Using Design Patterns in the Gourmet Coffee System

Prerequisites, Goals, and Outcomes

Prerequisites: Before you begin this exercise, you need mastery of the following:

Object$-$oriented Programming

How to define interfaces

How to implement interfaces

Design Patterns:

Knowledge of the singleton pattern

Knowledge of the strategy pattern

Goals: Reinforce your ability to use the singleton and strategy patterns

Outcomes: You will demonstrate mastery in the following:

Producing applications that use the singleton pattern

Producing applications that use the strategy pattern

Background

In this assignment, you will create another version of the Gourmet Coffee System. This version will present the user with four choices:

$[0]$ Quit

$[1]$ Display sales $($Plain Text$)$

$[2]$ Display sales $($HTML$)$

$[3]$ Display sales $($XML$)$

choice$>$

The user will be able to display the sales information in three formats: plain text, HTML$,$ or XML$.$ Part of the work has been done for you and is provided in the student archive. You will implement the code that formats the sales information. This code will use the singleton and strategy patterns.

Description

The following class diagram shows how the singleton and strategy pattern will be used in your implementation:

Figure $1$ Portion of Gourmet Coffee System class diagram

Figure $1$ Portion of Gourmet Coffee System class diagram

The elements of the pattern are:

Interface SalesFormatter declares a method called formatSales that produces a string representation of the sales information.

Class PlainTextSalesFormatter implements formatSales. Its version returns the sales information in a plain$-$text format.

Class HTMLSalesFormatter implements formatSales. Its version returns the sales information in an HTML format.

Class XMLSalesFormatter implements formatSales. Its version returns the sales information in an XML format.

Class GourmetCoffee is the context class. It also contains client code. The client code calls:

Method GourmetCoffee.setSalesFormatter to change the current formatter

Method GourmetCoffee.displaySales to display the sales information using the current formatter

In this assignment, you should implement the following interface and classes:

SalesFormatter

PlainTextSalesFormatter

HTMLSalesFormatter

XMLSalesFormatter

GourmetCoffee $($a partial implementation is provided in the student archive$)$

Complete implementations of the following classes are provided in the student archive:

Coffee

CoffeeBrewer

Product

Catalog

OrderItem

Order

Sales

Interface SalesFormatter

Interface SalesFormatter declares the method that every "Formatter" class will implement.

Method:

public String formatSales$($Sales sales$).$ Produces a string representation of the sales information.

Class PlainTextSalesFormatter

Class PlainTextSalesFormatter implements the interface SalesFormatter. This class is implemented as a singleton so a new object will not be created every time the plain$-$text format is used.

Static variable:

singletonInstance$.$ The single instance of class PlainTextSalesFormatter.

Constructor and methods:

static public PlainTextSalesFormatter getSingletonInstance$().$ Static method that obtains the single instance of class PlainTextsalesFormatter.

private PlainTextSalesFormatter$().$ Constructor that is declared private so it is inaccessible to other classes. A private constructor makes it impossible for any other class to create an instance of class PlainTextSalesFormatter.

public String formatSales$($Sales sales$).$ Produces a string that contains the specified sales information in a plain$-$text format. Each order in the sales information has the following format:

$------------------------$

Order number

quantity$1$ code$1$ price$1$

quantity$2$ code$2$ price$2$

$...$

quantityN codeN priceN

Total $=$ totalCost

where

number is the order number.

quantityX is the quantity of the product.

codeX is the code of the product.

priceX is the price of the product.

totalCost is the total cost of the order.

Each order should begin with a dashed line. The first order in the sales information should be given an order number of $1,$ the second should be given an order number of $2,$ and so on$.$

Class HTMLSalesFormatter

Class HTMLSalesFormatter implements the interface SalesFormatter. This class is implemented as a singleton so a new object will not be created every time the HTML format is used.

Static variable:

singletonInstance$.$ The single instance of class HTMLSalesFormatter.

Constructor and methods:

static public HTMLSalesFormatter getSingletonInstance$().$ Static method that obtains the single instance of class HTMLSalesFormatter.

private HTMLSalesFormatter$().$ Constructor that is declared private so it is inaccessible to other classes. A private constructor makes it impossible for any other class to create an instance of class HTMLSalesFormatter.

public String formatSales$($Sales sales$).$ Produces a string that contains the specified sales information in an HTML format.

The string should begin with the following HTML:

code: code$1$

quantity: quantity$1$

price: price$1$

code: codeN

quantity: quantityN

price: priceN

code: C$001$

quantity: $5$

price: $17\mathrm{.}99$

code: C$002$

quantity: $2$

price: $18\mathrm{.}75$

code: A$001$

quantity: $2$

price: $9\mathrm{.}0$

code: B$002$

quantity: $1$

price: $200\mathrm{.}0$