Class 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:
    Serialized Form
    • Constructor Detail

      • 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 Detail

      • 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