A plastic injection molding machine has an object oriented programmed routine to control the molding cycle of the machine. The programmed routine implements the inter-related molding cycle of clamp, inject, hold, eject and recover by development of classes corresponding to machine structure performing basic molding cycle steps. The basic classes use object oriented concepts of data encapsulation, inheritance, polymorphism, abstraction and the like that are linked together to produce objects during run time. The classes in turn include controller, observer and actuators classes. The controller class functions as a state machine. The observer class functions to determine the current state and the actuator class produces command signals controlling class related machine hardware. A modeling system is also disclosed for constructing the OO programmed routine for any injection molding machine using existing classes, principally by difference.