Objectives

In this section another example is presented of the notion of abstract systems and the employment of event-driven control to maintain a consistent display of the internal state of the system.

Points to emphasize

Hints

An event has only two important moments in its lifetime: its creation and its activation. The activation of an event may possibly be repeated. The class event is an abstract class. Its derived classes implement actual events, corresponding to actions of the user of a system.

Question

  1. Explain how events may be used to regulate the effects of user actions. Why are events needed?

Comments

The notion of events employed in this section resembles the notion of events employed in discrete event simulation systems. Both allow to be activated in response to a user action. Discrete event simulation, however, may involve explicit timing constraints and scheduling policies.