The Java Collections Framework

A collections framework is a unified architecture for representing and manipulating collections. All collections frameworks contain three things:

Interfaces: abstract data types representing collections. Interfaces allow collections to be manipulated independently of the details of their representation. In object-oriented languages like Java, these interfaces generally form a hierarchy
Implementations: concrete implementations of the collection interfaces. In essence, these are reusable data structures
Algorithms: methods that perform useful computations, like searching and sorting, on objects that implement collection interfaces. These algorithms are said to be polymorphic because the same method can be used on many different implementations of the appropriate collections interface. In essence, algorithms are reusable functionality.