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Applet in Java

An applet, a Java programme, can be added to your website. Within a web browser, this applet runs client-side. You can host the applet on a web server and embed it directly into an HTML page by using the object or applet tag. This gives your website a lively and enjoyable touch.
- Every applet is a subclass of the java.applet.Applet class. Applets don't work on their own; they run inside an applet viewer or a web browser. The applet viewer is a common tool provided by JDK.
- Unlike regular programs that start from the main() method, applets have a different way of starting to run.

Table Of Content

Applet in Java
Life cycle of an applet
Applet Example
How to run an Applet
Applets' advantages over HTML
Restrictions imposed on Java applets

Instead of using System.out.println for displaying output in the applet window, AWT methods like drawString() are used.
Your website can be made more interactive and interesting for your visitors by using java applets.

Hierarchy of Applet in Java

Life cycle of an applet

In Java applet there are 4 life cycle methods for applets in the applet class, and 1 life cycle methods for applets in the java.awt.Component class.

java.applet.Applet class
- void init() : The init() method is the first one to be called when your applet starts. Its main purpose is to initialize variables. It's essential to note that this method is executed only once during the entire runtime of your applet.
- void start() : After init(), the start() method is called. It acts as a way to restart the applet after it has been stopped. One thing to keep in mind is that start() gets called every time the applet's HTML document is displayed on the screen. On the other hand, init() is only triggered once when the applet is initially loaded. This means that if a user leaves the web page and returns, the applet resumes from the beginning.
- void stop() : When a web browser navigates away from the HTML document containing the applet, such as when it changes to another page, the stop() method is invoked. It is likely that the applet is running when stop() is called. When the applet is not visible, threads that are unnecessary to run should be suspended using the stop() function. If the user revisits the page, you can restart them when start() is called.
- void destroy() : When your applet needs to be removed entirely from memory, the destroy() method is called by the environment. At this point, you should release any resources that the applet might be using. Prior to destroy(), the stop() method is always invoked.
java.awt.Component class
- paint() : The Applet has been painted using paint (Graphics Gra). It offers objects of the Graphics class, which can be used to draw shapes like arcs, rectangles, ovals and circle

Simple example of Applet by html file

import java.applet.Applet;
import java.awt.Graphics;
public class Main extends Applet{
    @Override    // Overriding paint() method
    public void paint(Graphics g){
        g.drawString("Hello India", 40, 40);
    }    
}

html file

<html>  
<body>  
     <applet 
       code="Main.class" width="250" height="250">  
     </applet>  
   </body>  
</html>

How to run an Applet?

There are two accepted methods for running an applet.

In a web browser that supports Java.
Using an applet viewer like the common tool applet-viewer. This is usually the quickest and simplest way to test your applet.

Simple example of Applet by appletviewer tool

import java.applet.Applet;
import java.awt.Graphics;
public class Main extends Applet{
	@Override // Overriding paint() method
	public void paint(Graphics g){
	   g.drawString("Hello India", 40, 40);
	} 
}

/* <applet code="Main.class" width=250 height=250> </applet> */

Output:

Hello India

Applets' advantages over HTML

Dynamic Web Pages: Applets enable the display of dynamic web pages, making the user experience more interactive and engaging.
Audio Integration: Applets allow seamless integration of audio files into web applications, enhancing multimedia capabilities.
Document Presentation: With applets, documents can be presented in a more interactive and user-friendly manner.
Animation Playback: Applets facilitate smooth playback of animations, adding visual appeal to web pages.

Restrictions imposed on Java applets

No Native Methods or Libraries: Applets cannot define native methods or load external libraries, restricting their access to certain functionalities.
Limited File Access: Typically, applets cannot read or write to files on the host system, ensuring security and privacy.
Limited File Access: Typically, applets cannot read or write to files on the host system, ensuring security and privacy.
Network Connection Limitation: Applets can only connect to the host they originated from when establishing network connections.
No Execution of Host Programs: Applets cannot start any running program on the host system, preventing potential security risks.

Animation in Applet Next »

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Applet in Java

Hierarchy of Applet in Java

Life cycle of an applet

java.applet.Applet class

java.awt.Component class

Simple example of Applet by html file

html file

How to run an Applet?

Simple example of Applet by appletviewer tool

Applets' advantages over HTML

Restrictions imposed on Java applets

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