Revised: Sun Apr 03 09:25:24 CDT 2016
This page is included in the following Books:
Table of contents
- Preface
- Preview
- Discussion and sample code
- Run the program
- Summary
- What's next?
- Online video links
- Miscellaneous
- Complete program listings
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 Figuresand Listings while you are reading about them.
Figures
- Figure 1 . Program output on command line screen.
Listings
- Listing 1 . Beginning of the Prob05 class.
- Listing 2 . The class named Prob05MyClassA.
- Listing 3 . The next statement in the main method.
- Listing 4 . The class named Prob05MyClassB.
- Listing 5 . The end of the main method.
- Listing 6 . Complete program listing.
Preview
The program that I will explain in this module produces no graphics and does not require the use of Ericson's media library.
OOP concepts
The program illustrates the following OOP concepts among others:
- Multiple levels of indirection
- A one-element array of type Object
- Storing a reference to an object in an array element as type Object
- An anonymous object
- Passing a reference to a subclass object as type Object
- Downcasting an incoming object reference to access a method
Program specifications
Write a program named Prob05 that uses the class definition shown in Listing 1 to produce an output similar to that shown in Figure 1 on the command-line screen.
Figure 1 . Program output on command line screen. |
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Prob05
DickBaldwin
-28-28 |
A random value
Because the program generates and uses a random data value, the actual values displayed will differ from one run to the next. However, in all cases, the twovalues shown in Figure 1 must match.
New classes
You may define new classes as necessary to cause your program to behave as required, but you may not modify the class definition for the class named Prob05 which begins in Listing 1 .
Discussion and sample code
Will explain in fragments
I will explain this program in fragments. A complete listing is provided in Listing 6 near the end of the module.
I will begin with the driver class named Prob05 , which begins in Listing 1 .
Listing 1 . Beginning of the Prob05 class. |
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import java.util.*;
class Prob05{public static void main(String[] args){Random generator = new Random(new Date().getTime());
int randomNumber = (byte)generator.nextInt();Object[] objRef = {new Prob05MyClassA(randomNumber)}; |
Everything in Listing 1 should be familiar to you with the possible exception of the last statement, which I will explain shortly.
Characteristics of arrays in Java
Before explaining that statement, however, I will discuss some of the important characteristics of array objects in Java. A list of suchcharacteristics follows in no particular order: