## Package org.apache.commons.collections.map

This package contains implementations of the `Map`, `IterableMap`, `OrderedMap` and `SortedMap` interfaces.

See:
Description

Interface Summary
CompositeMap.MapMutator: This interface allows definition for all of the indeterminate mutators in a CompositeMap, as well as providing a hook for callbacks on key collisions.

Class Summary
AbstractHashedMap: An abstract implementation of a hash-based map which provides numerous points for subclasses to override.
AbstractHashedMap.EntrySet: EntrySet implementation.
AbstractHashedMap.EntrySetIterator: EntrySet iterator.
AbstractHashedMap.HashEntry: HashEntry used to store the data.
AbstractHashedMap.HashIterator: Base Iterator
AbstractHashedMap.HashMapIterator: MapIterator implementation.
AbstractHashedMap.KeySet: KeySet implementation.
AbstractHashedMap.KeySetIterator: KeySet iterator.
AbstractHashedMap.Values: Values implementation.
AbstractHashedMap.ValuesIterator: Values iterator.
AbstractLinkedMap: 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.
AbstractLinkedMap.EntrySetIterator: EntrySet iterator.
AbstractLinkedMap.KeySetIterator: KeySet iterator.
AbstractLinkedMap.LinkEntry: LinkEntry that stores the data.
AbstractLinkedMap.LinkIterator: Base Iterator that iterates in link order.
AbstractLinkedMap.LinkMapIterator: MapIterator implementation.
AbstractLinkedMap.ValuesIterator: Values iterator.
AbstractMapDecorator: Provides a base decorator that enables additional functionality to be added to a Map via decoration.
AbstractOrderedMapDecorator: Provides a base decorator that enables additional functionality to be added to an OrderedMap via decoration.
AbstractReferenceMap: An abstract implementation of a hash-based map that allows the entries to be removed by the garbage collector.
AbstractReferenceMap.ReferenceEntry: A MapEntry implementation for the map.
AbstractSortedMapDecorator: Provides a base decorator that enables additional functionality to be added to a Map via decoration.
CaseInsensitiveMap: A case-insensitive `Map`.
CompositeMap: Decorates a map of other maps to provide a single unified view.
DefaultedMap: Decorates another `Map` returning a default value if the map does not contain the requested key.
FixedSizeMap: Decorates another `Map` to fix the size, preventing add/remove.
FixedSizeSortedMap: Decorates another `SortedMap` to fix the size blocking add/remove.
Flat3Map: A `Map` implementation that stores data in simple fields until the size is greater than 3.
HashedMap: A `Map` implementation that is a general purpose alternative to `HashMap`.
IdentityMap: A `Map` implementation that matches keys and values based on `==` not `equals()`.
IdentityMap.IdentityEntry: HashEntry
LazyMap: Decorates another `Map` to create objects in the map on demand.
LazySortedMap: Decorates another `SortedMap` to create objects in the map on demand.
LinkedMap: A `Map` implementation that maintains the order of the entries.
ListOrderedMap: Decorates a `Map` to ensure that the order of addition is retained using a `List` to maintain order.
LRUMap: A `Map` implementation with a fixed maximum size which removes the least recently used entry if an entry is added when full.
MultiKeyMap: A `Map` implementation that uses multiple keys to map the value.
MultiValueMap: A MultiValueMap decorates another map, allowing it to have more than one value for a key.
PredicatedMap: Decorates another `Map` to validate that additions match a specified predicate.
PredicatedSortedMap: Decorates another `SortedMap` to validate that additions match a specified predicate.
ReferenceIdentityMap: A `Map` implementation that allows mappings to be removed by the garbage collector and matches keys and values based on `==` not `equals()`.
ReferenceMap: A `Map` implementation that allows mappings to be removed by the garbage collector.
SingletonMap: A `Map` implementation that holds a single item and is fixed size.
StaticBucketMap: A StaticBucketMap is an efficient, thread-safe implementation of `java.util.Map` that performs well in in a highly thread-contentious environment.
TransformedMap: Decorates another `Map` to transform objects that are added.
TransformedSortedMap: Decorates another `SortedMap` to transform objects that are added.
TypedMap: Decorates another `Map` to validate that elements added are of a specific type.
TypedSortedMap: Decorates another `SortedMap` to validate that elements added are of a specific type.
UnmodifiableEntrySet: Decorates a map entry `Set` to ensure it can't be altered.
UnmodifiableMap: Decorates another `Map` to ensure it can't be altered.
UnmodifiableOrderedMap: Decorates another `OrderedMap` to ensure it can't be altered.
UnmodifiableSortedMap: Decorates another `SortedMap` to ensure it can't be altered.

## Package org.apache.commons.collections.map Description

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
- IdentityMap - map that uses == for comparison instead of equals()
- Flat3Map - designed for good performance at size 3 or less
- LinkedMap - a hash map that maintains insertion order, supporting OrderedMapIterator
- 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
- Typed - ensures that only elements that are of a specific type can be added
- Transformed - transforms each element added
- FixedSize - ensures that the size of the map cannot change
- Lazy - creates objects in the map on demand
- ListOrdered - ensures that insertion order is retained

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