Class ListOrderedMap<K,V>
- Type Parameters:
K- the type of the keys in this mapV- 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>
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:
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Nested Class Summary
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Constructor Summary
ConstructorsModifierConstructorDescriptionConstructs a new emptyListOrderedMapthat decorates aHashMap.protectedListOrderedMap(Map<K, V> map) Constructor that wraps (not copies). -
Method Summary
Modifier and TypeMethodDescriptionasList()Gets an unmodifiable List view of the keys which changes as the map changes.voidclear()Removes all of the mappings from this map.entrySet()Gets a view over the entries in the map.firstKey()Gets the first key in this map by insert order.get(int index) Gets the key at the specified index.getValue(int index) Gets the value at the specified index.intGets the index of the specified key.keyList()Gets a view over the keys in the map as a List.keySet()Gets a view over the keys in the map.lastKey()Gets the last key in this map by insert order.static <K,V> ListOrderedMap <K, V> listOrderedMap(Map<K, V> map) Factory method to create an ordered map.Obtains aMapIteratorover the map.Gets the next key to the one specified using insert order.previousKey(Object key) Gets the previous key to the one specified using insert order.Puts a key-value mapping into the map at the specified index.Associates the specified value with the specified key in this map.voidPuts the values contained in a supplied Map into the Map starting at the specified index.voidCopies all of the mappings from the specified map to this map.remove(int index) Removes the element at the specified index.Remove a key-value mappings.Sets the value at the specified index.toString()Returns the Map as a string.Gets a view over the values in the map as a List.values()Gets a view over the values in the map.Methods inherited from class org.apache.commons.collections4.map.AbstractMapDecorator
containsKey, containsValue, decorated, equals, get, hashCode, isEmpty, sizeMethods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, waitMethods inherited from interface org.apache.commons.collections4.Get
containsKey, containsValue, get, isEmpty, sizeMethods inherited from interface java.util.Map
compute, computeIfAbsent, computeIfPresent, containsKey, containsValue, equals, forEach, get, getOrDefault, hashCode, isEmpty, merge, putIfAbsent, remove, replace, replace, replaceAll, size
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Constructor Details
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ListOrderedMap
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ListOrderedMap
Constructor that wraps (not copies).- Parameters:
map- the map to decorate, must not be null- Throws:
NullPointerException- if map is null
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Method Details
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listOrderedMap
Factory method to create an ordered map.An
ArrayListis used to retain order.- Type Parameters:
K- the key typeV- 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
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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()orkeySet().- Returns:
- The ordered list of keys.
- See Also:
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clear
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entrySet
Gets a view over the entries in the map.The Set will be ordered by object insertion into the map.
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firstKey
Gets the first key in this map by insert order.- Specified by:
firstKeyin interfaceOrderedMap<K,V> - Returns:
- the first key currently in this map
- Throws:
NoSuchElementException- if this map is empty
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get
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
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getValue
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
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indexOf
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keyList
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keySet
Gets a view over the keys in the map.The Collection will be ordered by object insertion into the map.
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lastKey
Gets the last key in this map by insert order.- Specified by:
lastKeyin interfaceOrderedMap<K,V> - Returns:
- the last key currently in this map
- Throws:
NoSuchElementException- if this map is empty
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mapIterator
Description copied from class:AbstractIterableMapObtains aMapIteratorover 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:
mapIteratorin interfaceIterableGet<K,V> - Specified by:
mapIteratorin interfaceOrderedMap<K,V> - Overrides:
mapIteratorin classAbstractIterableMap<K,V> - Returns:
- a map iterator
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nextKey
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:
nextKeyin interfaceOrderedMap<K,V> - Parameters:
key- the key to find previous for- Returns:
- the next key, null if no match or at start
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previousKey
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:
previousKeyin interfaceOrderedMap<K,V> - Parameters:
key- the key to find previous for- Returns:
- the previous key, null if no match or at start
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put
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 insertedkey- the keyvalue- the value- Returns:
- the value previously mapped to the key
- Throws:
IndexOutOfBoundsException- if the index is out of range [0, size]- Since:
- 3.2
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put
Description copied from interface:PutAssociates the specified value with the specified key in this map.Note that the return type is Object, rather than V as in the Map interface. See the class Javadoc for further info.
- Specified by:
putin interfaceMap<K,V> - Specified by:
putin interfacePut<K,V> - Overrides:
putin classAbstractMapDecorator<K,V> - Parameters:
key- key with which the specified value is to be associatedvalue- value to be associated with the specified key- Returns:
- the previous value associated with
key, ornullif there was no mapping forkey. (Anullreturn can also indicate that the map previously associatednullwithkey, if the implementation supportsnullvalues.) - See Also:
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putAll
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]
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putAll
Description copied from interface:PutCopies all of the mappings from the specified map to this map. -
remove
Removes the element at the specified index.- Parameters:
index- the index of the object to remove- Returns:
- the removed value, or
nullif none existed - Throws:
IndexOutOfBoundsException- if the index is invalid
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remove
Description copied from interface:GetRemove a key-value mappings.- Specified by:
removein interfaceGet<K,V> - Specified by:
removein interfaceMap<K,V> - Overrides:
removein classAbstractMapDecorator<K,V> - Parameters:
key- key whose mapping is to be removed from the map- Returns:
- the previous value associated with
key, ornullif there was no mapping forkey. - See Also:
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setValue
Sets the value at the specified index.- Parameters:
index- the index of the value to setvalue- the new value to set- Returns:
- the previous value at that index
- Throws:
IndexOutOfBoundsException- if the index is invalid- Since:
- 3.2
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toString
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valueList
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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()
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