Chapter 8

Arrays

COMPUTERS GET A LOT OF THEIR POWER from working with data structures. A data structure is an organized collection of related data. An object is a type of data structure (although it is in fact more than this, since it also includes operations or methods for working with that data). However, this type of data structure -- consisting of a fairly small number of named instance variables -- is only one of the many different types of data structure that a programmer might need. In many cases, the programmer has to build more complicated data structures by linking objects together. But there is one type of data structure that is so important and so basic that it is built into every programming language: the array.

An array is a data structure consisting of a numbered list of items, where all the items are of the same type. In Java, the items in an array are always numbered from zero up to some maximum value, which is set when the array is created. For example, an array might contain 100 integers, numbered from zero to 99. The items in an array can belong to one of Java's primitive types. They can also be references to objects, so that you could, for example, make an array containing all the Buttons in an applet.

This chapter discusses how arrays are created and used in Java. It also covers the standard class java.util.Vector. An object of type Vector is very similar to an array object.

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