Package org.apache.commons.collections.map

Class SingletonMap

  • All Implemented Interfaces:
    java.io.Serializable, java.lang.Cloneable, java.util.Map, BoundedMap, IterableMap, KeyValue, OrderedMap
    public class SingletonMap
extends java.lang.Object
implements OrderedMap, BoundedMap, KeyValue, java.io.Serializable, java.lang.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
    See Also:
    Serialized Form

    • Nested Class Summary

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

        java.util.Map.Entry<K extends java.lang.Object,​V extends java.lang.Object>

    • Constructor Summary

      Constructors 
      Constructor Description
      SingletonMap()
      Constructor that creates a map of null to null.
      SingletonMap​(java.lang.Object key, java.lang.Object value)
      Constructor specifying the key and value.
      SingletonMap​(java.util.Map map)
      Constructor copying elements from another map.
      SingletonMap​(java.util.Map.Entry mapEntry)
      Constructor specifying the key and value as a MapEntry.
      SingletonMap​(KeyValue keyValue)
      Constructor specifying the key and value as a KeyValue.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void clear()
      Unsupported operation.
      java.lang.Object clone()
      Clones the map without cloning the key or value.
      boolean containsKey​(java.lang.Object key)
      Checks whether the map contains the specified key.
      boolean containsValue​(java.lang.Object value)
      Checks whether the map contains the specified value.
      java.util.Set entrySet()
      Gets the entrySet view of the map.
      boolean equals​(java.lang.Object obj)
      Compares this map with another.
      java.lang.Object firstKey()
      Gets the first (and only) key in the map.
      java.lang.Object get​(java.lang.Object key)
      Gets the value mapped to the key specified.
      java.lang.Object getKey()
      Gets the key.
      java.lang.Object getValue()
      Gets the value.
      int hashCode()
      Gets the standard Map hashCode.
      boolean isEmpty()
      Checks whether the map is currently empty, which it never is.
      boolean isFull()
      Is the map currently full, always true.
      java.util.Set keySet()
      Gets the unmodifiable keySet view of the map.
      java.lang.Object lastKey()
      Gets the last (and only) key in the map.
      MapIterator mapIterator()
      Gets an iterator over the map.
      int maxSize()
      Gets the maximum size of the map, always 1.
      java.lang.Object nextKey​(java.lang.Object key)
      Gets the next key after the key specified, always null.
      OrderedMapIterator orderedMapIterator()
      Obtains an OrderedMapIterator over the map.
      java.lang.Object previousKey​(java.lang.Object key)
      Gets the previous key before the key specified, always null.
      java.lang.Object put​(java.lang.Object key, java.lang.Object value)
      Puts a key-value mapping into this map where the key must match the existing key.
      void putAll​(java.util.Map map)
      Puts the values from the specified map into this map.
      java.lang.Object remove​(java.lang.Object key)
      Unsupported operation.
      java.lang.Object setValue​(java.lang.Object value)
      Sets the value.
      int size()
      Gets the size of the map, always 1.
      java.lang.String toString()
      Gets the map as a String.
      java.util.Collection values()
      Gets the unmodifiable values view of the map.

      • Methods inherited from class java.lang.Object

        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​(java.lang.Object key,
                    java.lang.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​(java.util.Map.Entry mapEntry)
        Constructor specifying the key and value as a MapEntry.
        Parameters:
        mapEntry - the mapEntry to use

      • SingletonMap

        public SingletonMap​(java.util.Map map)
        Constructor copying elements from another map.
        Parameters:
        map - the map to copy, must be size 1
        Throws:
        java.lang.NullPointerException - if the map is null
        java.lang.IllegalArgumentException - if the size is not 1

    • Method Detail

      • getKey

        public java.lang.Object getKey()
        Gets the key.
        Specified by:
        getKey in interface KeyValue
        Returns:
        the key

      • getValue

        public java.lang.Object getValue()
        Gets the value.
        Specified by:
        getValue in interface KeyValue
        Returns:
        the value

      • setValue

        public java.lang.Object setValue​(java.lang.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 java.lang.Object get​(java.lang.Object key)
        Gets the value mapped to the key specified.
        Specified by:
        get in interface java.util.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 java.util.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 java.util.Map
        Returns:
        false always

      • containsKey

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

      • containsValue

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

      • put

        public java.lang.Object put​(java.lang.Object key,
                            java.lang.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 java.util.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:
        java.lang.IllegalArgumentException - if the key does not match

      • putAll

        public void putAll​(java.util.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 java.util.Map
        Parameters:
        map - the map to add, must be size 0 or 1, and the key must match
        Throws:
        java.lang.NullPointerException - if the map is null
        java.lang.IllegalArgumentException - if the key does not match

      • remove

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

      • clear

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

      • entrySet

        public java.util.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 java.util.Map
        Returns:
        the entrySet view

      • keySet

        public java.util.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 java.util.Map
        Returns:
        the keySet view

      • values

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

      • lastKey

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

      • nextKey

        public java.lang.Object nextKey​(java.lang.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 java.lang.Object previousKey​(java.lang.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

      • clone

        public java.lang.Object clone()
        Clones the map without cloning the key or value.
        Returns:
        a shallow clone

      • equals

        public boolean equals​(java.lang.Object obj)
        Compares this map with another.
        Specified by:
        equals in interface java.util.Map
        Overrides:
        equals in class java.lang.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 java.util.Map
        Overrides:
        hashCode in class java.lang.Object
        Returns:
        the hash code defined in the Map interface

      • toString

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