Java Applet
Applet is a special type of program that is
embedded in the webpage to generate the dynamic content. It runs inside the
browser and works at client side.
Advantage of Applet
There are many advantages of applet. They are as
follows:
- It
works at client side so less response time.
- Secured
- It
can be executed by browsers running under many plateforms, including
Linux, Windows, Mac Os etc.
Drawback of Applet
- Plugin
is required at client browser to execute applet.
Do You Know
- Who is
responsible to manage the life cycle of an applet ?
- How to perform
animation in applet ?
- How to paint
like paint brush in applet ?
- How to display
digital clock in applet ?
- How to display
analog clock in applet ?
- How to
communicate two applets ?
Hierarchy of Applet
|
As displayed
in the above diagram, Applet class extends Panel. Panel class extends
Container which is the subclass of Component.
|
Lifecycle of Java Applet
- Applet
is initialized.
- Applet
is started.
- Applet
is painted.
- Applet
is stopped.
- Applet
is destroyed.
Lifecycle methods for Applet:
The java.applet.Applet class 4 life cycle
methods and java.awt.Component class provides 1 life cycle methods for an
applet.
java.applet.Applet class
For creating any applet java.applet.Applet class
must be inherited. It provides 4 life cycle methods of applet.
- public
void init(): is
used to initialized the Applet. It is invoked only once.
- public
void start(): is
invoked after the init() method or browser is maximized. It is used to
start the Applet.
- public
void stop(): is
used to stop the Applet. It is invoked when Applet is stop or browser is
minimized.
- public
void destroy(): is
used to destroy the Applet. It is invoked only once.
java.awt.Component class
The Component class provides 1 life cycle method
of applet.
- public
void paint(Graphics g): is used to paint the Applet.
It provides Graphics class object that can be used for drawing oval,
rectangle, arc etc.
Who is responsible to manage the life cycle of
an applet?
Java Plug-in software.
How to run an Applet?
There are two ways to run an applet
- By
html file.
- By
appletViewer tool (for testing purpose).
Simple example of Applet by html file:
To execute the applet by html file, create an
applet and compile it. After that create an html file and place the applet code
in html file. Now click the html file.
1. //First.java
2. import java.applet.Applet;
3. import java.awt.Graphics;
4. public class First extends Applet{
5.
6. public void paint(Graphics g){
7. g.drawString("welcome",150,150);
8. }
9.
10. }
Note: class must be public because its object is
created by Java Plugin software that resides on the browser.
myapplet.html
1. <html>
2. <body>
3. <applet code="First.class" width="300" height="300">
4. </applet>
5. </body>
6. </html>
Simple example of Applet by appletviewer tool:
To execute the applet by appletviewer tool,
create an applet that contains applet tag in comment and compile it. After that
run it by: appletviewer First.java. Now Html file is not required but it is for
testing purpose only.
1. //First.java
2. import java.applet.Applet;
3. import java.awt.Graphics;
4. public class First extends Applet{
5.
6. public void paint(Graphics g){
7. g.drawString("welcome to applet",150,150);
8. }
9.
10. }
11. /*
12. <applet code="First.class" width="300" height="300">
13. </applet>
14. */
To execute the applet by appletviewer tool,
write in command prompt:
c:\>javac First.java
c:\>appletviewer First.java
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