jwutil.collections
Interface MultiMap

All Superinterfaces:

BinaryRelation, java.util.Map

All Known Subinterfaces:

InvertibleMultiMap

All Known Implementing Classes:

GenericInvertibleMultiMap, GenericMultiMap, UnmodifiableMultiMap

public interface MultiMap
extends java.util.Map, BinaryRelation

MultiMap maps a key to a collection of values. These collections are created as needed using a CollectionFactory. Any constraints on the collections produced by this factory thus hold for the values that this maps to.
Formally, a MultiMap is a Multiple Associative Container. It associates key objects with value objects. The difference between a MultiMap and a standard Map is that MultiMap extends the Map interface to allow for the same key to map to multiple values.
Thus, the type signature for a MultiMap is :: Map[keytype -> [valtype] ]
Note that an association (known as a (Key, Value) pair or a Map.Entry in the Java Collections API) is only defined to exist if the collection of objects mapped to by some key is non-empty. This has a number of implications for the behavior of MultiMap:
Let

1. mm be a MultiMap,
2. k be an Object (which may or may not be a Key in mm)
3. c be the Collection returned by mm.getValues(k).

Then c will either be a non-empty Collection (the case where k is a Key in mm) or it will be an empty collection (the case where k is not a Key in mm). In the latter case, however, k is still considered to not be a Key in mm until c is made non-empty. We chose to return an empty Collection instead of null to allow for straightforward addition to the collection of values mapped to by k.
To conform to the Map interface, the put(key, value) method has a non-intuitive behavior; it throws away all values previously associated with key and creates a new mapping from key to a singleton collection containing value. Use add(key, value) to preserve the old collection of associative mappings.

Note that the behavior of MultiMap is indistinquishable from that of a Map if none of the extensions of MultiMap are utilized. Thus, users should take care to ensure that other code relying on the constraints enforced by the Map interface does not ever attempt to use a MultiMap when any of its Keys map to more than one value.

FSK: This data type is a bit experimental; a few changes may be coming:

1. We may make it not extend the Map interface, because it inherently violates the constraints of the Map interface once multiple values are added for one key.

The Collection views returned right now don't offer very much in terms of modifying the state of this internally.

Some of the views returned do not properly reflect modification in this. This is a gross oversight of Collection's interface on my part and I need to fix it, which I will do when I have free time.

Version:

$Id: MultiMap.java 1934 2004-09-27 22:42:35Z joewhaley $

Author:

Felix S. Klock II

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

java.util.Map.Entry<K,V>

Method Summary

boolean	add(java.lang.Object key, java.lang.Object value) Ensures that this contains an association from key to value.
boolean	addAll(MultiMap mm) Adds all mappings in the given multimap to this multimap.
boolean	addAll(java.lang.Object key, java.util.Collection values) Adds to the current mappings: associations for key to each value in values.
java.lang.String	computeHistogram(java.lang.String keyName, java.lang.String valueName)
boolean	contains(java.lang.Object a, java.lang.Object b) Returns true if a has a mapping to b in this.
java.util.Set	entrySet() Returns a Set view that allows you to recapture the MultiMap view.
java.lang.Object	get(java.lang.Object key) Returns some arbitrary value from the collection of values to which this map maps the specified key.
java.util.Collection	getValues(java.lang.Object key) Returns the collection of Values associated with key.
java.lang.Object	put(java.lang.Object key, java.lang.Object value) Associates the specified value with the specified key in this map, after removing all old values associated with the key.
void	putAll(java.util.Map t) Copies the mappings from the specified map to this map, after removing all old values associated with the key.
java.lang.Object	remove(java.lang.Object key) Removes mappings from key to all associated values from this map.
boolean	remove(java.lang.Object key, java.lang.Object value) Removes a mapping from key to value from this map if present.
boolean	removeAll(java.lang.Object key, java.util.Collection values) Removes from the current mappings: associations for key to any value in values.
boolean	retainAll(java.lang.Object key, java.util.Collection values) Removes from the current mappings: associations for key to any value not in values.
int	size() Returns the number of key-value mappings in this map (keys which map to multiple values count multiple times).

Methods inherited from interface java.util.Map

clear, containsKey, containsValue, equals, hashCode, isEmpty, keySet, values

Method Detail

get

java.lang.Object get(java.lang.Object key)

Returns some arbitrary value from the collection of values to which this map maps the specified key. Returns null if the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinquish these two cases. Note that if only the put method is used to modify this, then get will operate just as it would in any other Map.

Specified by:

get in interface java.util.Map

put

java.lang.Object put(java.lang.Object key,
                     java.lang.Object value)

Associates the specified value with the specified key in this map, after removing all old values associated with the key. Returns some value that was previously associated with the specified key, or null if no values were associated previously.

Specified by:

put in interface java.util.Map

putAll

void putAll(java.util.Map t)

Copies the mappings from the specified map to this map, after removing all old values associated with the key. Note that putAll(mm) where mm is a MultiMap will NOT add all of the mappings in mm; it will only add all of the Keys in mm, mapping each Key to one of the Values it mapped to in mm. To add all of the mappings from another MultiMap, use addAll(MultiMap).

Specified by:

putAll in interface java.util.Map

remove

java.lang.Object remove(java.lang.Object key)

Removes mappings from key to all associated values from this map. This is consistent with the Map definition of remove.

Specified by:

remove in interface java.util.Map

Returns:

one of the previous values associated with the key, or null if Map associated no values with the key. Note that a zero-sized collection is not returned in the latter case, and that a null return value may be ambiguous if the map associated null with the given key (in addition to possibly other values).

remove

boolean remove(java.lang.Object key,
               java.lang.Object value)

Removes a mapping from key to value from this map if present. (MultiMap specific operation). Note that if multiple mappings from key to value are permitted by this map, then only one is guaranteed to be removed. Returns true if this was modified as a result of this operation, else returns false.

add

boolean add(java.lang.Object key,
            java.lang.Object value)

Ensures that this contains an association from key to value. (MultiMap specific operation).

Returns:

true if this mapping changed as a result of the call

addAll

boolean addAll(java.lang.Object key,
               java.util.Collection values)

Adds to the current mappings: associations for key to each value in values. (MultiMap specific operation).

Returns:

true if this mapping changed as a result of the call

addAll

boolean addAll(MultiMap mm)

Adds all mappings in the given multimap to this multimap.

retainAll

boolean retainAll(java.lang.Object key,
                  java.util.Collection values)

Removes from the current mappings: associations for key to any value not in values. (MultiMap specific operation).

Returns:

true if this mapping changed as a result of the call

removeAll

boolean removeAll(java.lang.Object key,
                  java.util.Collection values)

Removes from the current mappings: associations for key to any value in values. (MultiMap specific operation).

Returns:

true if this mapping changed as a result of the call

getValues

java.util.Collection getValues(java.lang.Object key)

Returns the collection of Values associated with key. Modifications to the returned Collection affect this as well. If there are no Values currently associated with key, constructs a new, potentially mutable, empty Collection and returns it. (MultiMap specific operation).

contains

boolean contains(java.lang.Object a,
                 java.lang.Object b)

Returns true if a has a mapping to b in this. (MultiMap specific operation).

Specified by:

contains in interface BinaryRelation

size

int size()

Returns the number of key-value mappings in this map (keys which map to multiple values count multiple times).

Specified by:

size in interface java.util.Map

entrySet

java.util.Set entrySet()

Returns a Set view that allows you to recapture the MultiMap view.

Specified by:

entrySet in interface java.util.Map

computeHistogram

java.lang.String computeHistogram(java.lang.String keyName,
                                  java.lang.String valueName)