Class DefaultedMap
- All Implemented Interfaces:
Serializable
,Map
Map
returning a default value if the map
does not contain the requested key.
When the get(Object)
method is called with a key that does not
exist in the map, this map will return the default value specified in
the constructor/factory. Only the get method is altered, so the
Map.containsKey(Object)
can be used to determine if a key really
is in the map or not.
The defaulted value is not added to the map.
Compare this behaviour with LazyMap
, which does add the value
to the map (via a Transformer).
For instance:
Map map = new DefaultedMap("NULL"); Object obj = map.get("Surname"); // obj == "NULL"After the above code is executed the map is still empty.
Note that DefaultedMap 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.
- Since:
- Commons Collections 3.2
- Version:
- $Revision: 1.7 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
- See Also:
-
Nested Class Summary
-
Field Summary
FieldsModifier and TypeFieldDescriptionprivate static final long
Serialization versionprotected final Object
The transformer to use if the map does not contain a keyFields inherited from class org.apache.commons.collections.map.AbstractMapDecorator
map
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Constructor Summary
ConstructorsModifierConstructorDescriptionDefaultedMap
(Object defaultValue) Constructs a new emptyDefaultedMap
that decorates aHashMap
.protected
DefaultedMap
(Map map, Object value) Constructor that wraps (not copies). -
Method Summary
Modifier and TypeMethodDescriptionstatic Map
Factory method to create a defaulting map.static Map
Factory method to create a defaulting map.static Map
decorate
(Map map, Transformer factory) Factory method to create a defaulting map.private void
Read the map in using a custom routine.private void
Write the map out using a custom routine.Methods inherited from class org.apache.commons.collections.map.AbstractMapDecorator
clear, containsKey, containsValue, entrySet, equals, getMap, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, values
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
Methods inherited from interface java.util.Map
clear, compute, computeIfAbsent, computeIfPresent, containsKey, containsValue, entrySet, equals, forEach, getOrDefault, hashCode, isEmpty, keySet, merge, put, putAll, putIfAbsent, remove, remove, replace, replace, replaceAll, size, values
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Field Details
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serialVersionUID
private static final long serialVersionUIDSerialization version- See Also:
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value
The transformer to use if the map does not contain a key
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Constructor Details
-
DefaultedMap
Constructs a new emptyDefaultedMap
that decorates aHashMap
.The object passed in will be returned by the map whenever an unknown key is requested.
- Parameters:
defaultValue
- the default value to return when the key is not found
-
DefaultedMap
Constructor that wraps (not copies).- Parameters:
map
- the map to decorate, must not be nullvalue
- the value to use- Throws:
IllegalArgumentException
- if map or transformer is null
-
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Method Details
-
decorate
Factory method to create a defaulting map.The value specified is returned when a missing key is found.
- Parameters:
map
- the map to decorate, must not be nulldefaultValue
- the default value to return when the key is not found- Throws:
IllegalArgumentException
- if map is null
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decorate
Factory method to create a defaulting map.The factory specified is called when a missing key is found. The result will be returned as the result of the map get(key) method.
- Parameters:
map
- the map to decorate, must not be nullfactory
- the factory to use, must not be null- Throws:
IllegalArgumentException
- if map or factory is null
-
decorate
Factory method to create a defaulting map.The transformer specified is called when a missing key is found. The key is passed to the transformer as the input, and the result will be returned as the result of the map get(key) method.
- Parameters:
map
- the map to decorate, must not be nullfactory
- the factory to use, must not be null- Throws:
IllegalArgumentException
- if map or factory is null
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writeObject
Write the map out using a custom routine.- Parameters:
out
- the output stream- Throws:
IOException
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readObject
Read the map in using a custom routine.- Parameters:
in
- the input stream- Throws:
IOException
ClassNotFoundException
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get
- Specified by:
get
in interfaceMap
- Overrides:
get
in classAbstractMapDecorator
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