Package org.apache.commons.collections4.map

Class SingletonMap<K,V>

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:

  • Constructor Details

    • 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 Details

    • clear

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

    • clone

      public SingletonMap<K,V> clone()
      Clones the map without cloning the key or value.
      Overrides:
      clone in class Object
      Returns:
      a shallow clone

    • containsKey

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

    • containsValue

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

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

    • 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

    • firstKey

      public K firstKey()
      Gets the first (and only) key in the map.
      Specified by:
      firstKey in interface OrderedMap<K,V>
      Returns:
      the key

    • get

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

    • 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

    • 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

    • isEmpty

      public boolean isEmpty()
      Checks whether the map is currently empty, which it never is.
      Specified by:
      isEmpty in interface Get<K,V>
      Specified by:
      isEmpty in interface Map<K,V>
      Returns:
      false always
      See Also:

    • 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<K,V>
      Returns:
      true always

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

    • lastKey

      public K lastKey()
      Gets the last (and only) key in the map.
      Specified by:
      lastKey in interface OrderedMap<K,V>
      Returns:
      the key

    • mapIterator

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

      An 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

    • maxSize

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

    • 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

    • 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:

    • 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:

    • remove

      public V remove(Object key)
      Unsupported operation.
      Specified by:
      remove in interface Get<K,V>
      Specified by:
      remove in interface Map<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:

    • setValue

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

    • toString

      public String toString()
      Gets the map as a String.
      Overrides:
      toString in class Object
      Returns:
      a string version of the map

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