2. Applets
An applet is a Java program that a browser can
download and run.
An applet is embedded inside a web page and runs in
the context of a browser.
An applet must be a subclass of the
java.applet.Applet class.
Swing provides javax.swing.JApplet.
3. Sample Applet Code
Two steps to turning it in to an Applet
1. Change "extend JFrame" to "extends JApplet" and get rid of the main, you'll have to
import javax.swing.JApplet
public class MyApp extends JApplet {
...
} // end MyApp
2. Embed the application into the webpage, using html
<html>
<head>
<title> My Applet </title
</head>
<body>
<! this is the applet tag which has attributes, there must be code, width, height>
<applet code = "MyApp.class” width = "300” height = "300”>
<! there can be optional parameters >
<param name="someParamName" value="paramStringValue" >
</applet>
</body>
</html>
4. Applet Life Cycle
loaded -> created -> initialized -> started <=> stopped -> destroyed
The applet maybe stopped because the user has changed focused
JApplet has methods initialized, started, stopped and destroyed phases.
They have default behavior that you can over write.
init() - this where you can load the parameter, someParamName, with their
String values using getParamter("someParamName"). Note that order is
not important.
start() - here you can start things after stopping
stop() - allows you save information before stopping and to use in start()
destroy() - allows you clean up. Note stop will be called first.
5. Applets have restrictions:
Cannot read or write files on the client machine
Cannot run programs on the client machine
Cannot make any computer connections
But the Applet can read data files on the Sever
6. Steps to create Applet Projects in
Netbeans
Choose File > New Project (Ctrl-Shift-N). Under
Categories, select Java.
Choose one of the following:
If you are creating a new applet source file, select Java Class
Library under Projects. Click Next.
If you want to import an applet source file, select Java Project
with Existing Sources. Click Next. Specify the file's location in
the Source Packages Folder text box.
Under Project Name, type HelloApplet. Change the
Project Location to any folder on your computer.
Click Finish.
7. Create applet source file
Right-click the HelloApplet project and choose Properties
to open the Properties window.
Select the desired Source / Binary Format for the project
from source tab.
Right-click the HelloApplet project node in the Projects
window and select New > Other (Ctrl-N).
Under Categories, select Java. Under File Types, select
Applet.
(for visual design applet select Swing GUI Forms > JApplet
Form.)
Give name to applet and click finish.
