0.2 Jbs1020-classes

Table of contents

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

Preface

This module is one in a series of modules designed to teach you about the essence of Object-Oriented Programming (OOP) using Java with particularemphasis on accessibility for blind students.

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 figuresand listings while you are reading about them.

Figures

• Figure 1 . Screen output.

Listings

• Listing 1 . The class named Radio01.
• Listing 2 . Constructing a Radio object.
• Listing 3 . Programming the radio buttons.
• Listing 4 . Pressing a button on the radio.
• Listing 5 . The Radio class.
• Listing 6 . An instance variable.
• Listing 7 . The setStationNumber method.
• Listing 8 . The playStation method.
• Listing 9 . The program named Radio01.

Preview

This module will concentrate primarily on a discussion of the Java class.

A simple Java program will be discussed to illustrate the definition and use of two different classes. Taken in combination, these two classes simulate the manufacture and the use of the car radio object discussed in an earlier module.

You will see how to write code to create a new Radio object by applying the new operator to the class named Radio . You will also see how to save that object's reference in a reference variable of type Radio .

You will see how to write code that is used to simulate the association of a radio button with a particular radio station.

You will see how to write code that is used to simulate the pressing of a radio button to play the radio station associated with that button.

You will see the definition of a class named Radio01 . This class consists simply of the main method. The main method of a Java application is executed by the Java Virtual Machine when the application is run. Thus, it is the driver for the entire application.

You will see the definition of a class named Radio . This class includes one instance variable and two instance methods.

(The instance variable is a reference variable that refers to a special kind of object that I refer to as an array object. I will provide a very brief discussion on array objects in this module. I will have more to say about array objects in a subsequent module.)

I will provide a short discussion of class variables, which are not used in this program. I will explain that the use of class variables can often lead to undesirable side effects.

Finally, I will provide a very brief discussion of the syntax of a simple class definition in Java.

Discussion and sample code

What is a class?

I explained in an earlier module that a class is a plan from which many objects can be created. I likened the class definition to the plans from which millions of nearly identical car radios can be produced.