Lab 6: Adapter Pattern

Objectives

During this lab session:

Students will write and test Ruby code that implements the Adapter 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

The lab activities can be developed individually or in pairs.

The lab report must be developed individually.

Create a folder called adapter. Inside this folder, create three files called: simple_queue.rb, queue_adapter.rb, and test_adapter.rb.

All three Ruby source files must start with a comment containing the lab's title, date, and the authors' personal information. For example:
```
# Lab 6: Adapter Pattern
# Date: 28-Sep-2011
# Authors:
# 456654  Anthony Stark 
# 1160611 Thursday Rubinstein
```

The content of the file simple_queue.rb is as follows:

# File: simple_queue.rb

# IMPORTANT: Do not modify the following class in any way!

class SimpleQueue
  
  def initialize
    @info =[]
  end
  
  def insert(x)
    @info.push(x)
    self
  end
  
  def remove
    if empty?
      raise "Can't remove if queue is empty"
    else
      @info.shift
    end
  end
  
  def empty?
    @info.empty?
  end
  
  def size
    @info.size
  end
  
  def inspect
    @info.inspect
  end
end

The SimpleQueue class contains a First-In First-Out (FIFO) data structure that implements the following methods:

Method Signature	Description
`insert(x)`	Inserts x at the back of this queue. Returns this queue.
`remove`	Removes and returns the element at the front of this queue. Raises an exception if this queue happens to be empty.
`empty?`	Returns `true` if this queue is empty, otherwise returns `false`.
`size`	Returns the number of elements currently stored in this queue.

Write an adapter class called QueueAdapter (place it in the file called queue_adapter.rb) that makes a SimpleQueue instance (as implemented above) behave like a Last-In First-Out (LIFO) stack with the following interface:

Method Signature	Description
`initialize(q)`	Initializes a new stack, using q as the adaptee.
`push(x)`	Inserts x at the top of this stack. Returns this stack.
`pop`	Returns `nil` if this stack is empty, otherwise removes and returns its top element.
`peek`	Returns nil if this stack is empty, otherwise returns its top element without removing it.
`empty?`	Returns `true` if this stack is empty, otherwise returns false.
`size`	Returns the number of elements currently stored in this stack.

The following unit test verifies the correct behavior of the QueueAdapter class. Place the test class in the test_adapter.rb source file.

# File: test_adapter.rb 

require 'test/unit'
require 'simple_queue'
require 'queue_adapter'

class QueueAdapterTest < Test::Unit::TestCase  

  def test_queue_adapter    
    q = SimpleQueue.new
    qa = QueueAdapter.new(q)
    assert q.empty?
    assert qa.empty?
    assert_nil qa.pop 
    qa.push("Foo")
    assert_equal "Foo", qa.peek
    assert !q.empty?
    assert !qa.empty?
    qa.push("Bar")
    assert_equal "Bar", qa.peek
    qa.push("Baz").push("Quux")
    assert_equal 4, q.size
    assert_equal 4, qa.size
    assert_equal "Quux", qa.peek
    assert_equal "Quux", qa.pop
    assert_equal "Baz", qa.peek
    assert_equal "Baz", qa.pop
    assert_equal "Bar", qa.peek
    assert_equal "Bar", qa.pop
    assert_equal "Foo", qa.peek
    qa.push("Goo")
    assert_equal "Goo", qa.peek
    assert_equal "Goo", qa.pop
    assert_equal "Foo", qa.peek
    assert_equal 1, qa.size
    assert_equal "Foo", qa.pop
    assert_nil qa.peek
    assert_nil qa.pop
    assert q.empty?
    assert qa.empty? 
    assert_equal 0, q.size
    assert_equal 0, qa.size
  end
  
end

Deliverables

To hand in your individual lab work, follow these instructions.

Write your lab report in English according to the specified guidelines. Name your AsciiDoc source file lab6_report_A0MMMMMMM.txt, where A0MMMMMMM is your student ID. From your AsciiDoc source, generate the corresponding HTML file. That file should be called lab6_report_A0MMMMMMM.html. Place these two files in the adapter directory.
Create a tarball file with the full contents of the adapter directory. Call this file adapter.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 adapter folder resides):
```
tar czf adapter.tgz adapter
```
Using the Online Assignment Delivery System (SETA), deliver the tarball file.

Due date is Tuesday, October 4.

Evaluation

This activity will be evaluated using the following criteria:

50%	Implementation of functional requirements.
50%	Lab report.
DA	The program and/or report was plagiarized.

Software Design and Architecture

Lab 6: Adapter Pattern

Objectives

Activity Description

Deliverables

Evaluation