Adapter Pattern

Objectives

During this activity:

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

This activity can be developed individually or in pairs.

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

All three Ruby source files must start with a comment containing title, date, and the authors' personal information. For example:
```
# Adapter Pattern
# Date: 01-Mar-2017
# Authors:
#          A00456654 Thursday Rubinstein 
#          A01160611 Anthony Stark
```

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 adapter_test.rb source file.

# File: adapter_test.rb 

require 'minitest/autorun'
require 'simple_queue'
require 'queue_adapter'

class QueueAdapterTest < Minitest::Test

  def test_queue_adapter
    q = SimpleQueue.new
    qa = QueueAdapter.new(q)
    assert q.empty?
    assert qa.empty?
    assert_nil qa.pop
    assert_same qa, qa.push("Foo")
    assert_equal "Foo", qa.peek
    refute q.empty?
    refute qa.empty?
    assert_same qa, qa.push("Bar")
    assert_equal "Bar", qa.peek
    assert_same qa, 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
    assert_same qa, 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

Create a compressed 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

✔ Upload Instructions

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

Request PIN

Due date is Wednesday, March 1.

S/W Design and Architecture

Adapter Pattern

Objectives

Activity Description

Deliverables

✔ Upload Instructions