This package contains implementations of the {@link org.apache.commons.collections.BidiMap BidiMap}, {@link org.apache.commons.collections.OrderedBidiMap OrderedBidiMap} and {@link org.apache.commons.collections.SortedBidiMap SortedBidiMap} interfaces. A BidiMap is an extension to Map that allows keys and values to be looked up with equal ease. One example usage is a system communicating to a legacy datasource that must convert codes from the new format to the old format and vice versa.

The following implementations are provided in the package:

- DualHashBidiMap - uses two HashMaps to implement BidiMap
- DualTreeBidiMap - uses two TreeMaps to implement SortedBidiMap
- TreeBidiMap - red-black tree implementation of OrderedBidiMap

The following decorators are provided in the package:

- Unmodifiable - ensures the map cannot be altered