— Scott McNealy, Sun Microsystems Chairman, President and ceo

controller 
events

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getting 
gui
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This final version builds on version two by adding the GUI parts. We build a 
frame, add a drawing panel to it, and each time we get an event, we draw a 
new rectangle and repaint the screen. The only other change from version 
two is that the notes play randomly as opposed to simply moving up the 
scale. 
The most important change to the code (besides building a simple GUI) 
is that we make the drawing panel implement the ControllerEventListener 
rather than the program itself. So when the drawing panel (an inner class) 
gets the event, it knows how to take care of itself by drawing the rectangle.
Complete code for this version is on the next page.
Version Three: drawing graphics in time with the music
 class MyDrawPanel extends JPanel implements ControllerEventListener {

boolean msg = false;
public void controlChange(ShortMessage event) {
msg = true;
repaint();
}
public void paintComponent(Graphics g) {
if (msg) {

Graphics2D g2 = (Graphics2D) g;
int r = (int) (Math.random() * 250);
int gr = (int) (Math.random() * 250);
int b = (int) (Math.random() * 250);
g.setColor(new Color(r,gr,b));
int ht = (int) ((Math.random() * 120) + 10);
int width = (int) ((Math.random() * 120) + 10);
int x = (int) ((Math.random() * 40) + 10);
int y = (int) ((Math.random() * 40) + 10);
g.fillRect(x,y,ht, width);
msg = false;
} // close if
} // close method
} // close inner class
The drawing panel inner class:
The drawing panel is a listener
We set a flag to false, and we’ll set it 
to true only when we get an event. 
We got an event, so we set the flag to 
true and call repaint()
We have to use a flag because OTHER things might trigger a repaint(), 
and we want to paint ONLY when there’s a ControllerEvent
The rest is code to generate 
a random color and paint a 
semi-random rectangle.

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