org.apache.commons.collections.map
Class SingletonMap<K,V>

java.lang.Object
  org.apache.commons.collections.map.SingletonMap<K,V>

All Implemented Interfaces:

Serializable, Cloneable, Map<K,V>, BoundedMap<K,V>, IterableMap<K,V>, KeyValue<K,V>, OrderedMap<K,V>

public class SingletonMap<K,V>
extends Object
implements OrderedMap<K,V>, BoundedMap<K,V>, KeyValue<K,V>, Serializable, Cloneable

A Map implementation that holds a single item and is fixed size.

The single key/value pair is specified at creation. The map is fixed size so any action that would change the size is disallowed. However, the put or setValue methods can change the value associated with the key.

If trying to remove or clear the map, an UnsupportedOperationException is thrown. If trying to put a new mapping into the map, an IllegalArgumentException is thrown. The put method will only suceed if the key specified is the same as the singleton key.

The key and value can be obtained by:

• normal Map methods and views
• the MapIterator, see mapIterator()
• the KeyValue interface (just cast - no object creation)

Since:

Commons Collections 3.1

Version:

$Revision: 1.1.1.1 $ $Date: 2005/05/23 04:36:10 $

Author:

Matt Hall, John Watkinson, Stephen Colebourne

See Also:

Serialized Form

Nested Class Summary

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

Map.Entry<K,V>

Constructor Summary

SingletonMap()
Constructor that creates a map of null to null.

SingletonMap(KeyValue<K,V> keyValue)
Constructor specifying the key and value as a KeyValue.

SingletonMap(K key, V value)
Constructor specifying the key and value.

SingletonMap(Map.Entry<K,V> entry)
Constructor specifying the key and value as a MapEntry.

SingletonMap(Map<? extends K,? extends V> map)
Constructor copying elements from another map.

Method Summary

void	clear() Unsupported operation.
Object	clone() Clones the map without cloning the key or value.
boolean	containsKey(Object key) Checks whether the map contains the specified key.
boolean	containsValue(Object value) Checks whether the map contains the specified value.
Set<Map.Entry<K,V>>	entrySet() Gets the entrySet view of the map.
boolean	equals(Object obj) Compares this map with another.
K	firstKey() Gets the first (and only) key in the map.
V	get(Object key) Gets the value mapped to the key specified.
K	getKey() Gets the key.
V	getValue() Gets the value.
int	hashCode() Gets the standard Map hashCode.
boolean	isEmpty() Checks whether the map is currently empty, which it never is.
protected boolean	isEqualKey(Object key) Compares the specified key to the stored key.
protected boolean	isEqualValue(Object value) Compares the specified value to the stored value.
boolean	isFull() Is the map currently full, always true.
Set<K>	keySet() Gets the unmodifiable keySet view of the map.
K	lastKey() Gets the last (and only) key in the map.
MapIterator<K,V>	mapIterator() Gets an iterator over the map.
int	maxSize() Gets the maximum size of the map, always 1.
K	nextKey(K key) Gets the next key after the key specified, always null.
OrderedMapIterator<K,V>	orderedMapIterator() Obtains an OrderedMapIterator over the map.
K	previousKey(K key) Gets the previous key before the key specified, always null.
V	put(K key, V value) Puts a key-value mapping into this map where the key must match the existing key.
void	putAll(Map<? extends K,? extends V> map) Puts the values from the specified map into this map.
V	remove(Object key) Unsupported operation.
V	setValue(V value) Sets the value.
int	size() Gets the size of the map, always 1.
String	toString() Gets the map as a String.
Collection<V>	values() Gets the unmodifiable values view of the map.

Methods inherited from class java.lang.Object

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

Constructor Detail

SingletonMap

public SingletonMap()

Constructor that creates a map of null to null.

SingletonMap

public SingletonMap(K key,
                    V value)

Constructor specifying the key and value.

Parameters:

key - the key to use

value - the value to use

SingletonMap

public SingletonMap(KeyValue<K,V> keyValue)

Constructor specifying the key and value as a KeyValue.

Parameters:

keyValue - the key value pair to use

SingletonMap

public SingletonMap(Map.Entry<K,V> entry)

Constructor specifying the key and value as a MapEntry.

Parameters:

entry - the key value pair to use

SingletonMap

public SingletonMap(Map<? extends K,? extends V> map)

Constructor copying elements from another map.

Parameters:

map - the map to copy, must be size 1

Throws:

NullPointerException - if the map is null

IllegalArgumentException - if the size is not 1

Method Detail

getKey

public K getKey()

Gets the key.

Specified by:

getKey in interface KeyValue<K,V>

Returns:

the key

getValue

public V getValue()

Gets the value.

Specified by:

getValue in interface KeyValue<K,V>

Returns:

the value

setValue

public V setValue(V value)

Sets the value.

Parameters:

value - the new value to set

Returns:

the old value

isFull

public boolean isFull()

Is the map currently full, always true.

Specified by:

isFull in interface BoundedMap<K,V>

Returns:

true always

maxSize

public int maxSize()

Gets the maximum size of the map, always 1.

Specified by:

maxSize in interface BoundedMap<K,V>

Returns:

1 always

get

public V get(Object key)

Gets the value mapped to the key specified.

Specified by:

get in interface Map<K,V>

Parameters:

key - the key

Returns:

the mapped value, null if no match

size

public int size()

Gets the size of the map, always 1.

Specified by:

size in interface Map<K,V>

Returns:

the size of 1

isEmpty

public boolean isEmpty()

Checks whether the map is currently empty, which it never is.

Specified by:

isEmpty in interface Map<K,V>

Returns:

false always

containsKey

public boolean containsKey(Object key)

Checks whether the map contains the specified key.

Specified by:

containsKey in interface Map<K,V>

Parameters:

key - the key to search for

Returns:

true if the map contains the key

containsValue

public boolean containsValue(Object value)

Checks whether the map contains the specified value.

Specified by:

containsValue in interface Map<K,V>

Parameters:

value - the value to search for

Returns:

true if the map contains the key

put

public V put(K key,
             V value)

Puts a key-value mapping into this map where the key must match the existing key.

An IllegalArgumentException is thrown if the key does not match as the map is fixed size.

Specified by:

put in interface Map<K,V>

Parameters:

key - the key to set, must be the key of the map

value - the value to set

Returns:

the value previously mapped to this key, null if none

Throws:

IllegalArgumentException - if the key does not match

putAll

public void putAll(Map<? extends K,? extends V> map)

Puts the values from the specified map into this map.

The map must be of size 0 or size 1. If it is size 1, the key must match the key of this map otherwise an IllegalArgumentException is thrown.

Specified by:

putAll in interface Map<K,V>

Parameters:

map - the map to add, must be size 0 or 1, and the key must match

Throws:

NullPointerException - if the map is null

IllegalArgumentException - if the key does not match

remove

public V remove(Object key)

Unsupported operation.

Specified by:

remove in interface Map<K,V>

Parameters:

key - the mapping to remove

Returns:

the value mapped to the removed key, null if key not in map

Throws:

UnsupportedOperationException - always

clear

public void clear()

Unsupported operation.

Specified by:

clear in interface Map<K,V>

entrySet

public Set<Map.Entry<K,V>> entrySet()

Gets the entrySet view of the map. Changes made via setValue affect this map. To simply iterate through the entries, use mapIterator().

Specified by:

entrySet in interface Map<K,V>

Returns:

the entrySet view

keySet

public Set<K> keySet()

Gets the unmodifiable keySet view of the map. Changes made to the view affect this map. To simply iterate through the keys, use mapIterator().

Specified by:

keySet in interface Map<K,V>

Returns:

the keySet view

values

public Collection<V> values()

Gets the unmodifiable values view of the map. Changes made to the view affect this map. To simply iterate through the values, use mapIterator().

Specified by:

values in interface Map<K,V>

Returns:

the values view

mapIterator

public MapIterator<K,V> mapIterator()

Gets an iterator over the map. Changes made to the iterator using setValue affect this map. The remove method is unsupported.

A MapIterator returns the keys in the map. It also provides convenient methods to get the key and value, and set the value. It avoids the need to create an entrySet/keySet/values object. It also avoids creating the Map Entry object.

Specified by:

mapIterator in interface IterableMap<K,V>

Returns:

the map iterator

orderedMapIterator

public OrderedMapIterator<K,V> orderedMapIterator()

Obtains an OrderedMapIterator over the map.

A ordered map iterator is an efficient way of iterating over maps in both directions.

Specified by:

orderedMapIterator in interface OrderedMap<K,V>

Returns:

an ordered map iterator

firstKey

public K firstKey()

Gets the first (and only) key in the map.

Specified by:

firstKey in interface OrderedMap<K,V>

Returns:

the key

lastKey

public K lastKey()

Gets the last (and only) key in the map.

Specified by:

lastKey in interface OrderedMap<K,V>

Returns:

the key

nextKey

public K nextKey(K key)

Gets the next key after the key specified, always null.

Specified by:

nextKey in interface OrderedMap<K,V>

Parameters:

key - the next key

Returns:

null always

previousKey

public K previousKey(K key)

Gets the previous key before the key specified, always null.

Specified by:

previousKey in interface OrderedMap<K,V>

Parameters:

key - the next key

Returns:

null always

isEqualKey

protected boolean isEqualKey(Object key)

Compares the specified key to the stored key.

Parameters:

key - the key to compare

Returns:

true if equal

isEqualValue

protected boolean isEqualValue(Object value)

Compares the specified value to the stored value.

Parameters:

value - the value to compare

Returns:

true if equal

clone

public Object clone()

Clones the map without cloning the key or value.

Overrides:

clone in class Object

Returns:

a shallow clone

equals

public boolean equals(Object obj)

Compares this map with another.

Specified by:

equals in interface Map<K,V>

Overrides:

equals in class Object

Parameters:

obj - the object to compare to

Returns:

true if equal

hashCode

public int hashCode()

Gets the standard Map hashCode.

Specified by:

hashCode in interface Map<K,V>

Overrides:

hashCode in class Object

Returns:

the hash code defined in the Map interface

toString

public String toString()

Gets the map as a String.

Overrides:

toString in class Object

Returns:

a string version of the map