Java Examples in a Nutshell, 3rd Edition

A Clock Applet

Example 16-2 is an applet that displays the current time, as shown in Figure 16-2, and updates it once every second. Unlike Example 16-1, which defines a paint( ) method and does its own text drawing with Graphics.drawString( ), this example uses a java.awt.Label component to do the drawing. While it is common for applets to do their own drawing with a paint( ) method, it is also important to remember that applets extend java.awt.Panel and can contain any type of GUI components. Clock defines an init( ) method that creates and configures the Label component.

Figure 16-2. A clock applet

In order to update the time every second, Clock implements the Runnable interface and creates a Thread that runs the run( ) method. The applet’s start( ) and stop( ) methods are invoked by the browser when the applet becomes visible or is hidden; they start and stop the thread. (Although the example is written to use Java 1.1, it does not rely on the Thread.stop( ) method, which was deprecated in Java 1.2.)

Finally, the Clock applet implements getAppletInfo( ) to provide information about the applet. Sun’s appletviewer tool is able to display this information, but most web browsers don’t.

Example 16-2. Clock.java

package je3.applet; import java.applet.*; // Don't forget this import statement! import java.awt.*; // Or this one for the graphics! import java.util.Date; // To obtain ...