Chapter 9, Problem 7PE

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 that takes the invoice number

    public void setInvoiceNumber(int num)

    {

        //Assign the value

        invoiceNumber = num;

    }

    //Define a set method that takes the amount of sale

    public void setSaleAmount(double amt)

    {

        //Assign the value

        saleAmount = amt;

        //Compute the sales tax

        tax = saleAmount * RATE;

    }

    //Define a get method that returns the amount of sale

    public double getSaleAmount()

    {

        //Return the value

        return saleAmount;

    }

    //Define a get method that returns the invoice number

    public int getInvoiceNumber()

    {

        //Return the value

        return invoiceNumber;

    }

    /*Define a method to display the invoice number,

    amount of sale, and amount of sales tax*/

    public void display()

    {

        //Print the result

        System.out.println("Invoice #" + invoiceNumber +

         "  Amount of sale: $" + saleAmount + "  Tax: $" + tax);

    }

}

File name: “SortPurchasesArray.java”

//Import necessary header files

import java.util.Scanner;

//Define a class named SortPurchasesArray

public class SortPurchasesArray

{

    //Define a main method

    public static void main(String[] args)

    {

        //Declare an array of five Purchase objects

        Purchase[] purchases = new Purchase[5];

        //Declare the variables

        int i;

        String message;

        char choice;

        final char QUIT = 'Z';

        int number;

        double price;

        //Create an object for Scanner class

        Scanner keyboard = new Scanner(System.in);

        //For loop to be executed until i exceeds 5

        for(i = 0; i < purchases.length; ++i)

        {

            //Prompt the user to enter the invoice number

            System.out.print("Enter invoice number >> ");

            number = keyboard.nextInt();

            //Prompt the user to enter the amount of sale

            System.out.print("Enter sale amount >> ");

            price = keyboard.nextDouble();

            purchases[i] = new Purchase();

            //Function call

            purchases[i].setInvoiceNumber(number);

            purchases[i].setSaleAmount(price);

        }

        keyboard.nextLine();

        /*Prompt the user to enter whether the Purchase objects

        should be sorted and displayed in invoice number

        order or sale amount order*/

System.out.print("\nSort Purchases by (I)nvoice number, or (S)ale amount? ");

        choice = keyboard.nextLine()...