Application Framework

To use the MVC Framework, developers create a customization that extends the framework:

The Framework

Here's a simplified version of the framework's design:

The framework uses the following patterns:

Model-View-Controller
Model = Model
View = View
Controller = Command Processor

Publisher-Subscriber
Publisher = Observable
Subscriber = Observer
Concrete Publisher = Model
Concrete Observer = View

Command Processor
Command Processor = Command Processor
Command = Command

Memento
Caretaker = Command
Memento = Memento
Originator = Model

The View

Here are a few details of the View class design:

Views are JPanels. They have two menus: File (New, Save, SaveAs, Open, Exit) and Edit (Undo, Redo, etc.). There are two inner classes called FileController and EditController that listen to these menus.

The View also instantiates the Abstract Factory pattern:

Abstract Products = Commands & Model
Abstract Factory = View

Programmers will provide the concrete products and factory in the customization (see below).

A Customization (Stoplight Simulator)

Here's a screen shot of the Stoplight Simulator:

Under the Edit menu is an additional item called change. Repeatedly selecting this item causes the lights to change from red, to green, to yellow, and back to red again.

Here's the design of the simulator:

Perhaps the trickiest part is the StopLightView class:

public class StopLightView extends View {

public StopLightView(StopLight model) {
super(model);
title = "Stop Light Simulation";
windowHeight = 300;
windowWidth = 300;
JMenuItem changeItem = new JMenuItem("Change");
changeItem.addActionListener(ec);
editMenu.add(changeItem);
}

public void paintComponent(Graphics gc) {
StopLight model = (StopLight)theModel;
StopLight.State state = model.getState();

if (state.equals(StopLight.State.STOP)) {
gc.setColor(Color.RED);
} else {
gc.setColor(Color.BLACK);
}
gc.fillOval(10, 10, 10, 10);
if (state.equals(StopLight.State.SLOW)) {
gc.setColor(Color.YELLOW);
} else {
gc.setColor(Color.BLACK);
}
gc.fillOval(10, 30, 10, 10);
if (state.equals(StopLight.State.GO)) {
gc.setColor(Color.GREEN);
} else {
gc.setColor(Color.BLACK);
}
gc.fillOval(10, 50, 10, 10);
}

// three oveerrides:
public Model makeModel() {
return new StopLight();
}

public Command makeCommand(String cmmd) {
System.out.println("COMMAND = " + cmmd);
if (cmmd.equals("Change")) {
return new ChangeCommand((StopLight)theModel);
} else {
return null;
}
}

public void update(Observable arg0, Object arg1) {
repaint();
}

public static void main(String[] args) {
// TODO Auto-generated method stub
StopLightView gui = new StopLightView(new StopLight());
gui.display();

}
}

Notes:

1. This class is the main class (i.e., contains main).

2. This class overrides paintComponent, inherited from JPanel. This simply draws the stop light using information from the stoplight model.

3. This class overrides the update method. The call to repaint() forces the OS to call paintComponent.

4. This class is a concrete factory overriding factory methods that make needed components: model and commands. In this case the model is an instance of StopLight. The ChangeCommand is the concrete product manufactured by makeCommand. Note that this method can produce many types of commands, depending on the input.

5. The constructor makes an additional menu item, then adds it to the edit menu.

Source Code

Study the code below for more details on how this framework is designed, implemented, and used.

mvc.zip (An Eclipse project)

framework

customization1