public class

MultiHashMap

extends HashMap<K, V>
implements MultiMap
java.lang.Object
   ↳ java.util.AbstractMap<K, V>
     ↳ java.util.HashMap<K, V>
       ↳ org.apache.commons.collections.MultiHashMap

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

Class Overview

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".

Summary

Public Constructors
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.
Public Methods
void clear()
Clear the map.
Object clone()
Clones the map creating an independent copy.
boolean containsValue(Object key, Object value)
Checks whether the collection at the specified key contains the value.
boolean containsValue(Object value)
Checks whether the map contains the value specified.
Collection getCollection(Object key)
Gets the collection mapped to the specified key.
Iterator iterator(Object key)
Gets an iterator for the collection mapped to the specified key.
Object put(Object key, Object value)
Adds the value to the collection associated with the specified key.
void putAll(Map map)
Override superclass to ensure that MultiMap instances are correctly handled.
boolean putAll(Object key, Collection values)
Adds a collection of values to the collection associated with the specified key.
Object remove(Object key, Object item)
Removes a specific value from map.
int size(Object key)
Gets the size of the collection mapped to the specified key.
int totalSize()
Gets the total size of the map by counting all the values.
Collection values()
Gets a collection containing all the values in the map.
Protected Methods
Collection createCollection(Collection coll)
Creates a new instance of the map value Collection container.
[Expand]
Inherited Methods
From class java.util.HashMap
From class java.util.AbstractMap
From class java.lang.Object
From interface java.util.Map
From interface org.apache.commons.collections.MultiMap

Public Constructors

public MultiHashMap ()

Constructor.

public MultiHashMap (int initialCapacity)

Constructor.

Parameters
initialCapacity the initial map capacity

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

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

Public Methods

public void clear ()

Clear the map.

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

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

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

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

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

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

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

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)

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

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

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

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

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

Protected Methods

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