I create a Vehicle super class and MyCar,MyTruck sub classes. There is @@number_of_vehicles class variables that keeps track of number of Instances instanitiated from the Sub Classes.

• And a class method that prints that class variable

But it prints 0 even after creating objects from the sub classes.

class Vehicle
  @@number_of_vehicles = 0

  def self.number_of_vehicles
    puts "This program has created #{@@number_of_vehicles} vehicles"
  end

  def self.gas_mileage(gallons, miles)
    puts "#{miles / gallons} miles per gallon of gas"
  end

  def initialize
    @@number_of_vehicles += 1
  end
end

class MyCar < Vehicle
  NUMBER_OF_DOORS = 4
  #code omitted for brevity...
end

class MyTruck < Vehicle
  NUMBER_OF_DOORS = 2
end