Ruby class methods vs. instance methods

example_def.rb

class Human

  # Class method (a.k.a. static method)
  def self.classification
    'Mammal'
  end


  # Instance constructor
  def initialize(first_name, last_name)
    @my_first_name = first_name
    @my_last_name  = last_name
  end


  # Instance method
  def full_name
    "#{@my_first_name} #{@my_last_name}"
  end
end

example_usage.rb

puts Human.classification    # => 'Mammal'

puts Human.full_name         # => NoMethodError: undefined method 'full_name' for Human:Class


# Create a new instance of the Human class
teresa = Human.new('Teresa', 'Nestle-Quik')

puts teresa.classification   # => NoMethodError: undefined method 'classification' for #<Human:0x1e820>

puts teresa.full_name        # => 'Teresa Nestle-Quik'