Intro to Classes

Intro to Classes

Warmup

  • Define a method sum that takes two numbers as arguments and returns their sum
  • Define a method hello that returns the string “Hello, and welcome!”
  • Define a method print_hello that prints the string “Hello, and welcome!” to the screen
  • Wrap these methods in a class called Calculator
  • Create a new instance of our Calculator class and call the methods you defined

Defining a Class

class ClassName
end

Converter Class

# converter.rb
class Converter
  # convert, print_welcome, convert_to_celsius, print_converted
end

Converter Runner File

# converter_runner.rb (in the same directory as `converter`)

require './converter'

converter = Converter.new
converter.convert(32, 35, 100)
puts "This is our converter: #{converter}"

Behavior and State

  • Behavior: what an instance of our class does
  • State: what it is or has: characteristics, status, and possessions

Car

  • Behavior: start, stop, turn, speed up, slow down
  • State: color, passengers, wheels, current speed, mileage

Creating Class with State

State is stored in instance variables

class Classroom
  def initialize(length, width, height)
    @length = length
    @width  = width
    @height = height
  end
end

Classroom Runner

# classroom_runner.rb (same directory as `classroom.rb`)
require './classroom'

classroom_a = Classroom.new(10, 5, 20)
puts classroom_a

Pulling State

# classroom_runner.rb
require './classroom'

classroom_a = Classroom.new(10, 5, 20)
puts "Length: #{classroom_a.length}"

Providing Means to Get State

# classroom.rb
class Classroom
  attr_reader :length,
              :width,
              :height

  def initialize(length, width, height)
    @length = length
    @width  = width
    @height = height
  end
end

Adding Behavior

# classroom.rb

class Classroom
  attr_reader :length,
              :width,
              :height

  def initialize(length, width, height)
    @length = length
    @width  = width
    @height = height
  end

  def area
    length * width
  end
end

Adding Behavior to Runner

# classroom_runner.rb
require './classroom'

classroom_a = Classroom.new(10, 5, 20)
puts "Length: #{classroom_a.length}"
puts "Width: #{classroom_a.width}"
puts "Area: #{classroom_a.area}"

Changing State

  • With a method
  • Changing our attr_reader to attr_accessor (can be done selectively)

Changing State in Classroom

# classroom.rb
class Classroom
  attr_accessor :length,
                :width,
                :height

  # ... initialize, area

  def add_length(feet)
    @length += feet
  end
end

Changing State from Our Runner

# classroom_runner.rb
require './classroom'

classroom_a = Classroom.new(10, 5, 20)
puts "Length: #{classroom_a.length}"
puts "Width: #{classroom_a.width}"
puts "Area: #{classroom_a.area}"

puts "Make length 1."
classroom_a.length = 1

puts "New Length: #{classroom_a.length}"
puts "New Area: #{classroom_a.area}"

puts "Add four to length"
classroom_a.add_length(4)

puts "New Length: #{classroom_a.length}"
puts "New Area: #{classroom_a.area}"

Try It!

  • Create a Lunchbox class that has a theme, height, width, and length attributes
  • Allow users to access the theme
  • Create a method capacity that returns the total volume the lunchbox can hold

Summary

  • How would you define a Cubby class in Ruby?
  • What might be some of its attributes?
  • What might be some of its methods?

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