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Learn about abstract methods, abstract classes, and overridden methods. You will also learn about overriding the toString method.

Revised: Sat Apr 02 20:33:36 CDT 2016

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Table of contents

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.

Questions & Answers

how did you get 1640
Noor Reply
If auger is pair are the roots of equation x2+5x-3=0
Peter Reply
Wayne and Dennis like to ride the bike path from Riverside Park to the beach. Dennis’s speed is seven miles per hour faster than Wayne’s speed, so it takes Wayne 2 hours to ride to the beach while it takes Dennis 1.5 hours for the ride. Find the speed of both bikers.
MATTHEW Reply
420
Sharon
from theory: distance [miles] = speed [mph] × time [hours] info #1 speed_Dennis × 1.5 = speed_Wayne × 2 => speed_Wayne = 0.75 × speed_Dennis (i) info #2 speed_Dennis = speed_Wayne + 7 [mph] (ii) use (i) in (ii) => [...] speed_Dennis = 28 mph speed_Wayne = 21 mph
George
Let W be Wayne's speed in miles per hour and D be Dennis's speed in miles per hour. We know that W + 7 = D and W * 2 = D * 1.5. Substituting the first equation into the second: W * 2 = (W + 7) * 1.5 W * 2 = W * 1.5 + 7 * 1.5 0.5 * W = 7 * 1.5 W = 7 * 3 or 21 W is 21 D = W + 7 D = 21 + 7 D = 28
Salma
Devon is 32 32​​ years older than his son, Milan. The sum of both their ages is 54 54​. Using the variables d d​ and m m​ to represent the ages of Devon and Milan, respectively, write a system of equations to describe this situation. Enter the equations below, separated by a comma.
Aaron Reply
find product (-6m+6) ( 3m²+4m-3)
SIMRAN Reply
-42m²+60m-18
Salma
what is the solution
bill
how did you arrive at this answer?
bill
-24m+3+3mÁ^2
Susan
i really want to learn
Amira
I only got 42 the rest i don't know how to solve it. Please i need help from anyone to help me improve my solving mathematics please
Amira
Hw did u arrive to this answer.
Aphelele
hi
Bajemah
-6m(3mA²+4m-3)+6(3mA²+4m-3) =-18m²A²-24m²+18m+18mA²+24m-18 Rearrange like items -18m²A²-24m²+42m+18A²-18
Salma
complete the table of valuesfor each given equatio then graph. 1.x+2y=3
Jovelyn Reply
x=3-2y
Salma
y=x+3/2
Salma
Hi
Enock
given that (7x-5):(2+4x)=8:7find the value of x
Nandala
3x-12y=18
Kelvin
please why isn't that the 0is in ten thousand place
Grace Reply
please why is it that the 0is in the place of ten thousand
Grace
Send the example to me here and let me see
Stephen
A meditation garden is in the shape of a right triangle, with one leg 7 feet. The length of the hypotenuse is one more than the length of one of the other legs. Find the lengths of the hypotenuse and the other leg
Marry Reply
how far
Abubakar
cool u
Enock
state in which quadrant or on which axis each of the following angles given measure. in standard position would lie 89°
Abegail Reply
hello
BenJay
hi
Method
I am eliacin, I need your help in maths
Rood
how can I help
Sir
hmm can we speak here?
Amoon
however, may I ask you some questions about Algarba?
Amoon
hi
Enock
what the last part of the problem mean?
Roger
The Jones family took a 15 mile canoe ride down the Indian River in three hours. After lunch, the return trip back up the river took five hours. Find the rate, in mph, of the canoe in still water and the rate of the current.
cameron Reply
Shakir works at a computer store. His weekly pay will be either a fixed amount, $925, or $500 plus 12% of his total sales. How much should his total sales be for his variable pay option to exceed the fixed amount of $925.
mahnoor Reply
I'm guessing, but it's somewhere around $4335.00 I think
Lewis
12% of sales will need to exceed 925 - 500, or 425 to exceed fixed amount option. What amount of sales does that equal? 425 ÷ (12÷100) = 3541.67. So the answer is sales greater than 3541.67. Check: Sales = 3542 Commission 12%=425.04 Pay = 500 + 425.04 = 925.04. 925.04 > 925.00
Munster
difference between rational and irrational numbers
Arundhati Reply
When traveling to Great Britain, Bethany exchanged $602 US dollars into £515 British pounds. How many pounds did she receive for each US dollar?
Jakoiya Reply
how to reduced echelon form
Solomon Reply
Jazmine trained for 3 hours on Saturday. She ran 8 miles and then biked 24 miles. Her biking speed is 4 mph faster than her running speed. What is her running speed?
Zack Reply
d=r×t the equation would be 8/r+24/r+4=3 worked out
Sheirtina
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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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