org.apache.commons.collections
Class MultiHashMap

java.lang.Object
  |
  +--java.util.AbstractMap
        |
        +--java.util.HashMap
              |
              +--org.apache.commons.collections.MultiHashMap

All Implemented Interfaces:

Cloneable, Map, MultiMap, Serializable

public class MultiHashMap

extends HashMap

implements MultiMap

MultiHashMap is the default implementation of the MultiMap interface.

A MultiMap is a Map with slightly different semantics. Putting a value into the map will add the value to a Collection at that key. Getting a value will always return a Collection, holding all the values put to that key. This implementation uses an ArrayList as the collection.

For example:

 MultiMap mhm = new MultiHashMap();
 mhm.put(key, "A");
 mhm.put(key, "B");
 mhm.put(key, "C");
 Collection coll = mhm.get(key);

coll will be a list containing "A", "B", "C".

Since:

Commons Collections 2.0

Version:

$Revision: 1.14 $ $Date: 2004/01/14 21:43:03 $

Author:

Christopher Berry, James Strachan, Steve Downey, Stephen Colebourne, Julien Buret, Serhiy Yevtushenko

See Also:

Serialized Form

Constructor Summary

MultiHashMap()
Constructor.

MultiHashMap(int initialCapacity)
Constructor.

MultiHashMap(int initialCapacity, float loadFactor)
Constructor.

MultiHashMap(Map mapToCopy)
Constructor.

Method Summary

void	clear() Clear the map.
Object	clone() Clone the map.
boolean	containsValue(Object value) Does the map contain a specific value.
protected Collection	createCollection(Collection coll) Creates a new instance of the map value Collection container.
Object	put(Object key, Object value) Put a key and value into the map.
Object	remove(Object key, Object item) Removes a specific value from map.
Collection	values() Gets a view over all the values in the map.

Methods inherited from class java.util.HashMap

containsKey, entrySet, get, isEmpty, keySet, putAll, remove, size

Methods inherited from class java.util.AbstractMap

equals, hashCode, toString

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

containsKey, entrySet, equals, get, hashCode, isEmpty, keySet, putAll, remove, size

Constructor Detail

MultiHashMap

public MultiHashMap()

Constructor.

MultiHashMap

public MultiHashMap(int initialCapacity)

Constructor.

Parameters:

initialCapacity - the initial map capacity

MultiHashMap

public MultiHashMap(int initialCapacity,
                    float loadFactor)

Constructor.

Parameters:

initialCapacity - the initial map capacity

loadFactor - the amount 0.0-1.0 at which to resize the map

MultiHashMap

public MultiHashMap(Map mapToCopy)

Constructor.

Parameters:

mapToCopy - a Map to copy

Method Detail

put

public Object put(Object key,
                  Object value)

Put a key and value into the map.

The value is added to a collection mapped to the key instead of replacing the previous value.

Specified by:

put in interface Map

Overrides:

put in class HashMap

Parameters:

key - the key to set

value - the value to set the key to

Returns:

the value added if the add is successful, null otherwise

containsValue

public boolean containsValue(Object value)

Does the map contain a specific value.

This searches the collection mapped to each key, and thus could be slow.

Specified by:

containsValue in interface Map

Overrides:

containsValue in class HashMap

Parameters:

value - the value to search for

Returns:

true if the list contains the value

remove

public Object remove(Object key,
                     Object item)

Removes a specific value from map.

The item is removed from the collection mapped to the specified key.

Specified by:

remove in interface MultiMap

Parameters:

key - the key to remove from

item - the value to remove

Returns:

the value removed (which was passed in)

clear

public void clear()

Clear the map.

This clears each collection in the map, and so may be slow.

Specified by:

clear in interface Map

Overrides:

clear in class HashMap

values

public Collection values()

Gets a view over all the values in the map.

The values view includes all the entries in the collections at each map key.

Specified by:

values in interface Map

Overrides:

values in class HashMap

Returns:

the collection view of all the values in the map

clone

public Object clone()

Clone the map.

The clone will shallow clone the collections as well as the map.

Overrides:

clone in class HashMap

Returns:

the cloned map

createCollection

protected Collection createCollection(Collection coll)

Creates a new instance of the map value Collection container.

This method can be overridden to use your own collection type.

Parameters:

coll - the collection to copy, may be null

Returns:

the new collection