Apache Commons Collections - Overview


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Commons Collections augments Java Collections Framework. It provides several features to make collection handling easy. It provides many new interfaces, implementations and utilities. Main features of Commons Collections are following −

  • Bag − Bag interfaces simplifies the collections which have multiple number of copies of each object.

  • BidiMap − BidiMap interfaces provide Bi-Directional maps which can be used to lookup values using keys or keys using values.

  • MapIterator − MapIterator interface provide simple and easy iteration over maps.

  • Transforming Decorators − Transforming decorators can alter every object of a collection as and when it is added to the collection.

  • Composite Collections − Composite collections are used where multiple collections are required to be handled uniformly.

  • Ordered Map − Ordered Maps retain the order in which elements are added in.

  • Ordered Set − Ordered Sets retain the order in which elements are added in.

  • Reference map − Reference map allows key/values to be garbage collected under close control.

  • Comparator implementations − Many Comparator implementations are available.

  • Iterator implementations − Many Iterator implementations are available.

  • Adapter Classes − Adapter classes are available to convert array and enumerations to collections.

  • Utilities − Utilities are available to test test or create typical set-theory properties of collections such as union, intersection. Supports Closure.



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