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Beginning Java 2- JDK 1.3 Version : Images and Animation

Buy this book Title: Beginning Java 2- JDK 1.3 Version ISBN: 1861003668 US Price: $ 49.99 Canadian Price: C$ 74.95 UK Price: £ 35.99 Publication Date: March 2000 Pages: 1230 © Wrox Press Limited, US and UK.

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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