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## org.apache.commons.collections.map
Class DefaultedMap

    java.lang.Object
      org.apache.commons.collections.map.AbstractMapDecorator
          org.apache.commons.collections.map.DefaultedMap

All Implemented Interfaces:
  java.io.Serializable, java.util.Map

    public class DefaultedMap

extends AbstractMapDecorator
implements java.util.Map, java.io.Serializable

Decorates another `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 13:33:15 +0100 (Thu, 10 Apr 2008) $
Author:
  Stephen Colebourne, Rafael U.C. Afonso
See Also:
  `LazyMap`, Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map
`java.util.Map.Entry`

Field Summary
`protected java.lang.Object` | `value` The transformer to use if the map does not contain a key

Fields inherited from class org.apache.commons.collections.map.AbstractMapDecorator
`map`

Constructor Summary
`protected` | `DefaultedMap(java.util.Map map, java.lang.Object value)` Constructor that wraps (not copies).
`` | `DefaultedMap(java.lang.Object defaultValue)` Constructs a new empty `DefaultedMap` that decorates a `HashMap`.

Method Summary
`static java.util.Map` | `decorate(java.util.Map map, Factory factory)` Factory method to create a defaulting map.
`static java.util.Map` | `decorate(java.util.Map map, java.lang.Object defaultValue)` Factory method to create a defaulting map.
`static java.util.Map` | `decorate(java.util.Map map, Transformer factory)` Factory method to create a defaulting map.
`java.lang.Object` | `get(java.lang.Object key)`

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, containsKey, containsValue, entrySet, equals, hashCode, isEmpty, keySet, put, putAll, remove, size, values`

Field Detail

### value

    protected final java.lang.Object value

  The transformer to use if the map does not contain a key

Constructor Detail

### DefaultedMap

    public DefaultedMap(java.lang.Object defaultValue)

  Constructs a new empty `DefaultedMap` that decorates a `HashMap`.

  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

    protected DefaultedMap(java.util.Map map,
                           java.lang.Object value)

  Constructor that wraps (not copies).

  Parameters:
    `map` - the map to decorate, must not be null
    `value` - the value to use
  Throws:
    `java.lang.IllegalArgumentException` - if map or transformer is null

Method Detail

### decorate

    public static java.util.Map decorate(java.util.Map map,
                                         java.lang.Object defaultValue)

  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 null
    `defaultValue` - the default value to return when the key is not found
  Throws:
    `java.lang.IllegalArgumentException` - if map is null

### decorate

    public static java.util.Map decorate(java.util.Map map,
                                         Factory factory)

  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 null
    `factory` - the factory to use, must not be null
  Throws:
    `java.lang.IllegalArgumentException` - if map or factory is null

### decorate

    public static java.util.Map decorate(java.util.Map map,
                                         Transformer factory)

  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 null
    `factory` - the factory to use, must not be null
  Throws:
    `java.lang.IllegalArgumentException` - if map or factory is null

### get

    public java.lang.Object get(java.lang.Object key)

  Specified by:
    `get` in interface `java.util.Map`
  Overrides:
    `get` in class `AbstractMapDecorator`

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