Beginning Java 2- JDK 1.3 Version
Images and Animation
Initializing the Applet
In the init() method we will need to create the
ClockFace object and the Hands object that will
make up the clock. We just have to decide how the hands are going to
overlay the clock face.
Back in Chapter 12 we saw how a JFrame object had several
window panes, including a content pane, to which you
typically add the components you want to display, plus a glass
pane that overlays the content pane. An object of type
JApplet has exactly the same pane structure. We can add an
object of type ClockFace to the content pane for the applet,
and make the Hands object the glass pane. As long as it's
transparent, the content pane with its ClockFace component
will be visible underneath the glass pane – which will be our
Hands object. In fact in general, a glass pane can be any
object of a class that has as a superclass. To replace the default glass
pane with your component, you just call the setGlassPane()
method for the applet object with a reference to your component as the
argument. Here's the code for the init() method that will set
our clock up like that:
public void init()
{
Dimension size = getSize(); // Get the applet size
// Create the clockface to fit within the applet
int clockDiameter = Math.min(size.width, size.height)*9/10;
clock = new ClockFace(clockDiameter);
getContentPane().add(clock); // Add clockface to content pane
hands = new Hands(clockDiameter); // Create the hands panel
setGlassPane(hands); // Make the hands the glass pane
hands.setVisible(true); // Set glass pane visible
}
We get the size of the applet by calling getSize(), and use
that to decide the diameter of the clock. Ninety percent of the smaller of
the width and height of the applet is a suitable choice to make it fit
comfortably. Once we have created the ClockFace object, we
just add it to the content pane for the applet. We then create the Hands
object and pass it to setGlassPane() to make it the glass pane
for the applet. Note that we must call setVisible() for the
glass pane because it will be set as invisible by default.
That's all that's necessary to create the visual appearance of the clock.
We just need to set it going somewhere, and that's the job of the
start() method for the applet object.
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