Apache Commons Collections 4.5.0 API

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

The Apache 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:

Interfaces

Interface	Description
Bag	A new Collection subinterface that stores each object together with the number of occurrences. Methods are provided to get the number of occurrences, and to add and remove a certain number of that object.
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 bidirectional 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 behavior to various collections and utilities.

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

Packages

Package	Description
org.apache.commons.collections4	Interfaces and utilities shared across all packages.
org.apache.commons.collections4.bag	Implements the Bag and SortedBag interfaces.
org.apache.commons.collections4.bidimap	Implements the BidiMap, OrderedBidiMap and SortedBidiMap interfaces.
org.apache.commons.collections4.bloomfilter	Implements Bloom filter classes and interfaces.
org.apache.commons.collections4.collection	Implementations of the Collection interface.
org.apache.commons.collections4.comparators	Implements the Comparator interface.
org.apache.commons.collections4.functors	Implements the Closure, Predicate, Transformer and Factory interfaces.
org.apache.commons.collections4.iterators	Implements the Iterator interface.
org.apache.commons.collections4.keyvalue	Implements collection and map related key/value classes.
org.apache.commons.collections4.list	Implements the List interface.
org.apache.commons.collections4.map	Implements the Map, IterableMap, OrderedMap and SortedMap interfaces.
org.apache.commons.collections4.multimap	Implements the MultiValuedMap interfaces.
org.apache.commons.collections4.multiset	Implements the MultiSet interface.
org.apache.commons.collections4.properties	Extends and customizes the behavior of Properties.
org.apache.commons.collections4.queue	Implements the Queue interface.
org.apache.commons.collections4.sequence	Compares two sequences of objects.
org.apache.commons.collections4.set	Implements the Set, SortedSet and NavigableSet interfaces.
org.apache.commons.collections4.splitmap	Implements the "split map" concept.
org.apache.commons.collections4.trie	Implements the Trie interface.
org.apache.commons.collections4.trie.analyzer	Implements KeyAnalyzer.