Java News from Wednesday, June 30, 2004

The Apache Jakarta Project has released Commons Collections 3.1, an open source library that extends and augments the Java Collections Framework. It includes:

• Bag interface for collections that have a number of copies of each object
• Buffer interface for collections that have a well defined removal order, like FIFOs
• BidiMap interface for maps that can be looked up from value to key as well and key to value
• MapIterator interface to provide simple and quick iteration over maps
• Type checking decorators to ensure that only instances of a certain type can be added
• Transforming decorators that alter each object as it is added to the collection
• Composite collections that make multiple collections look like one
• Ordered maps and sets that retain the order elements are added in, including an LRU based map
• Identity map that compares objects based on their identity (==) instead of the equals method
• Reference map that allows keys and/or values to be garbage collected under close control
• Many comparator implementations
• Many iterator implementations
• Adapter classes from array and enumerations to collections
• Utilities to test or create typical set-theory properties of collections such as union, intersection, and closure

Version 3.1 is mostly backwards compatible with 3.0. It adds a number of new classes including TreeList, MultiKeyMap, SingletonMap, ObjectGraphIterator, MapBackedSet, ReferenceIdentityMap, AbstractReferenceMap, EmptyIterator, TransformedPredicate, PredicateDecorator, and AbstractSerializableDecorator. A number of other classes are now Serializable, and various methods have been added to existing classes. And of course bugs have been fixed.