Package org.apache.commons.collections4.map

Class 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:
    java.io.Serializable, java.lang.Cloneable, java.util.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 java.lang.Object
implements OrderedMap<K,​V>, BoundedMap<K,​V>, KeyValue<K,​V>, 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 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

        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.util.Map.Entry<? extends K,​? extends V> mapEntry)
      Constructor specifying the key and value as a MapEntry.
      SingletonMap​(java.util.Map<? extends K,​? extends V> map)
      Constructor copying elements from another map.
      SingletonMap​(K key, V value)
      Constructor specifying the key and value.
      SingletonMap​(KeyValue<K,​V> 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.
      SingletonMap<K,​V> 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<java.util.Map.Entry<K,​V>> entrySet()
      Gets the entrySet view of the map.
      boolean equals​(java.lang.Object obj)
      Compares this map with another.
      K firstKey()
      Gets the first (and only) key in the map.
      V get​(java.lang.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.
      boolean isFull()
      Is the map currently full, always true.
      java.util.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​(java.util.Map<? extends K,​? extends V> map)
      Puts the values from the specified map into this map.
      V remove​(java.lang.Object key)
      Unsupported operation.
      V setValue​(V 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<V> 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​(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​(java.util.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​(java.util.Map<? extends K,​? extends V> 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 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​(java.lang.Object key)
        Gets the value mapped to the key specified.
        Specified by:
        get in interface Get<K,​V>
        Specified by:
        get in interface java.util.Map<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 Get<K,​V>
        Specified by:
        size in interface java.util.Map<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 Get<K,​V>
        Specified by:
        isEmpty in interface java.util.Map<K,​V>
        Returns:
        false always
        See Also:
        Map.isEmpty()

      • containsKey

        public boolean containsKey​(java.lang.Object key)
        Checks whether the map contains the specified key.
        Specified by:
        containsKey in interface Get<K,​V>
        Specified by:
        containsKey in interface java.util.Map<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​(java.lang.Object value)
        Checks whether the map contains the specified value.
        Specified by:
        containsValue in interface Get<K,​V>
        Specified by:
        containsValue in interface java.util.Map<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 java.util.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:
        java.lang.IllegalArgumentException - if the key does not match
        See Also:
        Map.put(Object, Object)

      • putAll

        public void putAll​(java.util.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 java.util.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:
        java.lang.NullPointerException - if the map is null
        java.lang.IllegalArgumentException - if the key does not match
        See Also:
        Map.putAll(Map)

      • remove

        public V remove​(java.lang.Object key)
        Unsupported operation.
        Specified by:
        remove in interface Get<K,​V>
        Specified by:
        remove in interface java.util.Map<K,​V>
        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
        See Also:
        Map.remove(Object)

      • clear

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

      • entrySet

        public java.util.Set<java.util.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 java.util.Map<K,​V>
        Returns:
        the entrySet view
        See Also:
        Map.entrySet()

      • keySet

        public java.util.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 java.util.Map<K,​V>
        Returns:
        the keySet view
        See Also:
        Map.keySet()

      • values

        public java.util.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 java.util.Map<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

      • clone

        public SingletonMap<K,​V> 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<K,​V>
        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<K,​V>
        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