public class

SingletonMap

extends Object
implements Serializable Cloneable BoundedMap KeyValue OrderedMap
java.lang.Object
   ↳ org.apache.commons.collections.map.SingletonMap

Class Overview

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)

Summary

Public Constructors
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.
Public Methods
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.
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.
Protected Methods
boolean isEqualKey(Object key)
Compares the specified key to the stored key.
boolean isEqualValue(Object value)
Compares the specified value to the stored value.
[Expand]
Inherited Methods
From class java.lang.Object
From interface java.util.Map
From interface org.apache.commons.collections.BoundedMap
From interface org.apache.commons.collections.IterableMap
From interface org.apache.commons.collections.KeyValue
From interface org.apache.commons.collections.OrderedMap

Public Constructors

public SingletonMap ()

Constructor that creates a map of null to null.

public SingletonMap (Object key, Object value)

Constructor specifying the key and value.

Parameters
key the key to use
value the value to use

public SingletonMap (KeyValue keyValue)

Constructor specifying the key and value as a KeyValue.

Parameters
keyValue the key value pair to use

public SingletonMap (Entry mapEntry)

Constructor specifying the key and value as a MapEntry.

Parameters
mapEntry the mapEntry to use

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

Public Methods

public void clear ()

Unsupported operation.

public Object clone ()

Clones the map without cloning the key or value.

Returns
  • a shallow clone

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

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

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

public boolean equals (Object obj)

Compares this map with another.

Parameters
obj the object to compare to
Returns
  • true if equal

public Object firstKey ()

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

Returns
  • the key

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

public Object getKey ()

Gets the key.

Returns
  • the key

public Object getValue ()

Gets the value.

Returns
  • the value

public int hashCode ()

Gets the standard Map hashCode.

Returns
  • the hash code defined in the Map interface

public boolean isEmpty ()

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

Returns
  • false always

public boolean isFull ()

Is the map currently full, always true.

Returns
  • true always

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

public Object lastKey ()

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

Returns
  • the key

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

public int maxSize ()

Gets the maximum size of the map, always 1.

Returns
  • 1 always

public Object nextKey (Object key)

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

Parameters
key the next key
Returns
  • null always

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

public Object previousKey (Object key)

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

Parameters
key the next key
Returns
  • null always

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

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

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

public Object setValue (Object value)

Sets the value.

Parameters
value the new value to set
Returns
  • the old value

public int size ()

Gets the size of the map, always 1.

Returns
  • the size of 1

public String toString ()

Gets the map as a String.

Returns
  • a string version of the map

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

Protected Methods

protected boolean isEqualKey (Object key)

Compares the specified key to the stored key.

Parameters
key the key to compare
Returns
  • true if equal

protected boolean isEqualValue (Object value)

Compares the specified value to the stored value.

Parameters
value the value to compare
Returns
  • true if equal