org.apache.commons.collections.map

Class SingletonMap

public class SingletonMap extends Object implements OrderedMap, BoundedMap, KeyValue, 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:

Since: Commons Collections 3.1

Version: $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $

Author: Stephen Colebourne

Constructor Summary
SingletonMap()
Constructor that creates a map of null to null.
SingletonMap(Object key, Object value)
Constructor specifying the key and value.
SingletonMap(KeyValue keyValue)
Constructor specifying the key and value as a KeyValue.
SingletonMap(Entry mapEntry)
Constructor specifying the key and value as a MapEntry.
SingletonMap(Map map)
Constructor copying elements from another map.
Method Summary
voidclear()
Unsupported operation.
Objectclone()
Clones the map without cloning the key or value.
booleancontainsKey(Object key)
Checks whether the map contains the specified key.
booleancontainsValue(Object value)
Checks whether the map contains the specified value.
SetentrySet()
Gets the entrySet view of the map.
booleanequals(Object obj)
Compares this map with another.
ObjectfirstKey()
Gets the first (and only) key in the map.
Objectget(Object key)
Gets the value mapped to the key specified.
ObjectgetKey()
Gets the key.
ObjectgetValue()
Gets the value.
inthashCode()
Gets the standard Map hashCode.
booleanisEmpty()
Checks whether the map is currently empty, which it never is.
protected booleanisEqualKey(Object key)
Compares the specified key to the stored key.
protected booleanisEqualValue(Object value)
Compares the specified value to the stored value.
booleanisFull()
Is the map currently full, always true.
SetkeySet()
Gets the unmodifiable keySet view of the map.
ObjectlastKey()
Gets the last (and only) key in the map.
MapIteratormapIterator()
Gets an iterator over the map.
intmaxSize()
Gets the maximum size of the map, always 1.
ObjectnextKey(Object key)
Gets the next key after the key specified, always null.
OrderedMapIteratororderedMapIterator()
Obtains an OrderedMapIterator over the map.
ObjectpreviousKey(Object key)
Gets the previous key before the key specified, always null.
Objectput(Object key, Object value)
Puts a key-value mapping into this map where the key must match the existing key.
voidputAll(Map map)
Puts the values from the specified map into this map.
Objectremove(Object key)
Unsupported operation.
ObjectsetValue(Object value)
Sets the value.
intsize()
Gets the size of the map, always 1.
StringtoString()
Gets the map as a String.
Collectionvalues()
Gets the unmodifiable values view of the map.

Constructor Detail

SingletonMap

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

SingletonMap

public SingletonMap(Object key, Object value)
Constructor specifying the key and value.

Parameters: key the key to use value the value to use

SingletonMap

public SingletonMap(KeyValue keyValue)
Constructor specifying the key and value as a KeyValue.

Parameters: keyValue the key value pair to use

SingletonMap

public SingletonMap(Entry mapEntry)
Constructor specifying the key and value as a MapEntry.

Parameters: mapEntry the mapEntry to use

SingletonMap

public SingletonMap(Map 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

clear

public void clear()
Unsupported operation.

clone

public Object clone()
Clones the map without cloning the key or value.

Returns: a shallow clone

containsKey

public boolean containsKey(Object key)
Checks whether the map contains the specified key.

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.

Parameters: value the value to search for

Returns: true if the map contains the key

entrySet

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

Returns: the entrySet view

equals

public boolean equals(Object obj)
Compares this map with another.

Parameters: obj the object to compare to

Returns: true if equal

firstKey

public Object firstKey()
Gets the first (and only) key in the map.

Returns: the key

get

public Object get(Object key)
Gets the value mapped to the key specified.

Parameters: key the key

Returns: the mapped value, null if no match

getKey

public Object getKey()
Gets the key.

Returns: the key

getValue

public Object getValue()
Gets the value.

Returns: the value

hashCode

public int hashCode()
Gets the standard Map hashCode.

Returns: the hash code defined in the Map interface

isEmpty

public boolean isEmpty()
Checks whether the map is currently empty, which it never is.

Returns: false 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

isFull

public boolean isFull()
Is the map currently full, always true.

Returns: true always

keySet

public Set 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.

Returns: the keySet view

lastKey

public Object lastKey()
Gets the last (and only) key in the map.

Returns: the key

mapIterator

public MapIterator 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.

Returns: the map iterator

maxSize

public int maxSize()
Gets the maximum size of the map, always 1.

Returns: 1 always

nextKey

public Object nextKey(Object key)
Gets the next key after the key specified, always null.

Parameters: key the next key

Returns: null always

orderedMapIterator

public OrderedMapIterator orderedMapIterator()
Obtains an OrderedMapIterator over the map.

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

Returns: an ordered map iterator

previousKey

public Object previousKey(Object key)
Gets the previous key before the key specified, always null.

Parameters: key the next key

Returns: null always

put

public Object put(Object key, Object 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.

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 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.

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 Object remove(Object key)
Unsupported operation.

Parameters: key the mapping to remove

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

Throws: UnsupportedOperationException always

setValue

public Object setValue(Object value)
Sets the value.

Parameters: value the new value to set

Returns: the old value

size

public int size()
Gets the size of the map, always 1.

Returns: the size of 1

toString

public String toString()
Gets the map as a String.

Returns: a string version of the map

values

public Collection 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.

Returns: the values view

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