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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

what's economic
kamal Reply
Management of money such as saving.
babu
study of how society manage it's scare resources
Maulik
Please help me how to compute national income. what are those included on national income like for an example in W= WAGE what included in wage ?
love Reply
what is competitive market?
Shantal Reply
a compataive market is when there are many producers competating to provide consumers with a goods and services needed
Tanveer
in a compitative market no single producer or consumer can dictate the market
Tanveer
where many buyer and many seller interact for particular good or service, all buyers and sellers have negligible affect on market price.
Maulik
types of demand elasticity
Farouq Reply
What is price elasticity of demand and its degrees. also explain factors determing price elasticity of demand?
Yutansh Reply
Price elasticity of demand (PED) is use to measure the degree of responsiveness of Quantity demanded for a given change on price of the good itself, certis paribus. The formula for PED = percentage change in quantity demanded/ percentage change in price of good A
GOH
its is necessarily negative due to the inverse relationship between price and Quantity demanded. since PED carries a negative sign most of the time, we will usually the absolute value of PED by dropping the negative sign.
GOH
PED > 1 means that the demand of the good is price elasticity and for a given increase in price there will be a more then proportionate decrease in quantity demanded.
GOH
PED < 1 means that the demand of the good is price inelasticity and for a given increase in price there will be a less then proportionate decrease in quantity demanded.
GOH
The factors that affects PES are: Avaliablilty of close substitutes, proportion of income spent on the good, Degree of necessity, Addiction and Time.
GOH
Calculate price elasticity of demand and comment on the shape of the demand curve of a good ,when its price rises by 20 percentage, quantity demanded falls from 150 units to 120 units.
Helen Reply
5 %fall in price of good x leads to a 10 % rise in its quantity demanded. A 20 % rise in price of good y leads to do a 10 % fall in its quantity demanded. calculate price elasticity of demand of good x and good y. Out of the two goods which one is more elastic.
Helen
what is labor
Grace Reply
labor is any physical or mental effort that helps in the production of goods and services
Kwabena
what is profit maximizing level of out put for above hypothetical firm TC = Q3 - 21Q2 + 600 + 1800 P = 600 MC = 3Q2 - 42Q + 600
Sosna Reply
consider two goods X and Y. When the price of Y changes from 10 to 20. The quantity demanded of X changes from 40 to 35. Calculate cross elasticity of demand for X.
Sosna
sorry it the mistake answer it is question
Sosna
consider two goods X and Y. When the price of Y changes from 10 to 20. The quantity demanded of X changes from 40 to 35. Calculate cross elasticity of demand for X.
Sosna
The formula for calculation income elasticity of demand is the percent change in quantity demanded divided by the percent change in income.
Sosna
what is labor productivity
Lizzy Reply
if the demand function is q=25-4p+p² 1.find elasticity of demand at the point p=5?
Puja Reply
what are some of the difference between monopoly and perfect competition market
Obeng Reply
n a perfectly competitive market, price equals marginal cost and firms earn an economic profit of zero. In a monopoly, the price is set above marginal cost and the firm earns a positive economic profit. Perfect competition produces an equilibrium in which the price and quantity of a good is economic
Naima
what are some characteristics of monopoly market
Obeng Reply
explicit cost is seen as a total experiences in the business or the salary (wages) that a firm pay to employee.
Idagu Reply
what is price elasticity
Fosua
...
krishna
it is the degree of responsiveness to a percentage change in the price of the commodity
Obeng
economics is known to be the field
John Reply
what is monopoly
Peter Reply
what is taxation
Peter
is the compulsory transfer of wealth from the private sector to the public sector
Jonna
Difference between extinct and extici spicies
Amanpreet Reply
in a comparison of the stages of meiosis to the stage of mitosis, which stages are unique to meiosis and which stages have the same event in botg meiosis and mitosis
Leah Reply
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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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