1. 30
Java Applets

2. Previously
Packages
Structure
Packages Views

3. Overview Java Applets Characteristics JApplet Methods Hello World
Applet Life Cycle
Deployment

4. Lunch an Applet!

5. Characteristics
Java Plug-in software in the browser manages the lifecycle of an applet
Applets uses the browser services
Web Server
Storage
Browser
Library (y) OS
Applet
applet

6. JApplet JApplet class is in javax.swing package
Applets inherit significant functionality from the JApplet class
Capabilities to communicate with the browser
Capability to present a graphical user interface (GUI) to the user
JApplet provides a root pane which is the same top-level component structure as JFrame

7. JApplet Inherit from JApplet Override method public void init()
Called when the applet is loaded into the browser

8. Methods init() start() stop() destroy()
Called when the applet is loaded into the browser
start()
Override if need to do some tasks after initialization
stop()
Should suspend the execution of the applet, so that it does not take up system resources when the user is not viewing the applet
destroy()
Perform all tasks necessary to shut down the applet
stop() is called before destroy() so if overriding stop it may not be needed to override destroy

9. Hello World public class HelloWorldGUI extends JApplet {
/**
* Hello World as a Java applet. *
aasco */
public class HelloWorldGUI extends JApplet {
* A version number for this class so that serialisation can occur without
* worrying about the underlying class changing between serialisation and
* deserialisation.
* <br>
* Not that we ever serialise this class of course, but JApplet implements
* Serializable, so therefore by default we do as well.
private static final long serialVersionUID = L;
* Builds the GUI and adds the message.
@Override
public void init() {
JLabel jlbHelloWorld = new JLabel(" Hello World!");
add(jlbHelloWorld); // add label to the GUI
} // init()
} // end class HelloWorldGUI

10. Applet Life Cycle
When the page, where the applet is to appear, is displayed then an instance of the applet is created
When leaving the page where the applet appear, e.g. to go to another page, the browser stops and destroys the applet

11. Applet Life Cycle
When refresh or reload the page the applet appear in the browser, the current instance of the applet is stopped and destroyed and a new instance is created
When closing the browser the applet has the opportunity of doing some cleanup

12. Deployment Compile code
Create JAR file with compiled code and resources
Create the HTML page
Use the Applet Tag inside the HTML page
<applet code="com.aasco.fizbuz.gui.FizBuzApplet" archive="fizBuz.jar" width="900" height="500">
<param name="type" value="rnd" />
</applet>
Place the JAR file and HTML page in the appropriate folder