Beginning Java 2- JDK 1.3 Version
Images and Animation
Try It Out – Fixed-Rate Task Execution
To make use of fixed-rate execution scheduling we'll create an applet that
is a clock. The graphics will be much more complicated than the scheduling,
but we will have an opportunity to explore yet another way of handling
animation. It's quite a lot of code so we'll put it together piece by
piece, starting with the applet class.
The basic code for the applet class will be like this:
import java.awt.*;
import javax.swing.*;
import java.awt.geom.*;
import java.util.*;
public class NewClock extends JApplet
{
// This method is called when the applet is loaded
public void init()
{
// Initialize the applet and set up the clock
}
// This method is called when the browser starts the applet
public void start()
{
// Start the clock
}
// This method is called when the browser wants to stop the applet
public void stop()
{
// Stop the clock
}
}
The class has the name NewClock to differentiate from the
myriad of other clock programs that are around. This class just contains
the three basic methods that we will need to implement for our applet. We
won't need to implement the paint() method as we will be
adding the representation of the clock to the applet object and the clock
will take care of drawing itself.
The clock when it is running will look as shown in the illustration.
We can consider the clock to be made up of two parts. One part is the face,
consisting of the circular dial plus the hour marks, and which is static.
The other part is the hands, consisting of the hour, minute, and second
hands, plus the central boss holding them in place. This is the bit that is
dynamic and has to be updated. By separating the hands from the face of the
clock, we can write our applet so that we only need to update the hands as
time passes, and avoid having to redraw the face each time we update the
time shown on the clock. We can define the two parts of the clock by inner
classes to the NewClock class. We shall bring all our
creativity to bear and name these classes ClockFace and
Hands. Let's define the first one first.
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