org.apache.commons.collections4.map
Class SingletonMap<K,V>

java.lang.Object
  extended by org.apache.commons.collections4.map.SingletonMap<K,V>
All Implemented Interfaces:
Serializable, Cloneable, Map<K,V>, BoundedMap<K,V>, Get<K,V>, IterableGet<K,V>, IterableMap<K,V>, KeyValue<K,V>, OrderedMap<K,V>, Put<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:

Since:
3.1
Version:
$Id: SingletonMap.java 1477799 2013-04-30 19:56:11Z tn $
See Also:
Serialized Form

Nested Class Summary
 
Nested classes/interfaces inherited from interface java.util.Map
Map.Entry<K,V>
 
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> mapEntry)
          Constructor specifying the key and value as a MapEntry.
SingletonMap(Map<K,V> map)
          Constructor copying elements from another map.
 
Method Summary
 void clear()
          Unsupported operation.
 SingletonMap<K,V> 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.
 OrderedMapIterator<K,V> mapIterator()
          Obtains a MapIterator 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.
 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> mapEntry)
Constructor specifying the key and value as a MapEntry.

Parameters:
mapEntry - the mapEntry to use

SingletonMap

public SingletonMap(Map<K,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>
Specified by:
get in interface Get<K,V>
Parameters:
key - the key
Returns:
the mapped value, null if no match
See Also:
Map.get(Object)

size

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

Specified by:
size in interface Map<K,V>
Specified by:
size in interface Get<K,V>
Returns:
the size of 1
See Also:
Map.size()

isEmpty

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

Specified by:
isEmpty in interface Map<K,V>
Specified by:
isEmpty in interface Get<K,V>
Returns:
false always
See Also:
Map.isEmpty()

containsKey

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

Specified by:
containsKey in interface Map<K,V>
Specified by:
containsKey in interface Get<K,V>
Parameters:
key - the key to search for
Returns:
true if the map contains the key
See Also:
Map.containsKey(Object)

containsValue

public boolean containsValue(Object value)
Checks whether the map contains the specified value.

Specified by:
containsValue in interface Map<K,V>
Specified by:
containsValue in interface Get<K,V>
Parameters:
value - the value to search for
Returns:
true if the map contains the key
See Also:
Map.containsValue(Object)

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>
Specified by:
put in interface Put<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
See Also:
Map.put(Object, Object)

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>
Specified by:
putAll in interface Put<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
See Also:
Map.putAll(Map)

remove

public V remove(Object key)
Unsupported operation.

Specified by:
remove in interface Map<K,V>
Specified by:
remove in interface Get<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
See Also:
Map.remove(Object)

clear

public void clear()
Unsupported operation.

Specified by:
clear in interface Map<K,V>
Specified by:
clear in interface Put<K,V>
See Also:
Map.clear()

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>
Specified by:
entrySet in interface Get<K,V>
Returns:
the entrySet view
See Also:
Map.entrySet()

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>
Specified by:
keySet in interface Get<K,V>
Returns:
the keySet view
See Also:
Map.keySet()

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>
Specified by:
values in interface Get<K,V>
Returns:
the values view
See Also:
Map.values()

mapIterator

public OrderedMapIterator<K,V> mapIterator()
Obtains a MapIterator over the map.

A map iterator is an efficient way of iterating over maps. There is no need to access the entry set or use Map Entry objects.

 IterableMap map = new HashedMap();
 MapIterator it = map.mapIterator();
 while (it.hasNext()) {
   String key = it.next();
   Integer value = it.getValue();
   it.setValue(value + 1);
 }
 

Specified by:
mapIterator in interface IterableGet<K,V>
Specified by:
mapIterator in interface OrderedMap<K,V>
Returns:
a 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 SingletonMap<K,V> 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


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