com.neoworks.util
Class HashMapMultiMap

java.lang.Object
  |
  +--com.neoworks.util.HashMapMultiMap

All Implemented Interfaces:

MultiMap

public class HashMapMultiMap

extends java.lang.Object

implements MultiMap

HashMapMultiMap is a Multimap backed by a HashMap of Set objects. This means it differs from a standard MultiMap in a few important ways.

• It cannot contain duplicate entries in the keys
• It cannot contain duplicates in the values
• It might even be in any way quick

Version:

$Revision: 1.2 $

Author:

nick@neoworks.com

Nested Class Summary

Nested classes inherited from class com.neoworks.util.MultiMap

MultiMap.Entry

Constructor Summary

HashMapMultiMap()
Public constructor

Method Summary

void	clear() Removes all mappings from this multimap (optional operation).
boolean	containsKey(java.lang.Object key) Returns true if this multimap contains a mapping for the specified key.
boolean	containsValue(java.lang.Object value) Returns true if this multimap maps one or more keys to the specified value.
java.util.Set	entrySet() Get the EntrySet.
boolean	equals(java.lang.Object o) Compares the specified object with this multimap for equality.
java.util.Set	get(java.lang.Object key) Returns the set of values to which this multimap maps the specified key.
int	hashCode() Returns the hash code value for this multimap.
boolean	isEmpty() Returns true if this multimap contains no key-value mappings.
java.util.Collection	keys() Returns a collection view of the keys contained in this multimap.
java.util.Set	put(java.lang.Object key, java.lang.Object value) Associates the specified value with the specified key in this multimap (optional operation).
void	putAll(MultiMap multimap) Copies all of the mappings from the specified multimap to this multimap (optional operation).
java.util.Set	remove(java.lang.Object key) Removes all the mappings for this key from this multimap if present (optional operation).
java.lang.Object	remove(java.lang.Object key, java.lang.Object value) Removes the (key, value) mapping from this multimap if present (optional operation).
int	size() Returns the number of key-values mappings in this multimap.
java.util.Collection	uniqueKeys() Returns a collection of the unique keys in this multimap.
java.util.Collection	values() Returns a collection view of the values contained in this multimap.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

HashMapMultiMap

public HashMapMultiMap()

Public constructor

Method Detail

put

public java.util.Set put(java.lang.Object key,
                         java.lang.Object value)
                  throws java.lang.UnsupportedOperationException,
                         java.lang.ClassCastException,
                         java.lang.IllegalArgumentException,
                         java.lang.NullPointerException

Associates the specified value with the specified key in this multimap (optional operation). If the multimap previously contained a mapping for this key this mapping is not lost.

Specified by:

put in interface MultiMap

Parameters:

key - Key with which the specified value is to be associated.

value - Value to be associated with the specified key.

Returns:

Set of values associated with the specified key (including the new addition).

Throws:

java.lang.UnsupportedOperationException - If the put operation is not supported by this multimap.

java.lang.ClassCastException - If the class of the specified key or value prevents it from being stored in this multimap.

java.lang.IllegalArgumentException - If some aspect of this key or value prevents it from being stored in this multimap.

java.lang.NullPointerException - This multimap does not permit null keys or values, and the specified key or value is null.

keys

public java.util.Collection keys()

Returns a collection view of the keys contained in this multimap. The collection is backed by the multimap, so changes to the multimap are reflected in the collection, and vice-versa. If the multimap is modified while an iteration over the collection is in progress, the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the multimap, via the Iterator.remove, Collection.remove, removeAll retainAll, and clear operations. It does not support the add or addAll operations. This implementation does not return duplicate keys in the keyset.

Specified by:

keys in interface MultiMap

Returns:

A collection view of the keys contained in this multimap.

remove

public java.util.Set remove(java.lang.Object key)
                     throws java.lang.UnsupportedOperationException

Removes all the mappings for this key from this multimap if present (optional operation).

Specified by:

remove in interface MultiMap

Parameters:

key - Key whose mappings is to be removed from the multimap.

Returns:

Set of values associated with the specified key, or null if there were no mappings for key.

Throws:

java.lang.UnsupportedOperationException - If the remove operation is not supported by this multimap.

clear

public void clear()
           throws java.lang.UnsupportedOperationException

Removes all mappings from this multimap (optional operation).

Specified by:

clear in interface MultiMap

Throws:

java.lang.UnsupportedOperationException - If clear is not supported by this multimap.

values

public java.util.Collection values()

Returns a collection view of the values contained in this multimap. The collection is backed by the multimap, so changes to the multimap are reflected in the collection, and vice-versa. If the multimap is modified while an iteration over the collection is in progress, the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the multimap, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Specified by:

values in interface MultiMap

Returns:

A collection view of the values contained in this multimap.

entrySet

public java.util.Set entrySet()

Get the EntrySet. This is pretty pointless for this particular implementation, but is included because it's in the interface.

Specified by:

entrySet in interface MultiMap

Returns:

A set of entries

hashCode

public int hashCode()

Returns the hash code value for this multimap. The hash code of a multimap is defined to be the sum of the hashCodes of each entry in the multimap's entrySet view. This ensures that t1.equals(t2) implies that t1.hashCode()==t2.hashCode() for any two multimaps t1 and t2, as required by the general contract of Object.hashCode.

Specified by:

hashCode in interface MultiMap

Overrides:

hashCode in class java.lang.Object

Returns:

The hash code value for this multimap.

containsKey

public boolean containsKey(java.lang.Object key)
                    throws java.lang.ClassCastException,
                           java.lang.NullPointerException

Returns true if this multimap contains a mapping for the specified key.

Specified by:

containsKey in interface MultiMap

Parameters:

key - Key whose presence in this multimap is to be tested.

Returns:

true if this multimap contains a mapping for the specified key.

Throws:

java.lang.ClassCastException - If the key is of an inappropriate type for this multimap.

java.lang.NullPointerException - If the key is null and this multimap does not not permit null keys

putAll

public void putAll(MultiMap multimap)
            throws java.lang.UnsupportedOperationException,
                   java.lang.ClassCastException,
                   java.lang.IllegalArgumentException,
                   java.lang.NullPointerException

Copies all of the mappings from the specified multimap to this multimap (optional operation). These mappings will replace any mappings that this multimap had for any of the keys currently in the specified multimap.

Specified by:

putAll in interface MultiMap

Parameters:

multimap - Mappings to be stored in this multimap.

Throws:

java.lang.UnsupportedOperationException - If the put operation is not supported by this multimap.

java.lang.ClassCastException - If the class of the specified key or value prevents it from being stored in this multimap.

java.lang.IllegalArgumentException - If some aspect of a key or value in the specified multimap prevents it from being stored in this multimap.

java.lang.NullPointerException - This multimap does not permit null keys or values, and the specified key or value is null.

size

public int size()

Returns the number of key-values mappings in this multimap. If the multimap contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Specified by:

size in interface MultiMap

Returns:

The number of key-values mappings in this multimap

uniqueKeys

public java.util.Collection uniqueKeys()

Returns a collection of the unique keys in this multimap.

Specified by:

uniqueKeys in interface MultiMap

Returns:

A Collection of unique keys

remove

public java.lang.Object remove(java.lang.Object key,
                               java.lang.Object value)
                        throws java.lang.UnsupportedOperationException

Removes the (key, value) mapping from this multimap if present (optional operation).

Specified by:

remove in interface MultiMap

Parameters:

value - The value associated with the key to identify the item to remove

key - Key whose mapping to the value is to be removed from the multimap.

Returns:

Value that was unmapped from the specified key, or null if the given mapping did not exist.

Throws:

java.lang.UnsupportedOperationException - If the remove operation is not supported by this multimap.

containsValue

public boolean containsValue(java.lang.Object value)

Returns true if this multimap maps one or more keys to the specified value. More formally, returns true if and only if this multimap contains at least one mapping to a value v such that (value==null ? v==null : value.equals(v)). This operation will probably require time linear in the multimap size for most implementations of the MultiMap interface.

Specified by:

containsValue in interface MultiMap

Parameters:

value - Value whose presence in this multimap is to be tested.

Returns:

true if this multimap maps one or more keys to the specified value.

equals

public boolean equals(java.lang.Object o)

Compares the specified object with this multimap for equality. Returns true if the given object is also a multimap and the two multimaps represent the same mappings. More formally, two maps t1 and t2 represent the same mappings if t1.entrySet().equals(t2.entrySet()). This ensures that the equals method works properly across different implementations of the MultiMap interface.

Specified by:

equals in interface MultiMap

Overrides:

equals in class java.lang.Object

Parameters:

o - Object to be compared for equality with this multimap.

Returns:

true if the specified object is equal to this multimap.

get

public java.util.Set get(java.lang.Object key)
                  throws java.lang.ClassCastException,
                         java.lang.NullPointerException

Returns the set of values to which this multimap maps the specified key. Returns null if the multimap contains no mappings for this key. A return value of null does indicate that the multimap contains no mappings for the key; it's possible that the multimap explicitly maps the key to null, in this case the returned set will contain null possibly along with other objects. The containsKey operation may also be used to distinguish these two cases.

Specified by:

get in interface MultiMap

Parameters:

key - Key whose associated value is to be returned.

Returns:

A Set of values to which this multimap maps the specified key, or null if the multimap contains no mapping for this key.

Throws:

java.lang.ClassCastException - If the key is of an inappropriate type for this multimap.

java.lang.NullPointerException - If the key is null and this multimap does not not permit null keys

isEmpty

public boolean isEmpty()

Returns true if this multimap contains no key-value mappings.

Specified by:

isEmpty in interface MultiMap

Returns:

true if this multimap contains no key-value mappings.