Exercise $7-1$: Modify the Product Viewer application

This exercise guides you through the process of testing and modifying the Product Viewer application that's presented in this chapter.

Review and test the project:

$1.$ Open the project named ch$07\_$ex$1\_$Product that's in the ex$\_$starts folder. Then, open the Product, ProductDB, and ProductApp classes and review their code.

$2.$ Run the application and test it with valid product codes like "java", $"$jsp$",$ and $"$mysql$"$ to make sure this application works correctly. Then, test it with an invalid code to see how that works.

Modify the ProductDB class:

$3.$ In the ProductDB class, modify the if$/$else statement so it includes another product.

$4.$ Run the application and test it to make sure the new product code works. This shows that you can modify the code for a class without needing to modify the other classes that use it$.$

Add a constructor to the Product class:

$5.$ In the Product class, add a constructor that defines three parameters and uses them to set the values of the three instance variables.

$6.$ In the ProductDB class, modify the code so it uses the new constructor to set the data in the Product object instead of using the setCode$(),$ setDescription$(),$ and setPrice$()$ methods. To do that, you can assign a new Product object to the Product variable within each if$/$else clause.

$7.$ Run the application to make sure it still works correctly.

Add a method to the Product class:

$8.$ In the product class, add a method named getPriceNumberFunction$()$ that returns the price with number formatting $($not currency formatting$).$ This method should return the number with $2$ decimal places but no currency symbol.

$9.$ In the ProductApp class, modify the code so it uses the method.

$10.$ Run the application to make sure it still works correctly.

Modify the ProductDB class so it defines an object:

$11.$ IN the ProductDB class, modify the getProduct$()$ method so it's an instance method instead of a static method.

$12.$ In the ProductApp class, modify the code so it creates a ProductDB object named db$.$ Then, use this object to call the getProduct$()$ method of the ProductDB class.

$13.$ Run the application to make sure it still works correctly.

Original Product class code:

import java.text.NumberFormat;

public class Product $\{$

private String code;

private String description;

private double price;

public Product$()\{$

code $=""$;

description $=""$;

price $=0$;

$\}$

public void setCode$($String code$)\{$

this.code $=$ code;

$\}$

public String getCode$()\{$

return code;

$\}$

public void setDescription$($String description$)\{$

this.description $=$ description;

$\}$

public String getDescription$()\{$

return description;

$\}$

public void setPrice$($double price$)\{$

this.price $=$ price;

$\}$

public double getPrice$()\{$

return price;

$\}$

public String getPriceFormatted$()\{$

NumberFormat currency $=$ NumberFormat.getCurrencyInstance$()$;

return currency.format$($price$)$;

$\}$

$\}$

Original ProductDB class code:

public class ProductDB $\{$

public static Product getProduct$($String productCode$)\{$

$//$ In a more realistic application, this code would

$//$ get the data for the product from a file or database

$//$ For now, this code just uses if$/$else statements

$//$ to return the correct product data

$//$ create the Product object

Product product $=$ new Product$()$;

$//$ fill the Product object with data

product.setCode$($productCode$)$;

if $($productCode$.$equalsIgnoreCase$("$java$"))\{$

product.setDescription$("$Murach$\text{'}$s Java Programming"$)$;

product.setPrice$(57\mathrm{.}50)$;

$\}$

else if $($productCode$.$equalsIgnoreCase$("$jsp$"))\{$

product.setDescription$("$Murach$\text{'}$s Java Servlets and JSP$")$;

product.setPrice$(57\mathrm{.}50)$;

$\}$

else if $($productCode$.$equalsIgnoreCase$("$mysql$"))\{$

product.setDescription$("$Murach$\text{'}$s MySQL$")$;

product.setPrice$(54\mathrm{.}50)$;

$\}$

else $\{$

product.setDescription$("$Unknown$")$;

$\}$

return product;

$\}$

$\}$

Orignal ProductApp class code:

import java.util.Scanner;

public class ProductApp $\{$

public static void main$($String args$[])\{$

$//$ display a welcome message

System.out.println$("$Welcome to the Product Viewer"$)$;

System.out.println$()$;

$//$ display $1$ or more products

Scanner sc $=$ new Scanner$($System$.$in$)$;

String choice $="$y$"$;

while $($choice$.$equalsIgnoreCase$("$y$"))\{$

$//$ get the input from the user

System.out.print$("$Enter product code: $")$;

String productCode $=$ sc$.$nextLine$()$; $//$ read the product code

$//$ get the Product object

Product product $=$ ProductDB.getProduct$($productCode$)$;

$//$ display the output

System.out.println$()$;

System.out.println$("$SELECTED PRODUCT"$)$;

System.out.println$("$Description: $"+$ product.getDescription$())$;

System.out.println$("$Price: $"+$ product.getPriceFormatted$())$;

System.out.println$()$;

$//$ see if the user wants to continue

System.out.print$("$Continue$?($y$/$n$)$: $")$;

choice $=$ sc$.$nextLine$()$;

System.out.println$()$;

$\}$

$\}$

$\}$