Package org.apache.commons.collections.map

Class SingletonMap

java.lang.Object
org.apache.commons.collections.map.SingletonMap
All Implemented Interfaces:
Serializable, Cloneable, Map, BoundedMap, IterableMap, KeyValue, OrderedMap
public class SingletonMap extends 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:

  • normal Map methods and views
  • the MapIterator, see mapIterator()
  • the KeyValue interface (just cast - no object creation)
Since:
Commons Collections 3.1
Version:
$Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
Author:
Stephen Colebourne
See Also:

  • Constructor Details

    • SingletonMap

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

    • 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

    • SingletonMap

      public SingletonMap(Map.Entry mapEntry)
      Constructor specifying the key and value as a MapEntry.
      Parameters:
      mapEntry - the mapEntry to use

    • SingletonMap

      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

  • Method Details

    • 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

    • setValue

      public Object setValue(Object 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
      Returns:
      true always

    • maxSize

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

    • get

      public Object get(Object key)
      Gets the value mapped to the key specified.
      Specified by:
      get in interface Map
      Parameters:
      key - the key
      Returns:
      the mapped value, null if no match

    • size

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

    • isEmpty

      public boolean isEmpty()
      Checks whether the map is currently empty, which it never is.
      Specified by:
      isEmpty in interface Map
      Returns:
      false always

    • containsKey

      public boolean containsKey(Object key)
      Checks whether the map contains the specified key.
      Specified by:
      containsKey in interface Map
      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.
      Specified by:
      containsValue in interface Map
      Parameters:
      value - the value to search for
      Returns:
      true if the map contains the key

    • 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.

      Specified by:
      put in interface Map
      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

    • 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.

      Specified by:
      putAll in interface Map
      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

    • remove

      public Object remove(Object key)
      Unsupported operation.
      Specified by:
      remove in interface Map
      Parameters:
      key - the mapping to remove
      Returns:
      the value mapped to the removed key, null if key not in map
      Throws:
      UnsupportedOperationException - always

    • clear

      public void clear()
      Unsupported operation.
      Specified by:
      clear in interface Map

    • entrySet

      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().
      Specified by:
      entrySet in interface Map
      Returns:
      the entrySet view

    • keySet

      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().
      Specified by:
      keySet in interface Map
      Returns:
      the keySet view

    • values

      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().
      Specified by:
      values in interface Map
      Returns:
      the values view

    • 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

    • 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

    • firstKey

      public Object firstKey()
      Gets the first (and only) key in the map.
      Specified by:
      firstKey in interface OrderedMap
      Returns:
      the key

    • lastKey

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

    • 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

    • 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

    • 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 Object 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
      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
      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