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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

Initializing the Applet

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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