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CIS3023: Programming Fundamentals for CIS Majors II Summer 2010

CIS3023: Programming Fundamentals for CIS Majors II Summer 2010. Introduction to Applets. Course Lecture Slides 29 th July 2010. Ganesh Viswanathan. Applets.

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CIS3023: Programming Fundamentals for CIS Majors II Summer 2010

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  1. CIS3023: Programming Fundamentals for CIS Majors II Summer 2010 Introduction to Applets Course Lecture Slides29thJuly 2010 GaneshViswanathan

  2. Applets • Applets are small applications accessed on an Internet server, transported over the networks, automatically installed and run as part of a web document. • At the client, applets get limited access to resources to be able to produce graphics, multimedia UI, run computations, etc. without risk of viruses or breaching data integrity.

  3. Applets • Applet Code Example: HelloWorld.java import java.awt.Graphics; import java.applet.Applet; public class HelloWorldextendsApplet{ public void paint(Graphics g){ g.drawString("Hello World!", 120, 80); } } Every applet must be a subclass of Applet.

  4. Applets • Web document: HelloWorld.html <HTML> <HEAD><TITLE>Applet example</TITLE> </HEAD> <BODY> <APPLET code="HelloWorld.class" width="300px" height="200px"></APPLET> </BODY> </HTML>

  5. Abstract Window Toolkit (AWT) • The Abstract Window Toolkit (AWT) is Java's original platform-independent windowing, graphics, and user-interface widget toolkit. • Applets interact with the user through the AWT, not through the console-based I/O classes. • AWT is a part of Java Foundation Classes (JFC),the standard API for providing a graphical user interface (GUI) for a Java program.

  6. Abstract Window Toolkit (AWT) • AWT contains support for a window-based, graphical interface. • AWT supports graphics through components (visible UI elements-buttons/ labels/ textfields) and containers (components that contain and organize other components). • All containers inherit from the java.awt.Container base class, which itself inherits from java.awt.Component

  7. Applets • Do not have main() method • Instead applet begins execution when the name of its class is passed to an applet viewer or to a network browser. • Compile the applet in the same way as a normal java application) • In the example, the paint() method defined by AWT and overridden by the applet helps to redraw output on screen.

  8. Applets • Applets are event-driven. • User initiates interaction with an applet. These interactions are sent to the applet as “events” to which the applet must respond. • Example: When the user clicks on a button in the applet window, a button-click event is generated.

  9. Applets • In your applet override a set of methods that help the browser or applet-viewer to interface to the applet and control its execution. • Applet class defines – init(), start(), stop(), destroy() • AWT Component class defines paint() method.

  10. Applet Skeleton • import java.awt.*; • import java.applet.*; • public class MyAppletSkeleton extends Applet { • // browser calls init when applet is first loaded • public void init( ){ /* initialization */ } • // called second, after init. Also called whenever applet is restarted • public void start( ){ /* start or resume execution */ } • //called when the applet is stopped • public void stop( ){ /* suspends execution */ } • //called when applet is terminated. Last method executed • public void destroy( ){ /* perform shutdown operations */ } • //called when an applet’s window must be restored (redrawn) • public void paint(Graphics g){ /* redisplay contents of window */ } • }

  11. Applet Skeleton • import java.awt.*; • import java.applet.*; • public class MyAppletSkeleton extends Applet { • // browser calls init when applet is first loaded • public void init( ){ /* initialization */ } • // called second, after init. Also called whenever applet is restarted. • public void start( ){ /* start or resume execution */ } • //called when the applet is stopped. • public void stop( ){ /* suspends execution */ } • //called when applet is terminated. Last method executed. • public void destroy( ){ /* perform shutdown operations */ } • //called when an applet’s window must be restored (redrawn) • public void paint(Graphics g){ /* redisplay contents of window */ } • }

  12. Applets • Further examples.

  13. Get more info! • Java docs: java.applet • http://download-llnw.oracle.com/javase/1.5.0/docs/api/java/applet/package-summary.html • Java docs: java.awt http://java.sun.com/j2se/1.5.0/docs/api/java/awt/package-summary.html • http://java.sun.com/products/jdk/awt/#what • JFC • http://docstore.mik.ua/orelly/java-ent/jfc/ch02_04.htm#jfcnut-ch-2-tab-awtcont

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