Commons Collections 4.0 API;

Commons-Collections contains implementations, enhancements and utilities that complement the Java Collections Framework.

See:
Description

Packages

org.apache.commons.collections	This package contains the interfaces and utilities shared across all the subpackages of this component.
org.apache.commons.collections.bag	This package contains implementations of the Bag and SortedBag interfaces.
org.apache.commons.collections.bidimap	This package contains implementations of the BidiMap, OrderedBidiMap and SortedBidiMap interfaces.
org.apache.commons.collections.buffer	This package contains implementations of the Buffer interface.
org.apache.commons.collections.collection	This package contains implementations of the Collection interface.
org.apache.commons.collections.comparators	This package contains implementations of the Comparator interface.
org.apache.commons.collections.functors	This package contains implementations of the Closure, Predicate, Transformer and Factory interfaces.
org.apache.commons.collections.iterators	This package contains implementations of the Iterator interface.
org.apache.commons.collections.keyvalue	This package contains implementations of collection and map related key/value classes.
org.apache.commons.collections.list	This package contains implementations of the List interface.
org.apache.commons.collections.map	This package contains implementations of the Map, IterableMap, OrderedMap and SortedMap interfaces.
org.apache.commons.collections.set	This package contains implementations of the Set and SortedSet interfaces.

Commons-Collections contains implementations, enhancements and utilities that complement the Java Collections Framework.

The Apache Jakarta Commons Collections Framework component adds a significant amount of enhancements to the standard JDK collections. These enhancements come in the form of new interfaces, new implementations and utility classes.

See also the java.util package for the standard Java collections.

Main features

Commons-Collections defines a number of key interfaces:

Interface	Description
Bag	A new Collection subinterface that stores each object together with the number of occurances. Methods are provided to get the number of occurances, and to add and remove a certain number of that object.
Buffer	A new Collection subinterface that allows objects to be removed in some well-defined order. Methods enable the next item to be peeked and removed.
BidiMap	A new Map subinterface that allows lookup from key to value and from value to key with equal ease.
OrderedMap	A new Map subinterface that is used when a map has an order, but is not sorted. Methods enable bidriectional iteration through the map.
MapIterator	A new Iterator subinterface specially designed for maps. This iterator avoids the need for entrySet iteration of a map, and is simpler to use.
ResettableIterator	A new Iterator subinterface that allows the iteration to be reset back to the start. Many iterators in this library have this functionality.
Closure Predicate Transformer Factory	A group of functor interfaces that provide plugin behaviour to various collections and utilities.

In addition to the interfaces, there are many implementations. Consult each subpackage for full details of these.