An Applet is
a java program that is transmitted over the network from server to the client
and execute within browser of client. Applets are used to provide interactivity
in web application.
It is a
managed object. Managed object is an object that is created and managed by a
run time environment. Lifecycle methods
are used to manage the lifecycle of a managed object.
Applets are
managed object because their objects are created and managed by the Browser or another
Java applet viewing program, such as the Applet Viewer.
init():
executed only once when an object of the applet is created. This method is used
for initialization purpose.
public void
init();
start():represents
the entry point of an apple, it is executed initially after init() and
subsequently each time execution of the applet resume.
public void
start();
stop():
executed each time execution of the applet is suspended.
public void
stop();
paint():used
to draw the contents of an applet. It is executed initially after start and
subsequently each time repaint() is invoke or applet is redraw by the
container.
public void
paint(Graphics g);
destroy():executed
when an applet object is unloaded form memory.
public void
destroy();
Graphics: Object of graphics class
represents the graphics environment of a GUI component. Each GUI component has
a graphics object associated with it that determines contents of the GUI
component. Graphics Class provides
various methods to draw components.
drawstring()
: draw a string on a GUI component.
public void
drawstring(String text, int left, int top)
Another
methods are drawLine(), drawRect(), drawOval()
Limitation
An Applet
has the following limitations:
1. An applet can only initiate socket
communication with the host form which it was downloaded.
2. An applet cannot access local file
system on the client machine.
3. An applet can only request basic
information, such as name and version of OS, version of JRE from the client machine.
4. And applet does not have main method
because its execution is predetermined by the life cycle method.
<applet>
tag is used to embed the applet within an html page.
<applet
code="ClassName.class" width="350"
height="350"></applet>
Simple Example:
1. Create a Java Source File
package
helloapplet;
import
java.applet.Applet;
import
java.awt.Graphics;
/**
*
* @author Navindra Jha
*/
public class
MyApplet extends Applet {
@Override
public void paint(Graphics g) {
g.drawString("Hello
applet!", 50, 25);
}
}
2. Compile the Source File
If
the compilation succeeds, the compiler creates a file named MyApplet.class
3. Create an HTML File that Includes
the Applet
<HTML>
<HEAD>
<TITLE>
A Simple Program </TITLE>
</HEAD>
<BODY>
<APPLET
code="MyApplet.class" width=150 height=25>
</APPLET>
</BODY>
</HTML>
4. Run the Applet
To run the
applet, you need to load the HTML file into an application that can run Java
applets. This application might be a Java-compatible browser or another Java
applet viewing program, such as the Applet Viewer.
How To Run Applet On Netbeans
1. Right-click the HelloApplet project
and choose Properties to open the Properties window.
2. Right-click the HelloApplet project
node in the Projects window and select New > Other (Ctrl-N).
3. Under Categories, select Java. Under
File Types, select Applet.
4. Under Class Name, type MyApplet.
Under Package, type helloapplet
5. Click Finish.
The IDE
creates the applet source file in the specified package. The applet source file
opens in the Source editor.
6. Define your applet class like below
package
helloapplet;
import
java.applet.Applet;
import
java.awt.Graphics;
/**
*
* @author Navindra Jha
*/
public class
MyApplet extends Applet {
@Override
public void paint(Graphics g) {
g.drawString("Hello
applet!", 50, 25);
}
}
7. Right-click the MyApplet.java file
node in the Projects window and choose Run File from the contextual menu. The
applet is launched in the Applet Viewer.
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