org.apache.commons.collections.map

Class SingletonMap

Implemented Interfaces:
Cloneable, IterableMap, Map, BoundedMap, KeyValue, OrderedMap, Serializable

public class SingletonMap
extends java.lang.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:

Version:
$Revision: 1.1 $ $Date: 2004/04/09 14:46:35 $
Author:
Stephen Colebourne
Since:
Commons Collections 3.1

Constructor Summary

SingletonMap()
Constructor that creates a map of null to null.
SingletonMap(Map map)
Constructor copying elements from another map.
SingletonMap(Map.Entry entry)
Constructor specifying the key and value as a MapEntry.
SingletonMap(Object key, Object value)
Constructor specifying the key and value.
SingletonMap(KeyValue keyValue)
Constructor specifying the key and value as a KeyValue.

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
entrySet()
Gets the entrySet view of the map.
boolean
equals(Object obj)
Compares this map with another.
Object
firstKey()
Gets the first (and only) key in the map.
Object
get(Object key)
Gets the value mapped to the key specified.
Object
getKey()
Gets the key.
Object
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
keySet()
Gets the unmodifiable keySet view of the map.
Object
lastKey()
Gets the last (and only) key in the map.
MapIterator
mapIterator()
Gets an iterator over the map.
int
maxSize()
Gets the maximum size of the map, always 1.
Object
nextKey(Object key)
Gets the next key after the key specified, always null.
OrderedMapIterator
orderedMapIterator()
Obtains an OrderedMapIterator over the map.
Object
previousKey(Object key)
Gets the previous key before the key specified, always null.
Object
put(Object key, Object value)
Puts a key-value mapping into this map where the key must match the existing key.
void
putAll(Map map)
Puts the values from the specified map into this map.
Object
remove(Object key)
Unsupported operation.
Object
setValue(Object value)
Sets the value.
int
size()
Gets the size of the map, always 1.
String
toString()
Gets the map as a String.
Collection
values()
Gets the unmodifiable values view of the map.

Constructor Details

SingletonMap

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

SingletonMap

public SingletonMap(Map map)
Constructor copying elements from another map.
Parameters:
map - the map to copy, must be size 1

SingletonMap

public SingletonMap(Map.Entry entry)
Constructor specifying the key and value as a MapEntry.
Parameters:

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

Method Details

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()
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.
Specified by:
firstKey in interface OrderedMap
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.
Specified by:
getKey in interface KeyValue
Returns:
the key

getValue

public Object getValue()
Gets the value.
Specified by:
getValue in interface KeyValue
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.
Specified by:
isFull in interface BoundedMap
Returns:
true always

keySet

public Set keySet()
Returns:
the keySet view

lastKey

public Object lastKey()
Gets the last (and only) key in the map.
Specified by:
lastKey in interface OrderedMap
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.

Specified by:
mapIterator in interface IterableMap
Returns:
the map iterator

maxSize

public int maxSize()
Gets the maximum size of the map, always 1.
Specified by:
maxSize in interface BoundedMap
Returns:
1 always

nextKey

public Object nextKey(Object key)
Gets the next key after the key specified, always null.
Specified by:
nextKey in interface OrderedMap
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.

Specified by:
orderedMapIterator in interface OrderedMap
Returns:
an ordered map iterator

previousKey

public Object previousKey(Object key)
Gets the previous key before the key specified, always null.
Specified by:
previousKey in interface OrderedMap
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

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

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

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()
Returns:
the values view

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