Everybody of you who have large experience with Java thanks Apache for their commons project. This project includes a lot of libraries to extend or simplify work with JDK. One of these libraries is commons-collections.
It was very helpful when you needed to work with specific kinds of collections like multi map, lazy collections, bidirectional map, etc. Also it had a great number of iterators, comparators and utilities to avoid writing unnecessary code in your application. It allowed us to transform one collection to another, filter collection elements and many other things very easy. It introduced completely new types of collections like buffer (collection that allows objects to be removed in some well-defined order), bag (collection that counts the number of times an object appears in the collection), bidirectional map (map that allows bidirectional lookup between key and values) and created a great number of custom implementations of existing collections types.
But why I always use past sentences? Because from the beginning of Java 5 usage this library is not more so helpful. One of the main features introduced in Java 5 was generics. And of course the most useful place for generics to be applied is collections framework. I hoped that it takes not more than year to refactor existing library and add support of generics by commons-collections developers. But it didn't happen. :( But don't worry! There are some solutions of this issue. First one is to use generics version of commons-collections developed in parallel with main Apache version. At this moment they have functionality synchronized with version 3.1. Another option is to use google-collections instead. This project was started as free time development of one developer in Google for internal usage and now it contains a lot of features in comparison to commons-collections. It is driven by community, so only really needed things are included. To start work with this library or to get your own opinion take a look at the video presentation. Develop with pleasure!
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