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CIS3023: Programming Fundamentals for CIS Majors II
Summer 2010
Introduction to Applets
Course Lecture Slides
29th July 2010
Ganesh Viswanathan
Applets
Applets are small applications accessed on an
Internet server, transported over the
networks, automatically installed and run as
part of a web document.
At the client, applets get limited access to resources to be
able to produce graphics, multimedia UI, run computations,
etc. without risk of viruses or breaching data integrity.
Applets
Applet Code Example: HelloWorld.java
import java.awt.Graphics;
import java.applet.Applet;
public class HelloWorld extends Applet{
public void paint(Graphics g){
g.drawString("Hello World!", 120, 80);
}
}
Applets
Web document: HelloWorld.html
<HTML>
<HEAD><TITLE>Applet example</TITLE>
</HEAD>
<BODY>
<APPLET code="HelloWorld.class" width="300px"
height="200px"></APPLET>
</BODY>
</HTML>
Abstract Window Toolkit (AWT)
• The Abstract Window Toolkit (AWT) is Java's original
platform-independent windowing, graphics, and userinterface widget toolkit.
• Applets interact with the user through the AWT, not
through the console-based I/O classes.
• AWT is a part of Java Foundation Classes (JFC), the
standard API for providing a graphical user interface
(GUI) for a Java program.
Abstract Window Toolkit (AWT)
• AWT contains support for a window-based,
graphical interface.
• AWT supports graphics through components (visible
UI elements-buttons/ labels/ textfields) and
containers (components that contain and organize
other components).
• All containers inherit from the java.awt.Container
base class, which itself inherits from
java.awt.Component
Applets
• Do not have main() method
• Instead applet begins execution when the
name of its class is passed to an applet viewer
or to a network browser.
Compile the applet in the same way as a normal java
application)
In the example, the paint() method defined by AWT and
overridden by the applet helps to redraw output on screen.
Applets
• Applets are event-driven.
• User initiates interaction with an applet.
These interactions are sent to the applet as
“events” to which the applet must respond.
Example: When the user clicks on a button in
the applet window, a button-click event is
generated.
Applets
In your applet override a set of methods that
help the browser or applet-viewer to interface
to the applet and control its execution.
Applet class defines – init(), start(), stop(),
destroy()
AWT Component class defines paint() method.
import java.awt.*;
import java.applet.*;
Applet Skeleton
public class MyAppletSkeleton extends Applet {
// browser calls init when applet is first loaded
public void init( ){ /* initialization */ }
// called second, after init. Also called whenever applet is restarted
public void start( ){ /* start or resume execution */ }
//called when the applet is stopped
public void stop( ){ /* suspends execution */ }
//called when applet is terminated. Last method executed
public void destroy( ){ /* perform shutdown operations */ }
//called when an applet’s window must be restored (redrawn)
public void paint(Graphics g){ /* redisplay contents of window */ }
}
import java.awt.*;
import java.applet.*;
Applet Skeleton
public class MyAppletSkeleton extends Applet {
// browser calls init when applet is first loaded
public void init( ){ /* initialization */ }
// called second, after init. Also called whenever applet is restarted.
public void start( ){ /* start or resume execution */ }
//called when the applet is stopped.
public void stop( ){ /* suspends execution */ }
//called when applet is terminated. Last method executed.
public void destroy( ){ /* perform shutdown operations */ }
//called when an applet’s window must be restored (redrawn)
public void paint(Graphics g){ /* redisplay contents of window */ }
}
Applets
Further examples.
Get more info!
• Java docs: java.applet
http://download-llnw.oracle.com/javase/1.5.0/docs/api/java/applet/packagesummary.html
• Java docs: java.awt
http://java.sun.com/j2se/1.5.0/docs/api/java/awt/package-summary.html
http://java.sun.com/products/jdk/awt/#what
• JFC
http://docstore.mik.ua/orelly/java-ent/jfc/ch02_04.htm#jfcnut-ch-2-tab-awtcont
