760: Mainline

The model–view approach leads to applications defined in terms of four class types:

• Model classes, which embody domain knowledge
• View classes, which embody information-display knowledge
• Observer classes and listener classes, which embody knowledge about connections between models and views
• One application class, which both serves as a view and performs the following services:
  • Creates model, view, observer, and listener instances
  • Connects model instances to view instances, via observer instances, and view instances to model instances, via listener instances
  • Establishes container–component relations among the views

The application class serves as a view because it provides the master container, such as a frame, that creates a window for the application on a screen.