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Learn about indirection, array objects, and casting.

Revised: Sun Apr 03 09:25:24 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 Figuresand Listings while you are reading about them.

Figures

  • Figure 1 . Program output on command line screen.

Listings

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.
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.
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:

Questions & Answers

Ayele, K., 2003. Introductory Economics, 3rd ed., Addis Ababa.
Widad Reply
can you send the book attached ?
Ariel
?
Ariel
What is economics
Widad Reply
the study of how humans make choices under conditions of scarcity
AI-Robot
U(x,y) = (x×y)1/2 find mu of x for y
Desalegn Reply
U(x,y) = (x×y)1/2 find mu of x for y
Desalegn
what is ecnomics
Jan Reply
this is the study of how the society manages it's scarce resources
Belonwu
what is macroeconomic
John Reply
macroeconomic is the branch of economics which studies actions, scale, activities and behaviour of the aggregate economy as a whole.
husaini
etc
husaini
difference between firm and industry
husaini Reply
what's the difference between a firm and an industry
Abdul
firm is the unit which transform inputs to output where as industry contain combination of firms with similar production 😅😅
Abdulraufu
Suppose the demand function that a firm faces shifted from Qd  120 3P to Qd  90  3P and the supply function has shifted from QS  20  2P to QS 10  2P . a) Find the effect of this change on price and quantity. b) Which of the changes in demand and supply is higher?
Toofiq Reply
explain standard reason why economic is a science
innocent Reply
factors influencing supply
Petrus Reply
what is economic.
Milan Reply
scares means__________________ends resources. unlimited
Jan
economics is a science that studies human behaviour as a relationship b/w ends and scares means which have alternative uses
Jan
calculate the profit maximizing for demand and supply
Zarshad Reply
Why qualify 28 supplies
Milan
what are explicit costs
Nomsa Reply
out-of-pocket costs for a firm, for example, payments for wages and salaries, rent, or materials
AI-Robot
concepts of supply in microeconomics
David Reply
economic overview notes
Amahle Reply
identify a demand and a supply curve
Salome Reply
i don't know
Parul
there's a difference
Aryan
Demand curve shows that how supply and others conditions affect on demand of a particular thing and what percent demand increase whith increase of supply of goods
Israr
Hi Sir please how do u calculate Cross elastic demand and income elastic demand?
Abari
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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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