Introduction

In Chapter 17, we discussed how to create and manipulate data structures. The discussion was "low level" in the sense that we painstakingly created each element of each data structure dynamically and modified the data structures by directly manipulating their elements and the references to their elements. In this chapter, we consider the Java collections framework, which contains prepackaged data structures, interfaces and algorithms for manipulating those data structures. Some examples of collections are the cards you hold in a card game, your favorite songs stored in your computer, the members of a sports team and the real-estate records in your local registry of deeds (which map book numbers and page numbers to property owners). In this chapter, we also discuss how generics (see Chapter 18) are used in the Java collections framework.

With collections, programmers use existing data structures, without concern for how they are implemented. This is a marvelous example of code reuse. Programmers can code faster and can expect excellent performance, maximizing execution speed and minimizing memory consumption. In this chapter, we discuss the collections framework interfaces that list the capabilities of each collection type, the implementation classes, the algorithms that process the collections, and the so-called iterators and enhanced for statement syntax that "walk through" collections. This chapter provides an introduction to the collections framework. For complete details, visit java.sun.com/j2se/5.0/docs/guide/collections.

The Java collections framework provides ready-to-go, reusable componentryyou do not need to write your own collection classes, but you can if you wish to. The collections are standardized so that applications can share them easily without concern with for details of their implementation. The collections framework encourages further reusability. As new data structures and algorithms are developed that fit this framework, a large base of programmers will already be familiar with the interfaces and algorithms implemented by those data structures.