org.apache.commons.collections.keyvalue

Class MultiKey

Implemented Interfaces:
Serializable

public class MultiKey
extends java.lang.Object
implements Serializable

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 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.

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 retireve the localized text
 MultiKey multiKey = new MultiKey(key, locale);
 String localizedText = (String) map.get(multiKey);
 
Version:
$Revision: 1.5 $ $Date: 2004/03/13 12:43:43 $
Authors:
Howard Lewis Ship
Stephen Colebourne
Since:
Commons Collections 3.0

Constructor Summary

MultiKey(Object key1, Object key2)
Constructor taking two keys.
MultiKey(Object key1, Object key2, Object key3)
Constructor taking three keys.
MultiKey(Object key1, Object key2, Object key3, Object key4)
Constructor taking four keys.
MultiKey(Object key1, Object key2, Object key3, Object key4, Object key5)
Constructor taking five keys.
MultiKey(Object[] keys)
Constructor taking an array of keys which is cloned.
MultiKey(Object[] keys, boolean makeClone)
Constructor taking an array of keys, optionally choosing whether to clone.

Method Summary

boolean
equals(Object other)
Compares this object to another.
Object
getKey(int index)
Gets the key at the specified index.
Object[]
getKeys()
Gets a clone of the array of keys.
int
hashCode()
Gets the combined hash code that is computed from all the keys.
int
size()
Gets the size of the list of keys.
String
toString()
Gets a debugging string version of the key.

Constructor Details

MultiKey

public MultiKey(Object key1,
                Object key2)
Constructor taking two keys.

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

Parameters:
key1 - the first key
key2 - the second key

MultiKey

public MultiKey(Object key1,
                Object key2,
                Object key3)
Constructor taking three keys.

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

Parameters:
key1 - the first key
key2 - the second key
key3 - the third key

MultiKey

public MultiKey(Object key1,
                Object key2,
                Object key3,
                Object key4)
Constructor taking four keys.

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

Parameters:
key1 - the first key
key2 - the second key
key3 - the third key
key4 - the fourth key

MultiKey

public MultiKey(Object key1,
                Object key2,
                Object key3,
                Object key4,
                Object key5)
Constructor taking five keys.

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

Parameters:
key1 - the first key
key2 - the second key
key3 - the third key
key4 - the fourth key
key5 - the fifth key

MultiKey

public MultiKey(Object[] keys)
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).

Parameters:
keys - the array of keys, not null

MultiKey

public MultiKey(Object[] keys,
                boolean makeClone)
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.

Parameters:
keys - the array of keys, not null
makeClone - true to clone the array, false to assign it
Since:
Commons Collections 3.1

Method Details

equals

public boolean equals(Object other)
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.

Parameters:
other - the other object to compare to
Returns:
true if equal

getKey

public Object getKey(int index)
Gets the key at the specified index.

The key should be immutable. If it is not then it must not be changed.

Parameters:
index - the index to retrieve
Returns:
the key at the index
Since:
Commons Collections 3.1

getKeys

public Object[] getKeys()
Gets a clone of the array of keys.

The keys should be immutable If they are not then they must not be changed.

Returns:
the individual keys

hashCode

public int hashCode()
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 Map keys.

Returns:
the hash code

size

public int size()
Gets the size of the list of keys.
Returns:
the size of the list of keys
Since:
Commons Collections 3.1

toString

public String toString()
Gets a debugging string version of the key.
Returns:
a debugging string

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