org.apache.commons.collections

Class MultiHashMap

public class MultiHashMap extends HashMap implements MultiMap

Deprecated: Class now available as MultiValueMap in map subpackage. This version is due to be removed in collections v4.0.

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 return a Collection, holding all the values put to that key.

This implementation uses an ArrayList as the collection. The internal storage list is made available without cloning via the get(Object) and entrySet() methods. The implementation returns null when there are no values mapped to a key.

For example:

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

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

Since: Commons Collections 2.0

Version: $Revision: 372373 $ $Date: 2006-01-26 00:10:43 +0000 (Thu, 26 Jan 2006) $

Author: Christopher Berry James Strachan Steve Downey Stephen Colebourne Julien Buret Serhiy Yevtushenko Robert Ribnitz

Constructor Summary
MultiHashMap()
Constructor.
MultiHashMap(int initialCapacity)
Constructor.
MultiHashMap(int initialCapacity, float loadFactor)
Constructor.
MultiHashMap(Map mapToCopy)
Constructor that copies the input map creating an independent copy.
Method Summary
voidclear()
Clear the map.
Objectclone()
Clones the map creating an independent copy.
booleancontainsValue(Object value)
Checks whether the map contains the value specified.
booleancontainsValue(Object key, Object value)
Checks whether the collection at the specified key contains the value.
protected CollectioncreateCollection(Collection coll)
Creates a new instance of the map value Collection container.
CollectiongetCollection(Object key)
Gets the collection mapped to the specified key.
Iteratoriterator(Object key)
Gets an iterator for the collection mapped to the specified key.
Objectput(Object key, Object value)
Adds the value to the collection associated with the specified key.
voidputAll(Map map)
Override superclass to ensure that MultiMap instances are correctly handled.
booleanputAll(Object key, Collection values)
Adds a collection of values to the collection associated with the specified key.
Objectremove(Object key, Object item)
Removes a specific value from map.
intsize(Object key)
Gets the size of the collection mapped to the specified key.
inttotalSize()
Gets the total size of the map by counting all the values.
Collectionvalues()
Gets a collection containing all the values in the map.

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 that copies the input map creating an independent copy.

This method performs different behaviour depending on whether the map specified is a MultiMap or not. If a MultiMap is specified, each internal collection is also cloned. If the specified map only implements Map, then the values are not cloned.

NOTE: From Commons Collections 3.1 this method correctly copies a MultiMap to form a truly independent new map. NOTE: From Commons Collections 3.2 this method delegates to the newly added putAll(Map) override method.

Parameters: mapToCopy a Map to copy

Method Detail

clear

public void clear()
Clear the map.

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

clone

public Object clone()
Clones the map creating an independent copy.

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

Returns: the cloned map

containsValue

public boolean containsValue(Object value)
Checks whether the map contains the value specified.

This checks all collections against all keys for the value, and thus could be slow.

Parameters: value the value to search for

Returns: true if the map contains the value

containsValue

public boolean containsValue(Object key, Object value)
Checks whether the collection at the specified key contains the value.

Parameters: value the value to search for

Returns: true if the map contains the value

Since: Commons Collections 3.1

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

getCollection

public Collection getCollection(Object key)
Gets the collection mapped to the specified key. This method is a convenience method to typecast the result of get(key).

Parameters: key the key to retrieve

Returns: the collection mapped to the key, null if no mapping

Since: Commons Collections 3.1

iterator

public Iterator iterator(Object key)
Gets an iterator for the collection mapped to the specified key.

Parameters: key the key to get an iterator for

Returns: the iterator of the collection at the key, empty iterator if key not in map

Since: Commons Collections 3.1

put

public Object put(Object key, Object value)
Adds the value to the collection associated with the specified key.

Unlike a normal Map the previous value is not replaced. Instead the new value is added to the collection stored against the key.

Parameters: key the key to store against value the value to add to the collection at the key

Returns: the value added if the map changed and null if the map did not change

putAll

public void putAll(Map map)
Override superclass to ensure that MultiMap instances are correctly handled.

NOTE: Prior to version 3.2, putAll(map) did not work properly when passed a MultiMap.

Parameters: map the map to copy (either a normal or multi map)

putAll

public boolean putAll(Object key, Collection values)
Adds a collection of values to the collection associated with the specified key.

Parameters: key the key to store against values the values to add to the collection at the key, null ignored

Returns: true if this map changed

Since: Commons Collections 3.1

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. Other values attached to that key are unaffected.

If the last value for a key is removed, null will be returned from a subsequant get(key).

Parameters: key the key to remove from item the value to remove

Returns: the value removed (which was passed in), null if nothing removed

size

public int size(Object key)
Gets the size of the collection mapped to the specified key.

Parameters: key the key to get size for

Returns: the size of the collection at the key, zero if key not in map

Since: Commons Collections 3.1

totalSize

public int totalSize()
Gets the total size of the map by counting all the values.

Returns: the total size of the map counting all values

Since: Commons Collections 3.1

values

public Collection values()
Gets a collection containing all the values in the map.

This returns a collection containing the combination of values from all keys.

Returns: a collection view of the values contained in this map

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