Revised: Sat Apr 02 20:33:36 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 Figures and Listings while you are reading about them.
Figures
- Figure 1 . Program output on the command line screen.
- Figure 2 . Default behavior of the toString method.
- Figure 3 . More on the default behavior of the toString method.
Listings
- Listing 1 . Source code for class Prob04.
- Listing 2 . Beginning of the class named Prob04MyClass.
- Listing 3 . Override the abstract getData method.
- Listing 4 . Override the toString method.
- Listing 5 . 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:
- Extending an abstract class.
- Parameterized constructor.
- Defining an abstract method in the superclass and overriding it in a subclass.
- Overridden toString method.
Program specifications
Write a program named Prob04 that uses the class definition shown in Listing 1 to produce the output on the command-line screen shown in Figure 1 .
| Figure 1 . Program output on the command line screen. |
|---|
Prob04
DickBaldwin
9595 |
Pseudo random data
Because the program generates and uses a pseudo random data value each time it is run, the actual values displayed in the last two lines of Figure 1 will differ from one run to the next. However, in all cases, the two values 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 Prob04 given below.
Discussion and sample code
Will explain in fragments
I will explain this program in fragments. A complete listing is provided in Listing 5 near the end of the module.
I will begin with the driver class named Prob04 , which is shown in its entirety in Listing 1 .
| Listing 1 . Source code for class Prob04. |
|---|
import java.util.*;
abstract class Prob04{public static void main(String[] args){Random generator = new Random(new Date().getTime());
int randomNumber = (byte)generator.nextInt();Prob04 objRef = new Prob04MyClass(randomNumber);System.out.println(objRef);
System.out.println(objRef.getData());System.out.println(randomNumber);
}//end main//Declare the signature of an abstract class.
public abstract int getData();}//end class Prob04 |
The import directive
The import directive at the beginning of Listing 1 is required because the program requires access to the Random class and the Date class, both of which are defined in the java.util package.