CSI 3125, Preliminaries, page 1 Applet

CSI 3125, Preliminaries, page 2 Applet An applet is a Java program that runs in a Web browser. An applet can be a fully functional Java application. There are some important differences between an applet and a standalone Java application And they are

CSI 3125, Preliminaries, page 3 Applet An applet is a Java class that extends the java.applet.Applet class. A main() method is not invoked on an applet, and an applet class will not define main(). Applets are designed to be embedded within an HTML page. A JVM is required to view an applet. The JVM can be either a plug-in of the Web browser or a separate runtime environment. Applets have strict security rules that are enforced by the Web browser.

CSI 3125, Preliminaries, page 4 Applet & Application Applet Small Program Used to run a program on client Browser Applet is portable and can be executed by any JAVA supported browser. Applet applications are executed in a Restricted Environment Applets are created by extending the java.applet.Applet Application Large Program Can be executed on stand alone computer system Need JDK, JRE, JVM installed on client machine. Application can access all the resources of the computer Applications are created by writing public static void main(String[] s) method.

CSI 3125, Preliminaries, page 5 Applet & Application Applet Applet application has 5 methods which will be automatically invoked on occurance of specific event Example: import java.awt.*; import java.applet.*; public class Myclass extends Applet { public void init() { } public void start() { } public void stop() {} public void destroy() {} public void paint(Graphics g) {} } Application Application has a single start point which is main method public class MyClass { public static void main(String args[]) {} }

CSI 3125, Preliminaries, page 6 Applet An applet program is written as a inheritance of the java.applet.Applet class Applet must be subclass of java.applet.Applet ie import java.applet.Applet; Or import java.applet.*; And extends the Applet class ( for creating sub class of Applet class) And Override the Applet class Methods ( init(), start(), stop(), & destroy() )

CSI 3125, Preliminaries, page 7 Applet Life Cycle Applet 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. public void paint(): it is inherited from java.awt It invoke immediately after start() method Used to paint the Applet. It provides Graphics class object that can be used for drawing oval, rectangle, arc etc.

CSI 3125, Preliminaries, page 8 Applet Life Cycle

CSI 3125, Preliminaries, page 9 Applet Life Cycle Browser visits page containing an applet – Browser calls init on that applet, once – Browser calls start on that applet Browser goes away from that page – Browser calls stop on that applet Browser comes back to that page – Browser calls start again on that applet Browser shuts down – Browser calls destroy on the applet, once

CSI 3125, Preliminaries, page 10 Run an Applet There are two ways to run an applet 1) By html file. 2) By appletViewer tool (for testing purpose). To execute the applet by html file, create an applet and compile it. Create an html file which embedded the.class file of java with applet code tag in html file.

CSI 3125, Preliminaries, page 11 tag 1) By html file. <APPLET  // the beginning of the HTML applet code CODE=“my.class“  // the actual name of the applet (usually a 'class' file) WIDTH="100“  // the physical width of the applet on the page HEIGHT="50“  // the physical height of the applet on the page ALIGN="Top“  // align the applet within its page space (top, bottom, center)

CSI 3125, Preliminaries, page 12 Applet example 1) By html file //First.java import java.applet.Applet; import java.awt.Graphics; public class First extends Applet{ public void paint(Graphics g){ g.drawString("welcome",150,150); } } after compiling (javac First.java) //run.html

CSI 3125, Preliminaries, page 13 Applet By 2) appletViewer tool To execute the applet by appletviewer tool, create an applet that contains applet tag in comment and compile it. First.java javac first.java After that run it by: appletviewer First.java. Now Html file is not required but it is for testing purpose only.

CSI 3125, Preliminaries, page 14 Applet By 2) appletViewer tool To execute the applet by appletviewer tool, create an applet that contains applet tag in comment and compile it. First.java javac first.java After that run it by: appletviewer First.java. Now Html file is not required but it is for testing purpose only.

CSI 3125, Preliminaries, page 15 Applet example 2) appletViewer tool //First.java /* */ import java.applet.Applet; import java.awt.Graphics; public class First extends Applet{ public void paint(Graphics g){ g.drawString("welcome",150,150); } } after compiling c:\>javac First.java c:\>appletviewer First.java