SingletonMap (Apache Commons Collections 4.4 API)

java.lang.Object
- org.apache.commons.collections4.map.SingletonMap<K,V>

Type Parameters:

K - the type of the keys in this map

V - the type of the values in this map

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 succeed 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:

3.1

See Also:

Serialized Form

Nested Class Summary
- Nested classes/interfaces inherited from interface java.util.Map
  Map.Entry<K,V>

Constructor Summary

Constructors
Constructor and Description
`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<? extends K,? extends V> mapEntry)` Constructor specifying the key and value as a `MapEntry`.
`SingletonMap(Map<? extends K,? extends V> map)` Constructor copying elements from another map.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`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 an `OrderedMapIterator` 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

Methods inherited from interface java.util.Map
compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll

- 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<? extends K,? extends V> mapEntry)
```
    Constructor specifying the key and value as a MapEntry.
    
    Parameters:
    
    mapEntry - the mapEntry 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>
    
    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 an OrderedMapIterator over the map.
    A ordered map iterator is an efficient way of iterating over maps in both directions.
    
    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

Class SingletonMap<K,V>

Nested Class Summary

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

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Map

Constructor Detail

SingletonMap

SingletonMap

SingletonMap

SingletonMap

SingletonMap

Method Detail

getKey

getValue

setValue

isFull

maxSize

get

size

isEmpty

containsKey

containsValue

put

putAll

remove

clear

entrySet

keySet

values

mapIterator

firstKey

lastKey

nextKey

previousKey

isEqualKey

isEqualValue

clone

equals

hashCode

toString