Chapter 6, Problem 15PE

a.

Explanation of Solution

Program:

File name: “Purchase.java”

//Define a class named Purchase

public class Purchase

{

    //Declare the private variables

    private int invoiceNumber;

    private double saleAmount;

    private double tax;

    private static final double RATE = 0.05;

    //Define a set method for the invoice number

    public void setInvoiceNumber(int num)

    {

        invoiceNumber = num;

    }

    //Define a set method for the sale amount

    public void setSaleAmount(double amt)

    {

        //Calculate the sales tax as 5% of the sale amount

        saleAmount = amt;

        tax = saleAmount * RATE;

    }

�...

b.

Explanation of Solution

Program:

File name: “CreatePurchase.java”

//Import necessary header files

import javax.swing.*;

//Define a class named CreatePurchase

public class CreatePurchase

{

    //Define a main method

    public static void main(String[] args)

    {

        //Declare Purchase object

        Purchase purch = new Purchase();

        //Declare the variables

        int num;

        double amount;

        String entry;

        final int LOW = 1000, HIGH = 8000;

        //Prompt the user to enter the invoice number

entry = JOptionPane.showInputDialog(null, "Enter invoice number");

        num = Integer.parseInt(entry);

        /*While the user does not enter a number between 1,000 and 8,000*/

        while(num <= LOW || num >= HIGH)

        {

            //Print the message

entry = JOptionPane.showInputDialog(null, "Invoice number must be between " +

            LOW + " and " + HIGH + "\nEnter invoice number");

            num = Integer...