Decorator Pattern

Objectives

During this activity:

Students will write and test Ruby code that implements the Decorator pattern.

This activity helps students develop the following skills, values and attitudes: ability to analyze and synthesize, capacity for identifying and solving problems, and efficient use of computer systems.

Activity Description

This activity can be developed individually or in pairs.

This example was taken from [FREEMAN] pp. 79-98.

Create a folder called decorator. Inside this folder, create two files called: coffee.rb, and tc_coffee.rb.

All Ruby source files must start with a comment containing the lab's title, date, and the authors' personal information. For example:
```
# Decorator Pattern
# Date: 17-Oct-2014
# Authors:
#          A00456654 Thursday Rubinstein 
#          A01160611 Anthony Stark
```

Write the code that allows us to model coffee beverages using the Decorator pattern. The following tables show what beverages and condiments are available, and their corresponding prices:

*Beverages*
Name	Price
Dark Roast Coffee	$0.99
Espresso	$1.99
House Blend Coffee	$0.89

*Condiments*
Name	Price
Mocha	$0.20
Whip	$0.10
Soy	$0.15
Milk	$0.10

In our design, the condiments will decorate the beverages. The following Ruby code demonstrates how your code could be used:

beverage = DarkRoast.new
beverage = Mocha.new(beverage)
beverage = Whip.new(beverage)
puts beverage.description
puts beverage.cost

For this example, the expected output should be:

Dark Roast Coffee, Mocha, Whip
1.29

The following image depicts the way the decorators work when the cost method is called from the above code.

A decorated beverage.

The following UML diagram shows the class hierarchy. Each class needs to implement one or several of these methods: initialize, description, and cost.

Beverage class hierarchy.

All these classes should be placed in the coffee.rb source file.

The following unit tests verify the correct behavior of your classes. Place the test class in the tc_coffee.rb source file.

# File: tc_coffee.rb

require 'test/unit'
require 'coffee'

class MyTest < Test::Unit::TestCase

  def test_espresso
    beverage = Espresso.new
    assert_equal("Espresso", beverage.description)
    assert_equal(1.99, beverage.cost)
  end

  def test_dark_roast
    beverage = DarkRoast.new
    beverage = Milk.new(beverage)
    beverage = Mocha.new(beverage)
    beverage = Mocha.new(beverage)
    beverage = Whip.new(beverage)
    assert_equal("Dark Roast Coffee, Milk, Mocha, Mocha, Whip", beverage.description)
    assert_equal(1.59, beverage.cost)
  end

  def test_house_blend
    beverage = HouseBlend.new
    beverage = Soy.new(beverage)
    beverage = Mocha.new(beverage)
    beverage = Whip.new(beverage)
    assert_equal("House Blend Coffee, Soy, Mocha, Whip", beverage.description)
    assert_equal(1.34, beverage.cost)
  end

end

Deliverables

Create a compressed tarball file with the full contents of the decorator directory. Call this file decorator.tgz. From a terminal, you can use the following command to create this file (make sure to run it at the same level where the decorator folder resides):

tar czf decorator.tgz decorator

✔ Upload Instructions

To deliver the decorator.tgz file, please provide the following information:

Request PIN

Due date is Sunday, October 19.

S/W Design and Architecture

Decorator Pattern

Objectives

Activity Description

Deliverables

✔ Upload Instructions