* <p>
* This is the only fully safe usage of this constructor, as the object array
* is never made available in a variable:
* <pre>
* new MultiKey(new Object[] {...}, false);
* </pre>
* <p>
* 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 Commons Collections 3.1
*/
public MultiKey(Object[] keys, boolean makeClone) {
super();
if (keys == null) {
throw new IllegalArgumentException("The array of keys must not be null");
}
if (makeClone) {
this.keys = (Object[]) keys.clone();
} else {
this.keys = keys;
}
int total = 0;
for (int i = 0; i < keys.length; i++) {
if (keys[i] != null) {
total ^= keys[i].hashCode();
}
}
hashCode = total;
}
//-----------------------------------------------------------------------
/**
* Gets a clone of the array of keys.
* <p>
* The keys should be immutable
* If they are not then they must not be changed.
*
* @return the individual keys
*/
public Object[] getKeys() {
return (Object[]) keys.clone();
}
/**
* Gets the key at the specified index.
* <p>
* 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 Commons Collections 3.1
*/
public Object getKey(int index) {
return keys[index];
}
/**
* Gets the size of the list of keys.
*
* @return the size of the list of keys
* @since Commons Collections 3.1
*/
public int size() {
return keys.length;
}
//-----------------------------------------------------------------------
/**
* Compares this object to another.
* <p>
* To be equal, the other object must be a <code>MultiKey</code> with the
* same number of keys which are also equal.
*
* @param other the other object to compare to
* @return true if equal
*/
public boolean equals(Object other) {
if (other == this) {
return true;
}
if (other instanceof MultiKey) {
MultiKey otherMulti = (MultiKey) other;
return Arrays.equals(keys, otherMulti.keys);
}
return false;
}
/**
* Gets the combined hash code that is computed from all the keys.
* <p>
* 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
*/
public int hashCode() {
return hashCode;
}
/**
* Gets a debugging string version of the key.
*
* @return a debugging string
*/
public String toString() {
return "MultiKey" + Arrays.asList(keys).toString();
}
}