Package org.apache.commons.collections4.map

This package contains implementations of the Map, IterableMap, OrderedMap and SortedMap interfaces. A Map provides a lookup from a key to a value. A number of implementations also support the new MapIterator interface that enables simple iteration of map keys and values.

The following implementations are provided:

• CaseInsensitiveMap - map that compares keys in a case insensitive way
• CompositeMap - map that combines multiple maps into a single view
• HashedMap - general purpose HashMap replacement supporting MapIterator
• Flat3Map - designed for good performance at size 3 or less
• LinkedMap - a hash map that maintains insertion order, supporting OrderedMapIterator
• LRUMap - a hash map that maintains a maximum size by removing the least recently used entries
• MultiKeyMap - map that provides special methods for using more than one key to access the value
• ReferenceMap - allows the garbage collector to collect keys and values using equals() for comparison
• ReferenceIdentityMap - allows the garbage collector to collect keys and values using == for comparison
• SingletonMap - a fully featured map to hold one key-value pair
• StaticBucketMap - internally synchronized and designed for thread-contentious environments

The following decorators are provided:

• Unmodifiable - ensures the collection cannot be altered
• Predicated - ensures that only elements that are valid according to a predicate can be added
• Transformed - transforms each element added
• FixedSize - ensures that the size of the map cannot change
• Defaulted - provides default values for non-existing keys
• Lazy - creates objects in the map on demand
• ListOrdered - ensures that insertion order is retained

Interface Summary

Interface	Description
CompositeMap.MapMutator<K,V>	This interface allows definition for all of the indeterminate mutators in a CompositeMap, as well as providing a hook for callbacks on key collisions.
PassiveExpiringMap.ExpirationPolicy<K,V>	A policy to determine the expiration time for key-value entries.

Class Summary

Class	Description
AbstractHashedMap<K,V>	An abstract implementation of a hash-based map which provides numerous points for subclasses to override.
AbstractIterableMap<K,V>	Provide a basic IterableMap implementation.
AbstractLinkedMap<K,V>	An abstract implementation of a hash-based map that links entries to create an ordered map and which provides numerous points for subclasses to override.
AbstractMapDecorator<K,V>	Provides a base decorator that enables additional functionality to be added to a Map via decoration.
AbstractOrderedMapDecorator<K,V>	Provides a base decorator that enables additional functionality to be added to an OrderedMap via decoration.
AbstractReferenceMap<K,V>	An abstract implementation of a hash-based map that allows the entries to be removed by the garbage collector.
AbstractSortedMapDecorator<K,V>	Provides a base decorator that enables additional functionality to be added to a Map via decoration.
CaseInsensitiveMap<K,V>	A case-insensitive Map.
CompositeMap<K,V>	Decorates a map of other maps to provide a single unified view.
DefaultedMap<K,V>	Decorates another Map returning a default value if the map does not contain the requested key.
EntrySetToMapIteratorAdapter<K,V>	Adapts a Map entrySet to the MapIterator interface.
FixedSizeMap<K,V>	Decorates another Map to fix the size, preventing add/remove.
FixedSizeSortedMap<K,V>	Decorates another SortedMap to fix the size blocking add/remove.
Flat3Map<K,V>	A Map implementation that stores data in simple fields until the size is greater than 3.
HashedMap<K,V>	A Map implementation that is a general purpose alternative to HashMap.
LazyMap<K,V>	Decorates another Map to create objects in the map on demand.
LazySortedMap<K,V>	Decorates another SortedMap to create objects in the map on demand.
LinkedMap<K,V>	A Map implementation that maintains the order of the entries.
ListOrderedMap<K,V>	Decorates a Map to ensure that the order of addition is retained using a List to maintain order.
LRUMap<K,V>	A Map implementation with a fixed maximum size which removes the least recently used entry if an entry is added when full.
MultiKeyMap<K,V>	A Map implementation that uses multiple keys to map the value.
MultiValueMap<K,V>	Deprecated. since 4.1, use MultiValuedMap instead
PassiveExpiringMap<K,V>	Decorates a Map to evict expired entries once their expiration time has been reached.
PassiveExpiringMap.ConstantTimeToLiveExpirationPolicy<K,V>	A ExpirationPolicy that returns a expiration time that is a constant about of time in the future from the current time.
PredicatedMap<K,V>	Decorates another Map to validate that additions match a specified predicate.
PredicatedSortedMap<K,V>	Decorates another SortedMap to validate that additions match a specified predicate.
ReferenceIdentityMap<K,V>	A Map implementation that allows mappings to be removed by the garbage collector and matches keys and values based on == not equals().
ReferenceMap<K,V>	A Map implementation that allows mappings to be removed by the garbage collector.
SingletonMap<K,V>	A Map implementation that holds a single item and is fixed size.
StaticBucketMap<K,V>	A StaticBucketMap is an efficient, thread-safe implementation of java.util.Map that performs well in in a highly thread-contentious environment.
TransformedMap<K,V>	Decorates another Map to transform objects that are added.
TransformedSortedMap<K,V>	Decorates another SortedMap to transform objects that are added.
UnmodifiableEntrySet<K,V>	Decorates a map entry Set to ensure it can't be altered.
UnmodifiableMap<K,V>	Decorates another Map to ensure it can't be altered.
UnmodifiableOrderedMap<K,V>	Decorates another OrderedMap to ensure it can't be altered.
UnmodifiableSortedMap<K,V>	Decorates another SortedMap to ensure it can't be altered.

Enum Summary

Enum	Description
AbstractReferenceMap.ReferenceStrength	Reference type enum.