Java Applets

Name: Richa Sharma PRN: 060341044 Subject: WDT Presentation

 Applet: Special kind of java program that a Javaenabled browser can download from internet and then run.

 Hopes: Hopes Users can access their s/w from any java enabled computer or device with an internet connection.

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Html: (used to describe layout of a web page) simply a vehicle to indicate elements of a hypertext page.

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“How to use Applets in a web page?” The html page uses a tag that tells the browser the following: 3. Where to get the class file… 4. How the applet is positioned on the web page(size,location,etc)… 

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The Browser then retrieves the class files from the internet and automatically runs the applet,using an JRE or JVM.

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In addition to the applet itself,the web can have other html element on web pages(multiple fonts,bulleted lists,graphics,links..)..

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Thus, Java applet is not a tool for designing html pages,it is a tool for ‘bringing them to life’..

A Bit of History… Initially Sun’s Hot Java browser required.. Netscape followed by IE include a JVM.. Problem: inability to adapt to new versions…  Solution:

Sun’s “Java plug-in” tool.  Installation of the current version: http://java.sun.com/getjava

An applet is simply a ‘java class’ that extends the java.applet.Applet class. Although applet is an AWT component,we generally use SWING to implement applets: So,applets are made to extend ‘JApplet’,the super class for swing applets.

/* The following HTML tags are required to display this applet in a browser */ import javax.swing.*; public class NotHelloWorldApplet extends Japplet { public void init() { JLabel label = new JLabel("Not a Hello,Worldapplet",SwingConstants.CENTER); add(label); } }

To execute the applet,we can carry out the following: Compile your java source files into class files. Create an HTML file that tells the browser which class file to load first and how to size the applet.

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In ‘appletviewer’.

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In a browser.

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Is a part of JDK that helps in testing of the web page before loading it on the net.

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At the command line,we give the following: appletviewer NotHelloWorldApplet.html

To get hold of user’s perspective. The real view. You need: 1. Java 2 enabled browser. 2. To load the html file into the browser

The NotHelloWorldApplet.java looks like:

 Code: tells the browser how to locate the applet.  Width, height: size the window holding the applet.

The when called,what it does and action examples of: Public void init( ):  Applet loaded for execution.  Initializes the applet.  Processing parameter values,adding user interface components.

Public void start( ):  After init completes execution.  User moves to some other site & later return to the applet’s html page.  Starting animation,threads of execution.

Public void paint(Graphics g):  after init and start.  When applet needs to be repainted.  Drawing with graphics object g that is passed to the paint method by the

applet container.

Public void stop( ):  User leaves applet page.  Tasks required to suspend the applet execution.  Stops execution of animation,threads etc.

Public void destroy( ):  Applet being removed from memory.  User exits browsing session.  Clean up all resources allocated to the applet.

Sand box security model: “code executing in the ‘sandbox’ is not allowed to ‘play outside the sandbox’. Some important sites:  For applets resources:

java.sun.comjar  For some of the best applets on net:

www.jars.com

Summary … Applet and basics. History. The inheritance hierarchy. An example. Execution of applet. Applet viewing Html tags and attributes Applet life cycle methods. Some sites.

Thank you…