Java Collections

The Java collections framework (JCF) is a set of classes and interfaces that implement commonly reusable collection data structures.

Although referred to as a framework, it works in a manner of a library. The JCF provides both interfaces that define various collections and classes that implement them.

Collections and arrays are similar in that they both hold references to objects and they can be managed as a group. However, unlike arrays, collections do not need to be assigned a certain capacity when instantiated. Collections can also grow and shrink in size automatically when objects are added or removed. Collections cannot hold basic data type elements (primitive types) such as int, long, or double; instead, they hold Wrapper Classes such as Integer, Long, or Double.

Collection implementations in pre-JDK 1.2 versions of the Java platform included few data structure classes, but did not contain a collections framework. The standard methods for grouping Java objects were via the array, the Vector, and the Hashtable classes, which unfortunately were not easy to extend, and did not implement a standard member interface.

To address the need for reusable collection data structures, several independent frameworks were developed, the most used being Doug Lea's Collections package, and ObjectSpace Generic Collection Library (JGL), whose main goal was consistency with the C++ Standard Template Library (STL).

The collections framework was designed and developed primarily by Joshua Bloch, and was introduced in JDK 1.2. It reused many ideas and classes from Doug Lea's Collections package, which was deprecated as a result. Sun chose not to use the ideas of JGL, because they wanted a compact framework, and consistency with C++ was not one of their goals.

...
Wikipedia