Package org.apache.commons.collections4.map

Class ListOrderedMap<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, Map<K,​V>, Get<K,​V>, IterableGet<K,​V>, IterableMap<K,​V>, OrderedMap<K,​V>, Put<K,​V>
    public class ListOrderedMap<K,​V>
extends AbstractMapDecorator<K,​V>
implements OrderedMap<K,​V>, Serializable
    Decorates a Map to ensure that the order of addition is retained using a List to maintain order.

    The order will be used via the iterators and toArray methods on the views. The order is also returned by the MapIterator. The orderedMapIterator() method accesses an iterator that can iterate both forwards and backwards through the map. In addition, non-interface methods are provided to access the map by index.

    If an object is added to the Map for a second time, it will remain in the original position in the iteration.

    Note that ListOrderedMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using Collections.synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

    Note that ListOrderedMap doesn't work with IdentityHashMap, CaseInsensitiveMap, or similar maps that violate the general contract of Map. The ListOrderedMap (or, more precisely, the underlying List) is relying on equals(). This is fine, as long as the decorated Map is also based on equals(), and hashCode(), which IdentityHashMap, and CaseInsensitiveMap don't: The former uses ==, and the latter uses equals() on a lower-cased key.

    This class is Serializable starting with Commons Collections 3.1.

    Since:
    3.0
    See Also:
    Serialized Form

    • Constructor Detail

      • ListOrderedMap

        public ListOrderedMap()
        Constructs a new empty ListOrderedMap that decorates a HashMap.
        Since:
        3.1

      • ListOrderedMap

        protected ListOrderedMap​(Map<K,​V> map)
        Constructor that wraps (not copies).
        Parameters:
        map - the map to decorate, must not be null
        Throws:
        NullPointerException - if map is null

    • Method Detail

      • listOrderedMap

        public static <K,​V> ListOrderedMap<K,​V> listOrderedMap​(Map<K,​V> map)
        Factory method to create an ordered map.

        An ArrayList is used to retain order.

        Type Parameters:
        K - the key type
        V - the value type
        Parameters:
        map - the map to decorate, must not be null
        Returns:
        a new list ordered map
        Throws:
        NullPointerException - if map is null
        Since:
        4.0

      • mapIterator

        public OrderedMapIterator<K,​V> mapIterator()
        Description copied from class: AbstractIterableMap
        Obtains a MapIterator over the map.

        A map iterator is an efficient way of iterating over maps. There is no need to access the entry set or use Map Entry objects. 

         IterableMap<String,Integer> map = new HashedMap<String,Integer>();
 MapIterator<String,Integer> it = map.mapIterator();
 while (it.hasNext()) {
   String key = it.next();
   Integer value = it.getValue();
   it.setValue(value + 1);
 }
        Specified by:
        mapIterator in interface IterableGet<K,​V>
        Specified by:
        mapIterator in interface OrderedMap<K,​V>
        Overrides:
        mapIterator in class AbstractIterableMap<K,​V>
        Returns:
        a map iterator

      • firstKey

        public K firstKey()
        Gets the first key in this map by insert order.
        Specified by:
        firstKey in interface OrderedMap<K,​V>
        Returns:
        the first key currently in this map
        Throws:
        NoSuchElementException - if this map is empty

      • lastKey

        public K lastKey()
        Gets the last key in this map by insert order.
        Specified by:
        lastKey in interface OrderedMap<K,​V>
        Returns:
        the last key currently in this map
        Throws:
        NoSuchElementException - if this map is empty

      • nextKey

        public K nextKey​(Object key)
        Gets the next key to the one specified using insert order. This method performs a list search to find the key and is O(n).
        Specified by:
        nextKey in interface OrderedMap<K,​V>
        Parameters:
        key - the key to find previous for
        Returns:
        the next key, null if no match or at start

      • previousKey

        public K previousKey​(Object key)
        Gets the previous key to the one specified using insert order. This method performs a list search to find the key and is O(n).
        Specified by:
        previousKey in interface OrderedMap<K,​V>
        Parameters:
        key - the key to find previous for
        Returns:
        the previous key, null if no match or at start

      • put

        public V put​(K key,
             V value)
        Description copied from interface: Put
        Note that the return type is Object, rather than V as in the Map interface. See the class Javadoc for further info.
        Specified by:
        put in interface Map<K,​V>
        Specified by:
        put in interface Put<K,​V>
        Overrides:
        put in class AbstractMapDecorator<K,​V>
        Parameters:
        key - key with which the specified value is to be associated
        value - value to be associated with the specified key
        Returns:
        the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key, if the implementation supports null values.)
        See Also:
        Map.put(Object, Object)

      • putAll

        public void putAll​(int index,
                   Map<? extends K,​? extends V> map)
        Puts the values contained in a supplied Map into the Map starting at the specified index.
        Parameters:
        index - the index in the Map to start at.
        map - the Map containing the entries to be added.
        Throws:
        IndexOutOfBoundsException - if the index is out of range [0, size]

      • remove

        public V remove​(Object key)
        Specified by:
        remove in interface Get<K,​V>
        Specified by:
        remove in interface Map<K,​V>
        Overrides:
        remove in class AbstractMapDecorator<K,​V>
        Parameters:
        key - key whose mapping is to be removed from the map
        Returns:
        the previous value associated with key, or null if there was no mapping for key.
        See Also:
        Map.remove(Object)

      • keySet

        public Set<K> keySet()
        Gets a view over the keys in the map.

        The Collection will be ordered by object insertion into the map.

        Specified by:
        keySet in interface Get<K,​V>
        Specified by:
        keySet in interface Map<K,​V>
        Overrides:
        keySet in class AbstractMapDecorator<K,​V>
        Returns:
        the fully modifiable collection view over the keys
        See Also:
        keyList()

      • keyList

        public List<K> keyList()
        Gets a view over the keys in the map as a List.

        The List will be ordered by object insertion into the map. The List is unmodifiable.

        Returns:
        the unmodifiable list view over the keys
        Since:
        3.2
        See Also:
        keySet()

      • values

        public Collection<V> values()
        Gets a view over the values in the map.

        The Collection will be ordered by object insertion into the map.

        From Commons Collections 3.2, this Collection can be cast to a list, see valueList()

        Specified by:
        values in interface Get<K,​V>
        Specified by:
        values in interface Map<K,​V>
        Overrides:
        values in class AbstractMapDecorator<K,​V>
        Returns:
        the fully modifiable collection view over the values
        See Also:
        valueList()

      • valueList

        public List<V> valueList()
        Gets a view over the values in the map as a List.

        The List will be ordered by object insertion into the map. The List supports remove and set, but does not support add.

        Returns:
        the partially modifiable list view over the values
        Since:
        3.2
        See Also:
        values()

      • get

        public K get​(int index)
        Gets the key at the specified index.
        Parameters:
        index - the index to retrieve
        Returns:
        the key at the specified index
        Throws:
        IndexOutOfBoundsException - if the index is invalid

      • getValue

        public V getValue​(int index)
        Gets the value at the specified index.
        Parameters:
        index - the index to retrieve
        Returns:
        the key at the specified index
        Throws:
        IndexOutOfBoundsException - if the index is invalid

      • indexOf

        public int indexOf​(Object key)
        Gets the index of the specified key.
        Parameters:
        key - the key to find the index of
        Returns:
        the index, or -1 if not found

      • setValue

        public V setValue​(int index,
                  V value)
        Sets the value at the specified index.
        Parameters:
        index - the index of the value to set
        value - the new value to set
        Returns:
        the previous value at that index
        Throws:
        IndexOutOfBoundsException - if the index is invalid
        Since:
        3.2

      • put

        public V put​(int index,
             K key,
             V value)
        Puts a key-value mapping into the map at the specified index.

        If the map already contains the key, then the original mapping is removed and the new mapping added at the specified index. The remove may change the effect of the index. The index is always calculated relative to the original state of the map.

        Thus the steps are: (1) remove the existing key-value mapping, then (2) insert the new key-value mapping at the position it would have been inserted had the remove not occurred.

        Parameters:
        index - the index at which the mapping should be inserted
        key - the key
        value - the value
        Returns:
        the value previously mapped to the key
        Throws:
        IndexOutOfBoundsException - if the index is out of range [0, size]
        Since:
        3.2

      • remove

        public V remove​(int index)
        Removes the element at the specified index.
        Parameters:
        index - the index of the object to remove
        Returns:
        the removed value, or null if none existed
        Throws:
        IndexOutOfBoundsException - if the index is invalid

      • asList

        public List<K> asList()
        Gets an unmodifiable List view of the keys which changes as the map changes.

        The returned list is unmodifiable because changes to the values of the list (using ListIterator.set(Object)) will effectively remove the value from the list and reinsert that value at the end of the list, which is an unexpected side effect of changing the value of a list. This occurs because changing the key, changes when the mapping is added to the map and thus where it appears in the list.

        An alternative to this method is to use the better named keyList() or keySet().

        Returns:
        The ordered list of keys.
        See Also:
        keyList(), keySet()