2.11 Java1622: array objects, part 1

Revised: Fri Apr 01 15:07:49 CDT 2016

This page is included in the following Books:

• ITSE 2321 - Object-Oriented Programming (Java)
• Object-Oriented Programming (OOP) with Java

Table of contents

• Preface
  • Viewing tip
    • Listings
• Preview
• Discussion and sample code
• Summary
• What's next?
• Miscellaneous
• Complete program listing

Preface

This module is one of a series of modules designed to teach you about Object-Oriented Programming (OOP) using Java.

Viewing tip

I recommend that you open another copy of this document in a separate browser window and use the following links to easily find and view the listings while you are reading about them.

Listings

• Listing 1 . Sample variable declarations for array objects.
• Listing 2 . The special case of type Object.
• Listing 3 . Creating array objects.
• Listing 4 . The beginning of the class named Array05.
• Listing 5 . A new ordinary object of class Array05.
• Listing 6 . Populate the second element.
• Listing 7 . Print some data.
• Listing 8 . Produce some more output.
• Listing 9 . Complete program listing.

Preview

This module explains how array objects fit into the grand scheme of things in Object-Oriented Programming (OOP) using Java.

A different syntax is required to create array objects than the syntax normally used to create ordinary objects.

Array objects are accessed via references. Any of the methods of the Object class can be called on a reference to an array object.

Array objects encapsulate a group of variables. The variables don't have individual names. They are accessed using positive integer index values. Theinteger indices of a Java array object always extend from 0 to (n-1) where n is the length of the array encapsulated in the object.

All array objects in Java encapsulate one-dimensional arrays. The component type of an array may itself be an array type. This makes it possible to createarray objects whose individual components refer to other array objects. This is the mechanism for creating multi-dimensional or ragged arrays in Java.

Discussion and sample code

Three kinds of objects

In an earlier module, I told you that from a conceptual viewpoint, there are at least three kinds of objects involved in a Java program:

• Ordinary objects
• Class objects
• Array objects

Ordinary objects

Most of the discussion up to that point in the collection dealt with what I have referred to in the above list as ordinary objects .

These are the objects that you instantiate in your code by applying the new operator to a constructor for a class in order to create a new instance (object) of that class.

Class objects

In that module that discussed Class objects, I emphasized that my discussion of Class objects was conceptual in nature and did not necessarily represent an actual implementation.I went on to discuss the class named Class , and discussed how the use of that class fits into the grand scheme of OOP in Java. I explained how theexistence of class variables and class methods tends to complicate the rather simple OOP structure consisting only of ordinary objects.